Location
At the junction of the Yangtze and the Tuo rivers, Luzhou is located in southeastern Sichuan Province and borders Chongqing Municipality, Guizhou and Yunnan Provinces.
History
The history of Luzhou dates back to Xia (1600 BC) and Shang (1100 BC) Dynasties. Luzhou became a prefecture level city in 1983.
History of Luzhou
Luzhou, a well-known historic and cultural city in China, boasting a long history of more than 2000 years. Dating back to 7,000 years ago, this area of present-day Luzhou was inhabited by human beings. Early in the Shang and Zhou period, 11th century BC, Luzhou was an appendage in the State of Ba. Later in 316 BC, Ba prefecture which included most part of Luzhou was established by Emperor Huiwen of the Qin Dynasty (221 BC-208 BC) after his conquering of the State of Ba and Shu. During this period, great improvement in economy and culture was achieved in aspect of the advanced production technique and culture introduced by the immigrants from the middle land. In Western Han Dynasty (206 BC-AD 23) , Jiangyang county was set up in the area of current Jiangyang district where the Tuojing river and Yangtze river emerged. Then, in order to exploit the southwest region, Emperor Wu of Eastern Han Dynasty (25-220) expanded this county. As a result, Luzhou became a prime bordering county which was the portal of Tuojing river and the barrier of western Sichuan, which brought great prosperity to salt-refinery and agriculture. Song Dynasty (196-1127) was a splendid time throughout Luzhou’s history since it bloomed into a rich and populous place with fertile and profound land, flourishing agriculture and blooming business. It was known as the natural granary of southern Shu. Furthermore, wine-making industry and salt-refinery were in larger expansion. The method to decoct salt with natural gas was discovered at that time according to ancient literature. In addition, trade and business between the residents and ethnic groups was popular and protective wall as well as forts were constructed by the local government. In Yuan Dynasty (1279-1368), Luzhou remained an important place of wine-making, salt-refinery and tea-making industries. A large number of wooden ships were made to activate shipping industry, promoting the exchange of goods with the outside. In 1373, Ming Dynasty (1644-1911), waves of immigrants from other parts of China brought rapid growth in economy and culture. Luzhou served as a political, economic, martial and cultural center where Sichuan, Guizhou and Yunnan met. December 6, 1949 saw the liberation of Luzhou. Later in 1960, it became a city under the government of Sichuan province, encompassing 5 counties which originally belonged to Yibin city. Given an comprehensive reform under the guidance of reform and opening policy, Luzhou gradually stepped into market economy. Nowadays, it is regarded as the nationally key base of chemical lines, machinery and wine-making industry.
Historic and Cultural Relics
Bao’en Pagoda
Located directly in the downtown of Luzhou, Bao’en pagoda was built in 1148, southern Song Dynasty, and was maintained respectively in 1983 and 1985, []Qing Dynasty]]. Being 33.3 m high, it is an octagon brick and stone structure of seven-layer pavilion style. It has a bronze top and there are 107 steps in its spiral flight. The base is an octagon of 4.1 m each side, 4.5 m high; inside it are 256 figures set in 90 niches. The Bao’en pagoda was listed by the People’s Government of Sichuan Province as a historical and culture relic under provincial protection in April 1991.
Dragon Head Bridge
Constructed in Ming Dynasty, Dragon Head Bridge spans over the Nine Bends Creek and is a precious stone bridge with distinctive style of Ming Dynasty around the country. 5m high, 54 m long and 1.9 m wide, the bridge has 14 piers separating it into 13 organs. The eight piers amongst the mid section was characterized by carved traditionally auspicious beast, such as huge dragon, lion, elephant and kylin. It was announced as a key national culture relic in 1996.
Longtou Pass
Longtou Pass, about 2.5 km long, is located in the southern suburban area of Luzhou, with construction that started in Han Dynasty when Emperor Guangxu was in his reign. Bordering Tuojiang river in the north and Yangtze river in the south, it obtains the name, Longtou Pass, since it looks like a huge dragon passing through these two rivers .It is the only land-path because Luzhou is a city surrounded by rivers in other three sides. Longtou Pass is the very place where Liu Bocheng waged Luzhou Uprising and it was listed as a protected historic and cultural relic of Luzhou in April 1984 and a provincial one in 1996.
National Vintage Square
National Vintage Square located in the bustling commercial center of Luzhou is a typical engineering image representing the strong aroma of Luzhou Vintage. It is a scientifically planned and beautified square with a serene environment and clear arrangement, set off by surroundings – truly a place makes you feel mellow when you are roaming. Here remain 460 cellars of the Ming and Qing dynasties when wine was made by hand, which has created considerable economic efficiency for four centuries and become a wonder in the world’s wine brewing history for its exceptional value in economy, history and culture.
Being situated in Xuyong county, Spring and Autumn Temple was built in 1906, Qing Dynasty. Originally, it was a temple for Guany (the Lord of Guan) and then rebuilt as an assembly hall of some merchants doing salt business from Shaanxi. It is well-known for its distinctive architecture style, including fine sculpt, vivid shape, artistic conception and has been listed as a protected historic and cultural relic of Luzhou.
Baizitu
Baizitu lies by the Tuojiang river, the northwestern corner of Luzhou city. Its got the name Baizitu for the stone inscription of the Qing Dynasty and was the protected historic and cultural relic of Luzhou.
Economy
Luzhou has always been a hub of economic activities in the tri-province border area of Sichuan, Yunnan, and Guizhou. Food, liquor, and chemicals production, along with construction equipment manufacturing are the most important industries of the local economy. Total GDP reached 33.11 billion yuan in 2006 (per capita 7,819 yuan).
Liquor industry
Luzhou Old Cellar and Langjiu are the two best known brands of liquor with national and international reputation.
Wine Industry in Luzhou Boasting a long history of wine industry, Luzhou is renowned at home and abroad for its well-known liquors like Luzhou Vintage and Gulin Lang Wine. It is a nationally famous wine industry base and wine city. Luzhou has developed into nationally comprehensive system of wine industry, concentrating on Luzhou Vintage Co. Ltd and Lang Wine Factory. Over 200 wine products are listed as national and provincial wine with high grade and have good market in China and other countries and districts around the world. Luzhou Vintage and Lang Wine are two of the six nationally famous wines in Sichuan province, which makes it become one of the three districts enjoying two nationally famous wines in China.
Luzhou Laojiao 1573
Machine Building Industry
Luzhou is one of the nine largest machine building industry production bases in China and the manufacturing center of entirely hydraulic truck crane and excavator. Changjiang Engineering Machine Group consists of Changjiang Crane Factory, Changjiang Hydraulic Device Factory, Changiang Excavator Factory (now Sichuan Bonny Heavy Machinery Co.). A extended production system producing national engineering machine mainframe and basic devices and offering maintenance has came into being. Among the cities along Yangtze River, Luzhou enjoys the second largest production of entirely hydraulic truck machine, just being next to Shanghai. Changjiang Crane Factory being directly under this huge group is a large scale enterprise which has the longest history of producing entirely hydraulic automobile crane, most complete devices and strong carrying capacity and is entitled as the” National Manufacturing Center of Entirely Hydraulic Machine”. It is also the birthplace of the first entirely hydraulic automobile crane in our county. Twelve hydraulic cranes researched and produced with advanced standards in 1980s stand the world, whose carrying capacity ranked No.5 around the world, No.2 in Asia, No.1 in China. Changjiang Excavator Factory is an important and large scale enterprise of Ministry of Construction and the only one excavator factory with full series of service. Its new product, WY160 crane, had obtained the ‘Golden Dragon Award “and “Silver Quality Award” granted by the state and R982 hydraulic crane has the largest dipper capacity in China. Changjiang Hydraulic Devices Factory is the key enterprise appointed by Ministry of Machine-Building Industry and Electronics Industry to produce hydraulic components and devices. Its products has expanding market around the world and enjoys good reputation among the domestic counterparts and customers.
Chemical Industry
Chemical industry is the largest and most promising pillar industry of Luzhou, especially the natural gas industry. Luzhou is one of the 16 largest chemical industry bases and 16 fine chemical industry bases decided by the National Ministry of Chemical Industry. At present, the chemical industry of Luzhou has developed into a national chemical industry system covering production, education, scientific research, design, machine and architecture. A group of nationally large scale enterprises with well equipment and strong finance and technique power have been established and achieved the globally advanced level. Lutianhua enterprise is the most extended carbamide and oil chemical production bases, owning the largest device to produce fatty acid, fatty amine, synthetic ammonia and carbamide. Its annual output of carbamide is 1.24 million tons and synthetic ammonia 0.9 million tons. It is one of the 500 national largest enterprises. Tianhua Co, Ltd is a key enterprise which brings in synthetic ammonia 0.3 million tons and carbamide 0.6 million tons, processing two sets of chemical fertilizer devices with world technical levels. Luzhou Chemical Factory is a united enterprise undertaking military and civil chemical production. State-owned Torch Chemical Factory is the only production base of "801" and gained the national quality golden award , surpassing the America Standard.
Tourism Industry
Luzhou is one of the China Excellent Tourist Cities with many scenic spots and historic sites, such as Yuchan scenic spot in Luxian county, Fobao scenic spot in Hejiang county, Mt. Fangshan scenic spot in Jiangyang county, the litchi and longan orchard along the Yangtze River and Tuojiang River, Nine Lions scenic spot, the Mt. Phoenix in Naxi county, Huangjin virginal forest in Gulin county, etc. With the official approbation of National Ministry of Forestry, Fobao Forest Park became the National Forestry Park and was elected as “AAA” tourist attraction in 2001 by National Tourism Administration and the ‘AA” was granted to Yuchan and Mt. Fangshan scenic sports. Besides, Luzhou city and Xuyong county is respectively the nationally and provincially historic and cultural city. Wine Cellar of Luzhou Vintage constructed in Ming Dynasty and Dragon Head Bridge were listed as a key protected cultural relic of the state. There are more than ten protected historical relics of Sichuan Province, including the site of Red Army’s Four-time Crossing the Chishui River, Yuchan scenic spot, Spring and Autumn Temple, etc. The Taiping Ferry Museum for the Red Army’s Four-time Crossing the Chishui River is nominated the “National Demonstration base for patriotic education” by the central Propaganda Ministry in 2001. Moreover, the Sci-tech Park of Luzhou Vintage is the national industry tourism demonstration spot and Luzhou Zhangba Longan Orchard is the national agricultural tourism spot. Some other famous tourist attractions are available in Luzhou’s neighboring cities including Leshan, Yibin, Zigong and Chongqing. There are there national scenic spots nearby comprising Bamboo Forest scenic spot, Mt. Simianshan in Chongqing and Sidong Channel in Guizhou Province.
Agriculture
Luzhou is a key comprehensive development zone in the upper Yangtze River and Sichuan province as well as an important production base of commodity grain, fruit, cured tobacco and poultry, including fine rice, litchi, longan, tea, traditional Chinese medicine material, pod, etc.
Transportation
Luzhou has the largest river port in Sichuan on the upper Yangtze, with the capability to load and unload containerships. Expressways connecting to Chengdu and Chongqing were completed in the 1990s. Railroads and an airport provide additional links to several cities in China.
An expressway connecting Luzhou and Longchang is in use and another which is going to connect the city directly with Chongqing is under construction.
Luzhou International Container Pier
The Luzhou International Container Pier handled 4,505 containers in May 2007.
Luzhou Airport
Luzhou Airport was built in 1945 and initially served an air route between China and India by the US Air Force during the World War II. Services were suspended in the 1960s, but later it was used for training purposes by the Chinese Air Force. Major renovations and expansions were completed in January 2001, and now the airport serves direct flights to Beijing, Guangzhou, Kunming, Guiyang and Shenzhen.
Flight information:
Geographical Condition and Climate
Geographical Conditions
Luzhou is situated in the northeast of Sichuan province, a meeting place of Sichuan, Guizhou and Chongqing, with a longitude 105o 08’ 41” E~ 106o 28’E and latitude 27o 39’ N~29o 20’N. Covering a total area of 12246.87 sq km, it is 121.64 km long from east to west and 181.84 km wide from south to north. As a prefecture-level city of Sichuan with a registered population of 4.8 million, Luzhou is 267 km away from Chengdu, the capital of Sichuan province, and adjacent to Chongqing in the east, bordering Guizhou and Yunnan provinces in the south, Yibin city and Zizhong city in the west, Chongqing and Neijiang in the north. The city governs 7 administrative divisions, including 3 districts (Jiangyang, Longma, Naxi ) and 4 counties ( Luxian, Hejiang, Xuyong, Gulin ).
Owning to its position in the southern peripheral area of Sichuan Basin and the connective region with Yunnan and Guizhou plateau, the hypsography of Luzhou is characterized by the river valise, hills, and level lands in the north and highland, mountains, sheer valise and rushing rivers in the south, which bring thriving fishing and agriculture to the northern area and rich forest and mineral resources to the southern region respectively. The lowest part is 203 meters, which lies on the surface of Yangtze river in Jiucengyan, Hejiang county while the highest one located at the peak of Liangzi mountain, Xuyong county, reaching 1902 meters. Moreover, Luzhou is also a city covered by rivers. The Yangtze river is running through the whole area from west to east covering a course of 133 km totally and the maximum flood level is 18.68 meters during the past 30 years. Besides, there are many other rivers converging here, such as Tuo river, Yongling river, Chishui river, Laixi river etc.
Climate
Luzhou generally enjoys subtropical humid climate with vertical climate in the southern mountain area, featuring distinctive seasons, relatively high temperature, rich sunshine, ample rainfall, long frost-free period and that the elements of light, water and heat almost occur in the same season, which offers a suitable environment to the development of agriculture. It’s annual average temperature is around 17.1oC~18.5oC, July being the hottest month ( average temp. 27.5oC ) and January the coldest ( average temp. 7oC ) and the daily difference in temperature is about 6oC.Snow is rare here. The annual average precipitation is 748.4 mm~1184.2 mm and there is not much rainfall in winter and spring while is affluence in summer and autumn. The precipitation from May to September accounts for 79.2 of the year’s total. As the total sunshine hours averages 1200~1400 and the frost-free period lasts 300~358 days, the corp. growth period is relatively long.
2009年1月18日星期日
Polyethylene
Description
Polyethylene is a polymer consisting of long chains of the monomer ethylene (IUPAC name ethene). The recommended scientific name polyethene is systematically derived from the scientific name of the monomer . In certain circumstances it is useful to use a structure–based nomenclature; in such cases IUPAC recommends poly(methylene) (poly(methanediyl) is an non-preferred alternative ). The difference in names between the two systems is due to the opening up of the monomer's double bond upon polymerisation.
In the polymer industry the name is sometimes shortened to PE in a manner similar to that by which other polymers like polypropylene and polystyrene are shortened to PP and PS respectively. In the United Kingdom the polymer is commonly called polythene, although this is not recognized scientifically.
The ethene molecule (known almost universally by its common name ethylene) C2H4 is CH2=CH2, Two CH2 groups connected by a double bond, thus:
Polyethylene contains the chemical elements carbon and hydrogen.
Polyethylene is created through polymerization of ethene. It can be produced through radical polymerization, anionic addition polymerization, ion coordination polymerization or cationic addition polymerization. This is because ethene does not have any substituent groups that influence the stability of the propagation head of the polymer. Each of these methods results in a different type of polyethylene.
Classification
Polyethylene is classified into several different categories based mostly on its density and branching. The mechanical properties of PE depend significantly on variables such as the extent and type of branching, the crystal structure and the molecular weight.
Ultra high molecular weight polyethylene (UHMWPE)
Ultra low molecular weight polyethylene (ULMWPE or PE-WAX)
High molecular weight polyethylene (HMWPE)
High density polyethylene (HDPE)
High density cross-linked polyethylene (HDXLPE)
Cross-linked polyethylene (PEX or XLPE)
Medium density polyethylene (MDPE)
Low density polyethylene (LDPE)
Linear low density polyethylene (LLDPE)
Very low density polyethylene (VLDPE)
UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.1 and 5.67 million. The high molecular weight results in less efficient packing of the chains into the crystal structure as evidenced by densities of less than high density polyethylene (for example, 0.930–0.935 g/cm3). The high molecular weight results in a very tough material. UHMWPE can be made through any catalyst technology, although Ziegler catalysts are most common. Because of its outstanding toughness and its cut, wear and excellent chemical resistance, UHMWPE is used in a wide diversity of applications. These include can and bottle handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks and butchers' chopping boards. It competes with Aramid in bulletproof vests, under the tradenames Spectra and Dyneema, and is commonly used for the construction of articular portions of implants used for hip and knee replacements.
HDPE is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium catalysts or Ziegler-Natta catalysts) and reaction conditions. HDPE is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes.
PEX is a medium- to high-density polyethylene containing cross-link bonds introduced into the polymer structure, changing the thermoplast into an elastomer. The high-temperature properties of the polymer are improved, its flow is reduced and its chemical resistance is enhanced. PEX is used in some potable-water plumbing systems because tubes made of the material can be expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water-tight, connection.
MDPE is defined by a density range of 0.926–0.940 g/cm3. MDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. MDPE has good shock and drop resistance properties. It also is less notch sensitive than HDPE, stress cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw closures.
LLDPE is defined by a density range of 0.915–0.925 g/cm3. LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). LLDPE has higher tensile strength than LDPE, it exhibits higher impact and puncture resistance than LDPE. Lower thickness (gauge) films can be blown, compared with LDPE, with better environmental stress cracking resistance but is not as easy to process. LLDPE is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to LDPE. Cable covering, toys, lids, buckets, containers and pipe. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility and relative transparency.
LDPE is defined by a density range of 0.910–0.940 g/cm3. LDPE has a high degree of short and long chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. LDPE is created by free radical polymerization. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap.
VLDPE is defined by a density range of 0.880–0.915 g/cm3. VLDPE is a substantially linear polymer with high levels of short-chain branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). VLDPE is most commonly produced using metallocene catalysts due to the greater co-monomer incorporation exhibited by these catalysts. VLDPEs are used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap as well as impact modifiers when blended with other polymers.
Recently much research activity has focused on the nature and distribution of long chain branches in polyethylene. In HDPE a relatively small number of these branches, perhaps 1 in 100 or 1,000 branches per backbone carbon, can significantly affect the rheological properties of the polymer.
Ethylene copolymers
In addition to copolymerization with alpha-olefins, ethylene can also be copolymerized with a wide range of other monomers and ionic composition that creates ionized free radicals. Common examples include vinyl acetate (the resulting product is ethylene-vinyl acetate copolymer, or EVA, widely used in athletic-shoe sole foams) and a variety of acrylates (applications include packaging and sporting goods).
History
Polyethylene was first synthesized by the German chemist Hans von Pechmann who prepared it by accident in 1898 while heating diazomethane. When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy, substance that he had created they recognized that it contained long -CH2- chains and termed it polymethylene.
The first industrially practical polyethylene synthesis was discovered (again by accident) in 1933 by Eric Fawcett and Reginald Gibson at the ICI works in Northwich, England. Upon applying extremely high pressure (several hundred atmospheres) to a mixture of ethylene and benzaldehyde they again produced a white, waxy, material. Because the reaction had been initiated by trace oxygen contamination in their apparatus the experiment was, at first, difficult to reproduce. It was not until 1935 that another ICI chemist, Michael Perrin, developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial LDPE production beginning in 1939.
Subsequent landmarks in polyethylene synthesis have revolved around the development of several types of catalyst that promote ethylene polymerization at more mild temperatures and pressures. The first of these was a chromium trioxide-based catalyst discovered in 1951 by Robert Banks and J. Paul Hogan at Phillips Petroleum. In 1953 the German chemist Karl Ziegler developed a catalytic system based on titanium halides and organoaluminium compounds that worked at even milder conditions than the Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are used in industrial practice.
By the end of the 1950s both the Phillips- and Ziegler-type catalysts were being used for HDPE production. Phillips initially had difficulties producing a HDPE product of uniform quality and filled warehouses with off-specification plastic. However, financial ruin was unexpectedly averted in 1957 when the hula hoop, a toy consisting of a circular polyethylene tube, became a fad among youth in the United States.
A third type of catalytic system, one based on metallocenes, was discovered in 1976 in Germany by Walter Kaminsky and Hansjörg Sinn. The Ziegler and metallocene catalyst families have since proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very low-density polyethylene and linear low-density polyethylene. Such resins, in the form of fibers like Dyneema, have (as of 2005) begun to replace aramids in many high-strength applications.
Until recently the metallocenes were the most active single-site catalysts for ethylene polymerisation known—new catalysts are typically compared to zirconocene dichloride. Much effort is currently being exerted on developing new, single-site (so-called post-metallocene) catalysts that may allow greater tuning of the polymer structure than is possible with metallocenes. Recently work by Fujita at the Mitsui corporation (amongst others) has demonstrated that certain salicylaldimine complexes of Group 4 metals show substantially higher activity than the metallocenes.
Physical properties
Depending on the crystallinity and molecular weight, a melting point and glass transition may or may not be observable. The temperature at which these occur varies strongly with the type of polyethylene. For common commercial grades of medium- and high-density polyethylene the melting point is typically in the range 120 to 130 °C ((250 to 265 °F). The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (220 to 240 °F).
Most LDPE, MDPE and HDPE grades have excellent chemical resistance and do not dissolve at room temperature because of their crystallinity. Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in aromatic hydrocarbons such as toluene or xylene, or in chlorinated solvents such as trichloroethane or trichlorobenzene.
Environmental issues
The wide use of polyethylene makes it an important environmental issue. Though it can be recycled, most of the commercial polyethylene ends up in landfills and in the oceans (notably the Great Pacific Garbage Patch). Polyethylene is not considered biodegradable, as it takes several centuries until it is efficiently degraded. Recently (May 2008) Daniel Burd, a 16 year old Canadian, won the Canada-Wide Science Fair in Ottawa after discovering that Sphingomonas, a type of bacteria, can degrade over 40% of the weight of plastic bags in less than three months. The applicability of this finding is still a matter for the future.
Biopolyethylene
Main article: Bioplastics
Braskem and Toyota Tsusho Corporation started Joint marketing activities for producing green polyethylene from sugar cane. Braskem will build a new facility at their existing industrial unit in Triunfo, RS, Brazil with an annual production capacity of 200,000 tons, and will produce High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE) from bioethanol derived from sugarcane .
Polyethylene is a polymer consisting of long chains of the monomer ethylene (IUPAC name ethene). The recommended scientific name polyethene is systematically derived from the scientific name of the monomer . In certain circumstances it is useful to use a structure–based nomenclature; in such cases IUPAC recommends poly(methylene) (poly(methanediyl) is an non-preferred alternative ). The difference in names between the two systems is due to the opening up of the monomer's double bond upon polymerisation.
In the polymer industry the name is sometimes shortened to PE in a manner similar to that by which other polymers like polypropylene and polystyrene are shortened to PP and PS respectively. In the United Kingdom the polymer is commonly called polythene, although this is not recognized scientifically.
The ethene molecule (known almost universally by its common name ethylene) C2H4 is CH2=CH2, Two CH2 groups connected by a double bond, thus:
Polyethylene contains the chemical elements carbon and hydrogen.
Polyethylene is created through polymerization of ethene. It can be produced through radical polymerization, anionic addition polymerization, ion coordination polymerization or cationic addition polymerization. This is because ethene does not have any substituent groups that influence the stability of the propagation head of the polymer. Each of these methods results in a different type of polyethylene.
Classification
Polyethylene is classified into several different categories based mostly on its density and branching. The mechanical properties of PE depend significantly on variables such as the extent and type of branching, the crystal structure and the molecular weight.
Ultra high molecular weight polyethylene (UHMWPE)
Ultra low molecular weight polyethylene (ULMWPE or PE-WAX)
High molecular weight polyethylene (HMWPE)
High density polyethylene (HDPE)
High density cross-linked polyethylene (HDXLPE)
Cross-linked polyethylene (PEX or XLPE)
Medium density polyethylene (MDPE)
Low density polyethylene (LDPE)
Linear low density polyethylene (LLDPE)
Very low density polyethylene (VLDPE)
UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.1 and 5.67 million. The high molecular weight results in less efficient packing of the chains into the crystal structure as evidenced by densities of less than high density polyethylene (for example, 0.930–0.935 g/cm3). The high molecular weight results in a very tough material. UHMWPE can be made through any catalyst technology, although Ziegler catalysts are most common. Because of its outstanding toughness and its cut, wear and excellent chemical resistance, UHMWPE is used in a wide diversity of applications. These include can and bottle handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks and butchers' chopping boards. It competes with Aramid in bulletproof vests, under the tradenames Spectra and Dyneema, and is commonly used for the construction of articular portions of implants used for hip and knee replacements.
HDPE is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium catalysts or Ziegler-Natta catalysts) and reaction conditions. HDPE is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes.
PEX is a medium- to high-density polyethylene containing cross-link bonds introduced into the polymer structure, changing the thermoplast into an elastomer. The high-temperature properties of the polymer are improved, its flow is reduced and its chemical resistance is enhanced. PEX is used in some potable-water plumbing systems because tubes made of the material can be expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water-tight, connection.
MDPE is defined by a density range of 0.926–0.940 g/cm3. MDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. MDPE has good shock and drop resistance properties. It also is less notch sensitive than HDPE, stress cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw closures.
LLDPE is defined by a density range of 0.915–0.925 g/cm3. LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). LLDPE has higher tensile strength than LDPE, it exhibits higher impact and puncture resistance than LDPE. Lower thickness (gauge) films can be blown, compared with LDPE, with better environmental stress cracking resistance but is not as easy to process. LLDPE is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to LDPE. Cable covering, toys, lids, buckets, containers and pipe. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility and relative transparency.
LDPE is defined by a density range of 0.910–0.940 g/cm3. LDPE has a high degree of short and long chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. LDPE is created by free radical polymerization. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap.
VLDPE is defined by a density range of 0.880–0.915 g/cm3. VLDPE is a substantially linear polymer with high levels of short-chain branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). VLDPE is most commonly produced using metallocene catalysts due to the greater co-monomer incorporation exhibited by these catalysts. VLDPEs are used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap as well as impact modifiers when blended with other polymers.
Recently much research activity has focused on the nature and distribution of long chain branches in polyethylene. In HDPE a relatively small number of these branches, perhaps 1 in 100 or 1,000 branches per backbone carbon, can significantly affect the rheological properties of the polymer.
Ethylene copolymers
In addition to copolymerization with alpha-olefins, ethylene can also be copolymerized with a wide range of other monomers and ionic composition that creates ionized free radicals. Common examples include vinyl acetate (the resulting product is ethylene-vinyl acetate copolymer, or EVA, widely used in athletic-shoe sole foams) and a variety of acrylates (applications include packaging and sporting goods).
History
Polyethylene was first synthesized by the German chemist Hans von Pechmann who prepared it by accident in 1898 while heating diazomethane. When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy, substance that he had created they recognized that it contained long -CH2- chains and termed it polymethylene.
The first industrially practical polyethylene synthesis was discovered (again by accident) in 1933 by Eric Fawcett and Reginald Gibson at the ICI works in Northwich, England. Upon applying extremely high pressure (several hundred atmospheres) to a mixture of ethylene and benzaldehyde they again produced a white, waxy, material. Because the reaction had been initiated by trace oxygen contamination in their apparatus the experiment was, at first, difficult to reproduce. It was not until 1935 that another ICI chemist, Michael Perrin, developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial LDPE production beginning in 1939.
Subsequent landmarks in polyethylene synthesis have revolved around the development of several types of catalyst that promote ethylene polymerization at more mild temperatures and pressures. The first of these was a chromium trioxide-based catalyst discovered in 1951 by Robert Banks and J. Paul Hogan at Phillips Petroleum. In 1953 the German chemist Karl Ziegler developed a catalytic system based on titanium halides and organoaluminium compounds that worked at even milder conditions than the Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are used in industrial practice.
By the end of the 1950s both the Phillips- and Ziegler-type catalysts were being used for HDPE production. Phillips initially had difficulties producing a HDPE product of uniform quality and filled warehouses with off-specification plastic. However, financial ruin was unexpectedly averted in 1957 when the hula hoop, a toy consisting of a circular polyethylene tube, became a fad among youth in the United States.
A third type of catalytic system, one based on metallocenes, was discovered in 1976 in Germany by Walter Kaminsky and Hansjörg Sinn. The Ziegler and metallocene catalyst families have since proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very low-density polyethylene and linear low-density polyethylene. Such resins, in the form of fibers like Dyneema, have (as of 2005) begun to replace aramids in many high-strength applications.
Until recently the metallocenes were the most active single-site catalysts for ethylene polymerisation known—new catalysts are typically compared to zirconocene dichloride. Much effort is currently being exerted on developing new, single-site (so-called post-metallocene) catalysts that may allow greater tuning of the polymer structure than is possible with metallocenes. Recently work by Fujita at the Mitsui corporation (amongst others) has demonstrated that certain salicylaldimine complexes of Group 4 metals show substantially higher activity than the metallocenes.
Physical properties
Depending on the crystallinity and molecular weight, a melting point and glass transition may or may not be observable. The temperature at which these occur varies strongly with the type of polyethylene. For common commercial grades of medium- and high-density polyethylene the melting point is typically in the range 120 to 130 °C ((250 to 265 °F). The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (220 to 240 °F).
Most LDPE, MDPE and HDPE grades have excellent chemical resistance and do not dissolve at room temperature because of their crystallinity. Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in aromatic hydrocarbons such as toluene or xylene, or in chlorinated solvents such as trichloroethane or trichlorobenzene.
Environmental issues
The wide use of polyethylene makes it an important environmental issue. Though it can be recycled, most of the commercial polyethylene ends up in landfills and in the oceans (notably the Great Pacific Garbage Patch). Polyethylene is not considered biodegradable, as it takes several centuries until it is efficiently degraded. Recently (May 2008) Daniel Burd, a 16 year old Canadian, won the Canada-Wide Science Fair in Ottawa after discovering that Sphingomonas, a type of bacteria, can degrade over 40% of the weight of plastic bags in less than three months. The applicability of this finding is still a matter for the future.
Biopolyethylene
Main article: Bioplastics
Braskem and Toyota Tsusho Corporation started Joint marketing activities for producing green polyethylene from sugar cane. Braskem will build a new facility at their existing industrial unit in Triunfo, RS, Brazil with an annual production capacity of 200,000 tons, and will produce High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE) from bioethanol derived from sugarcane .
Vera Bradley
History
The company was founded in March 1982 by Patricia Miller and Barbara Bradley Baekgaard, a 1962 graduate of Marymount College. Named after Baekgaard's mother, the company got its start when both were inspired while awaiting a flight in Atlanta, where they noticed a "definite lack of feminine-looking luggage".
Products
A Peacock-patterned Vera Bradley bag.
Vera Bradley bags come in many sizes and styles, as well as many different patterns and colors. There are travel duffels, medium sized totes, large totes, purses, wallets, eyeglass and sunglass cases, cosmetic cases, and jewelry cases. There are also umbrellas, napkins, placemats, rolling luggage, tableware, bedding, fine rugs, accessory coverings, and stationery. Pet collars, beds, leashes, and carriers for small dogs, cats, and rabbits were also available for a limited time. The purses come with a variety of names such as the Vera, the Bucket Tote, and the Audrey. After a pattern is on the market for a while, the company retires it. When patterns retire, new ones are produced. New patterns are released in spring and fall colors; they are typically introduced in January and July. The company will also retire or redesign specific styles and new styles may be introduced in concurrence with the new patterns.
Within the past few years, Vera Bradley has become increasingly popular with many women for a variety of reasons. Compared to other, more expensive handbag lines, Vera Bradley offers an affordable yet stylish solution to the search for an everyday handbag. The bags are handy and useful, many with multiple pockets inside and outside the bag. Furthermore, all handbags/totes/travel bags are washable, as long as the cardboard base is removed. Accessories and Microfiber lines can be spot cleaned. Overall, the product is successful due to its lightweight, comfortable, and attractive feel. With over 15 patterns available at any given time, there is a pattern and bag style to appeal to every woman.
Collections
All collections are available in a variety of colors and patterns.
Patterns
The following patterns are active patterns, currently available in all Vera Bradley Signature Stores and Retailers:
Hope Garden, Purple Punch, Cupcakes Green, and Cupcakes Pink, released Jan. 09.
Mediterranean Blue, Mediterranean White, and Mosaic, released Sept. 08.
Frankly Scarlet, Caffe Latte, Puccini, and Night Owl, released June 08.
Raspberry Fizz, Daisy Daisy, Yellow Bird, and Pinwheel Pink, released Jan. 08.
Mod Floral Pink and Mod Floral Blue, released July 07.
Java Blue, released Jan. 06. *Java Blue is the longest running pattern in Vera Bradley history*
Vera Bradley makes dozens of different types of handbags ranging from wristlets to large totes. Some names include the Amy, the Hipster, the Tote, the Morgan, the Hannah, the Betsy and the Villager. The handbags are made out of washable quilted cotton, and are released in a variety of patterns.
Accessories
Vera Bradley makes coordinating accessories that include wallets, coin purses, clutches, tech cases, checkbook covers, cosmetic cases, glasses cases, wristlets, ID cases, and business card holders. The accessories are available in all of the Signature Cotton patterns.
Travel
The Vera Bradley Travel Collection includes Classic Cotton duffel/travel bags (made from the same fabric as the traditional handbags and accessories), as well as rolling luggage. The rolling luggage pieces come in Classic Black, Java Blue, and Yellow Bird, and prices range from 180 to 300 dollars.
Microfiber
Along with the Signature Cotton collection, Vera Bradley releases a Microfiber line during the same period new patterns are released. Microfiber lines are released twice a year, each time with different style bags, detail stitching, and inside prints. In previous collections, there have been handbags, laptop totes, tech cases, wristlets, backpacks, and overnight bags. The company has released brown and black Microfiber pieces; most recently, they created a black line for the Spring 09 collection that involved Electric Blue and Charcoal stitching.
Stationery
The stationery collection includes pencils, notepads, binders, notebooks and stationery cards made in association. All of the products are in the Vera Bradley classic cotton patterns. Recently, the stationary line has become popular as a supplement to backpacks and school totes for younger, middle school aged girls.
Limited Editions
Vera Bradley has also come out with many limited edition accessories. Some of the limited editions include the pet collection, the Seaside Collection, the Tropical Silk Collection, the Jacquard Line, the 25th Anniversary Collection, and more. Beach totes, towels, evening bags, dog carriers, and umbrellas are just some of the many products offered from these lines. The new Resort Collection, featuring Mediterranean White and Blue, is a separate line within the Signature Cotton; however, they are not limited edition prints. This collection was released in September 2008. In addition to the Mediterranean White and Blue, which come in all of the Signature Collection pieces, the Mosaic print (the inside pattern of Mediterranean Blue) is available in a specific few accessory pieces.
The Vera Bradley Foundation
The Vera Bradley Foundation supports Breast Cancer Research. Sales from the Pink Elephants (retired in June 08), Pinwheel Pink (launched January 08), and Hope Garden (launched January 09) prints benefit the organization.
The company was founded in March 1982 by Patricia Miller and Barbara Bradley Baekgaard, a 1962 graduate of Marymount College. Named after Baekgaard's mother, the company got its start when both were inspired while awaiting a flight in Atlanta, where they noticed a "definite lack of feminine-looking luggage".
Products
A Peacock-patterned Vera Bradley bag.
Vera Bradley bags come in many sizes and styles, as well as many different patterns and colors. There are travel duffels, medium sized totes, large totes, purses, wallets, eyeglass and sunglass cases, cosmetic cases, and jewelry cases. There are also umbrellas, napkins, placemats, rolling luggage, tableware, bedding, fine rugs, accessory coverings, and stationery. Pet collars, beds, leashes, and carriers for small dogs, cats, and rabbits were also available for a limited time. The purses come with a variety of names such as the Vera, the Bucket Tote, and the Audrey. After a pattern is on the market for a while, the company retires it. When patterns retire, new ones are produced. New patterns are released in spring and fall colors; they are typically introduced in January and July. The company will also retire or redesign specific styles and new styles may be introduced in concurrence with the new patterns.
Within the past few years, Vera Bradley has become increasingly popular with many women for a variety of reasons. Compared to other, more expensive handbag lines, Vera Bradley offers an affordable yet stylish solution to the search for an everyday handbag. The bags are handy and useful, many with multiple pockets inside and outside the bag. Furthermore, all handbags/totes/travel bags are washable, as long as the cardboard base is removed. Accessories and Microfiber lines can be spot cleaned. Overall, the product is successful due to its lightweight, comfortable, and attractive feel. With over 15 patterns available at any given time, there is a pattern and bag style to appeal to every woman.
Collections
All collections are available in a variety of colors and patterns.
Patterns
The following patterns are active patterns, currently available in all Vera Bradley Signature Stores and Retailers:
Hope Garden, Purple Punch, Cupcakes Green, and Cupcakes Pink, released Jan. 09.
Mediterranean Blue, Mediterranean White, and Mosaic, released Sept. 08.
Frankly Scarlet, Caffe Latte, Puccini, and Night Owl, released June 08.
Raspberry Fizz, Daisy Daisy, Yellow Bird, and Pinwheel Pink, released Jan. 08.
Mod Floral Pink and Mod Floral Blue, released July 07.
Java Blue, released Jan. 06. *Java Blue is the longest running pattern in Vera Bradley history*
Vera Bradley makes dozens of different types of handbags ranging from wristlets to large totes. Some names include the Amy, the Hipster, the Tote, the Morgan, the Hannah, the Betsy and the Villager. The handbags are made out of washable quilted cotton, and are released in a variety of patterns.
Accessories
Vera Bradley makes coordinating accessories that include wallets, coin purses, clutches, tech cases, checkbook covers, cosmetic cases, glasses cases, wristlets, ID cases, and business card holders. The accessories are available in all of the Signature Cotton patterns.
Travel
The Vera Bradley Travel Collection includes Classic Cotton duffel/travel bags (made from the same fabric as the traditional handbags and accessories), as well as rolling luggage. The rolling luggage pieces come in Classic Black, Java Blue, and Yellow Bird, and prices range from 180 to 300 dollars.
Microfiber
Along with the Signature Cotton collection, Vera Bradley releases a Microfiber line during the same period new patterns are released. Microfiber lines are released twice a year, each time with different style bags, detail stitching, and inside prints. In previous collections, there have been handbags, laptop totes, tech cases, wristlets, backpacks, and overnight bags. The company has released brown and black Microfiber pieces; most recently, they created a black line for the Spring 09 collection that involved Electric Blue and Charcoal stitching.
Stationery
The stationery collection includes pencils, notepads, binders, notebooks and stationery cards made in association. All of the products are in the Vera Bradley classic cotton patterns. Recently, the stationary line has become popular as a supplement to backpacks and school totes for younger, middle school aged girls.
Limited Editions
Vera Bradley has also come out with many limited edition accessories. Some of the limited editions include the pet collection, the Seaside Collection, the Tropical Silk Collection, the Jacquard Line, the 25th Anniversary Collection, and more. Beach totes, towels, evening bags, dog carriers, and umbrellas are just some of the many products offered from these lines. The new Resort Collection, featuring Mediterranean White and Blue, is a separate line within the Signature Cotton; however, they are not limited edition prints. This collection was released in September 2008. In addition to the Mediterranean White and Blue, which come in all of the Signature Collection pieces, the Mosaic print (the inside pattern of Mediterranean Blue) is available in a specific few accessory pieces.
The Vera Bradley Foundation
The Vera Bradley Foundation supports Breast Cancer Research. Sales from the Pink Elephants (retired in June 08), Pinwheel Pink (launched January 08), and Hope Garden (launched January 09) prints benefit the organization.
History of quilting
Quilting at the dawn of the nineteenth century
Quilt making was uncommon in America in the late eighteenth century and early years of the nineteenth. Most women were busy spinning, weaving and sewing in order to clothe their family. Commercial blankets or woven coverlets were a more economical bedcovering for most people. Only the wealthy had the leisure time for quilt making so Colonial quilting was done by only a few.
Obviously quilts were not made of left over scraps or worn clothing as a humble bedcovering during this period. Instead they were decorative items that displayed the fine needlework of the maker.
Whole cloth quilts, broderie perse and medallion quilts were the styles of quilts made during the early 1800s.
Whole cloth quilt
Quilts made of a solid piece of fabric are referred to as Whole Cloth Quilts. The three layers of top, batting and backing were quilted together. The quilting itself became the decoration.
Both wool and cotton solid color quilts and white quilts were made during this period. The white ones are sometimes called "whitework".
A few were made with a simple overall quilting design but many were works of art with beautiful quilting including feathers, flowers and other natural motifs. Some were made even more exquisite by a method called trapunto. Trapunto is the technique of slipping extra stuffing into certain areas of a quilt to bring out the quilting in that area. For example trapunto can make the area inside a feather or flower making that part of the quilt a little thicker. Women were proud of fine and even quilt stitches in these quilts
Broderie perse quilts
Broderie perse refers to the applique of cut out motifs from printed fabric onto a solid background. This form of quilt making has been done since the 18th century. The popular printed fabric during this period was chintz imported from India.
Printed fabric was expensive even for those who were well off. By cutting out birds, flowers and other motifs from printed fabric and sewing them onto a large homespun cloth a beautiful bedspread could be made. The technique was also used on some early medallion quilts as in the example linked below.
Broderie Perse bedcoverings were usually used on the best bed or sometimes only when guests were staying in the home.
Medallion quilts
Medallion quilts are made around a center. The center was sometimes a solid piece of large scale fabric like a toile or a Tree of Life, an appliqued motif or a large pieced star or other pieced pattern. The central area was surrounded by two or more borders. Although some borders were solid, many were pieced or appliqued.
Changes in quiltmaking during the mid nineteenth century
Progress in technology deeply affected the number and styles of quilts made during the middle years of the 1800s.
The industrial revolution brought about the most dramatic change as textiles came to be manufactured on a broad scale. This meant women no longer had to spend time spinning and weaving to provide fabric for their family’s needs. By the 1840s the textile industry had grown to the point that commercial fabrics were affordable to almost every family. As a result quilt making became widespread.
A great variety of cotton prints could be bought for the making of clothing and even specifically for making a quilt. Although scraps left over from dressmaking and other sewing projects were used in quilt making, it is a myth that quilts were always made from scraps and worn out clothing. Examining pictures of quilts found in museums we quickly see that many quilts were made with fabric bought specifically for that quilt.
Another major shift was in the style of quilts made. Although a few earlier quilts were made in the block style, quilts made up of blocks were uncommon until around the 1840s. With so many fabrics being manufactured quilters could create their blocks with a delightful variety of fabrics.
Some block style quilts were made of a set of identical pieced blocks while others contained a variety of blocks made with different patterns. The blocks were sewn together and a border may or may not have been added.
During this period the invention and availability of the sewing machine contributed to quilt making. In 1856 The Singer company started the installment plan so that more families could afford a sewing machine. By the 1870s a good many households owned a sewing machine.
This affected quilt making in two ways. First of all women could make clothing for their family in much less time leaving more time for quilt making and secondly they could use their sewing machines to make all or part of their quilts. More often the sewing machine was used to piece quilts but occasionally the quilting was done with the sewing machine.
Two types of signature quilts
One significant type of quilt made during this period were signature quilts. Indelible ink was available after 1840 making it possible to not only sign a quilt but to add inscriptions including poetry, personal messages or other information. The more elaborate autographs and inscriptions are seen most often in quilts made before the Civil War.
We refer to quilts in which all the blocks were the same pattern as friendship quilts. Often each person made a block and signed it. Other times one person made the quilt then each person signed a block. Sometimes a person with exceptional handwriting inscribed all the signatures. There was no single way that friendship quilts were made.
Friendship quilts had special meaning for those who were traveling westward as they could look at the quilt and remember friends and family left behind.
The other kind of autograph quilt was the album quilt that consisted of several unique quilt blocks. More often these album blocks were appliquéd while the friendship quilts were usually made up of pieced blocks. The most elegant of thes album autograph quilts were Baltimore album quilts.
Baltimore album quilts originated in Baltimore, Maryland in the 1840s. These album quilts of lovely appliquéd blocks were sometimes designed by the maker though in time patterns by accomplished designers were used as the popularity of this quilt style spread. They reflected the prosperous community of Baltimore as most were made not with scraps but with new fabric.
Quilting for the cause in the United States during the Civil War era
There were many years and events leading up to the American Civil War. First quilts were made to raise funds to support the abolitionist movement then during the Civil War quilts were made to earn money for the war effort and to give warmth and comfort to soldiers. The patterns were much like those made mid-century but the purpose was different. Quilts connected to the abolitionist movement and the Civil War were made for a cause.
The movement to free the slaves and the role of quilts
Even before 1830 abolitionists were working hard to end slavery. One way they did this was to hold grand fairs to raise both awareness and money for the abolitionist cause. Quilts were one of many craft pieces sold at these fairs. These quilts were usually fine quilts often with beautiful appliqué. Women sometimes put anti-slavery poems and sayings on the quilts they made for fairs as well as for friends and family. The goal was to show the terrible plight of the slaves.
Some abolitionists were active in the Underground Railroad helping runaway slaves get to safety. There are stories that certain quilts were used as signals to help the slaves in their flight to freedom. The idea that a log cabin quilt would be hung on the line of a safe house was one. More recent stories tell of certain quilts being used to tell the slaves what they needed to do to get to safety. This all sounds quite romantic but there is no historic evidence that quilts were ever used in this way. But we do know that a valiant effort was made by both whites and free slaves to help these slaves to their destination.
Quilt historians have written about the lack of evidence that Quilts of the Underground Railroad were any more than stories that have caught our imagination.
Quilts to warm the soldiers and quilts to raise money for the war
Women on both sides were very active in raising money for the war effort and making quilts and other bed coverings for soldiers.
In the north quilts were still made for fairs but now these fairs earned money to support needs that came about because of the war. In the south lovely quilts called gun boat quilts were made to pay for much needed gun boats.
But it wasn't long before it was obvious that soldiers on both sides would need blankets and quilts to give them warmth. In the north women either made quilts or remade quilts from bed coverings. Since the cots were narrow two bedspreads could be made into three quilts for soldiers. The United States Sanitary Commission was in charge of collecting these quilts and distributing them.
In the south it was more difficult. Even though cotton was grown in the south it was manufactured into fabric in the north. Before long fabric was almost impossible to obtain so women had to spin and weave before they could sew together a bed covering.
Needless to say most of the quilts made for soldiers on either side were made with practical patterns and fabric. Very few have survived to this day.
Quilting During the last decades of the 19th century, the Victorian Era
Quilt making continued to be a popular craft during the latter part of the 1800s. The Victorian influence was a bit delayed in the United States because of the Civil War and it's aftermath.
The Crazy Quilting Fad
In terms of quilts the latter years of the nineteenth century the best know quilt style was the Crazy Quilt. Crazy quilts were made of abstract shapes sewn together. Usually the quilt maker then used embroidery to embellish the quilt. First fancy stitches were sewn along the seams. Often the maker also added embroidered motifs including flowers, birds and sometimes a spider and web for good luck. Crazy quilting was quite the fad during this period. Magazines encouraged making crazies. Young women were particularly eager to make them. These quilts were seldom used as bedcoverings. Instead they were made smaller and without batting to be used as decorative throws.
Traditional Quilts Were Still Made
Because the crazy quilting craze was so popular during this period one might overlook the fact that many traditional quilts were also made. Utilitarian quilts were pieced and tied or simply quilted for everyday bed coverings while beautiful pieced and/or appliquéd quilts were created for special events like a wedding or when a beloved minister was transferred to a new location. These were more often elaborately quilted.
Urinal
Flushing
Most public urinals incorporate a flushing system to rinse urine from the bowl of the device to prevent foul odors. The flush can be triggered by one of several methods:
Manual handles
This type of flush might be regarded as standard in the United States. Each urinal is equipped with a button or short lever to activate the flush, with users expected to operate it as they leave. Such a directly-controlled system is the most efficient provided that patrons remember to use it. This is far from certain, however, often because of fear of touching the handle, which is located too high to kick. Urinals with foot-activated flushing systems are sometimes found in high-traffic areas; these systems have a button set into the floor or a pedal on the wall at ankle height. Some establishments, often bars, pubs, or nightclubs, fill their urinals with ice cubes during peak hours. As the ice melts, it serves to slowly flush the urinal, and also cools the urine to prevent smells from rising during use. The Americans with Disabilities Act requires that flush valves be mounted no higher than 44 in AFF (above the finished floor). Additionally, the urinal shall be mounted no higher than 17 in AFF, which has a rim that is tapered and elongated and protrudes at least 14 in from the wall. This enables users in wheelchairs to straddle the lip of the urinal and urinate without having to "arc" the flow of urine too high.
In some regions of Japan, particularly the industrial zones of Honshū, many urinals feature a voice-activated flushing system. These flush systems are triggered by the word "wash!", "fire" or "destroy the grime" in over 30 different languages.
Timed flush
A multi-person urinal in Chung Ling High School, Malaysia, operated using timed-flush mechanism.
In Germany, the United Kingdom, France, Ireland, Canada ,Hong Kong and some parts of Sweden and Finland, manual flush handles are unusual. Instead, the traditional system is a timed flush that operates automatically at regular intervals. Groups of up to ten or so urinals will be connected to a single overhead cistern, which contains the timing mechanism. A constant drip-feed of water slowly fills the cistern, until a tripping point is reached, the valve opens (or a siphon begins to drain the cistern), and all the urinals in the group are flushed. Electronic controllers performing the same function are also used.
This system does not require any action from its users, but it is wasteful of water where the toilets are used irregularly. However, in these countries men are so used to the automatic system, attempts to install manual flushes to save water are generally unsuccessful. Users ignore them not through deliberate laziness or fear of infection, but because activating the flush is not habitual.
To help reduce water usage when restrooms are closed, some restrooms with timed flushing use an electric water valve connected to the restroom light switch. When the building is in active use during the day and the lights are on, the timed flush operates normally. At night when the building is closed, the lights are turned off and the flushing action stops.
A flushing system connected to the opening of the washroom door can count the number of users and operate when the count reaches a certain value. At night, the door never opens, so flushing never occurs.
Toto battery-powered hands-free automatic sensor operated flush system.
Electronic automatic flushes solve the problems of both previous approaches, and are common in new installations. Active or (more usually) passive infrared sensors identify when the urinal has been used (or when someone has stood in front of it and moved away), and activate the flush. Thus the urinal is cleaned, where with a manual flush it might not have been, but water is not wasted when the toilet is not used.
Automatic flush facilities can be retrofitted to existing systems. The handle-operated valves of a manual system can be replaced with a suitably-designed self-contained electronic valve, often battery-powered to avoid the need to add cables. Timed-flush installations may add a device that regulates the water flow to the cistern according to the overall activity detected in the room. This does not provide true per-fixture automatic flushing, but is simple and cheap to add because only one device is required for the whole system.
To prevent false-triggering of the automatic flush, most infra-red detectors require that a presence be detected for at least five seconds, such as when a person is standing in front of it. This prevents a whole line of automatic flush units from triggering in series if someone just walks past them.
The automatic flush mechanism also typically waits for the presence to go out of sensor range before flushing. This reduces water usage, compared to a sensor that would trigger a continuous flushing action all the while a presence is being detected.
Door-regulated flush
This is an older method of water-saving automatic flushing, which only operates when the room is being used. A push-button switch is mounted in the door frame of the restroom, and triggers the flush valve for all restroom urinals every time the door is opened. While it can't detect the use of individual urinals, it provides reasonable flushing action without wasting excessive amounts of water when the restroom is not being used. This method requires a spring-operated automatic door closer, since the flush mechanism only operates when the restroom door opens.
Waterless urinals
A waterless urinal by Armitage Shanks (UK)
A more recent innovation is urinals that do not use water at all. Models introduced by Waterless Company in 1992 and others in 2001 by Falcon Waterfree Technologies and Sloan Valve Company, as well as Duravit, utilize a trap insert filled with a sealant liquid instead of water. The lighter-than-water sealant floats on top of the urine collected in the U-bend, preventing odors from being released into the air. Although the cartridge and sealant must be periodically replaced, the system saves anywhere between 15,000 and 45,000 gallons (approx. between 56,800 and 170,000 liters) of water per urinal per year. Other companies do not use a cartridge; instead they have developed an outlet system that traps the odor, preventing the smell often present in toilet blocks. They can be installed in high-traffic facilities and in situations where providing a water supply may be difficult or where water conservation is desired. Due to high-level water restrictions, Brisbane has mandated conversion to waterless urinals and flush urinals are rarely seen.
In March 2006, the Associated Press reported that the plumbers union in Philadelphia had become upset because the developer of the city's newest skyscraper, Liberty Property Trust, has decided to use waterless urinals in the Comcast Center. Many in the union decided that because of the decision that this would lead to less work for them. The developer cited saving the city 1.6 million gallons (approx 6.06 million liters) of water per year as its deciding factor
Arrangement of urinals
A typical arrangement of urinals, in a linear array, without partitions: a row of sensor operated fixtures provides for optimal traffic flow and throughput.
Urinals in high capacity men's washrooms are usually arranged in one or more rows. Those in the street may come in sets arranged in a circle, with all men facing the center, with screens high enough that men cannot wet each other, and usually high enough that they cannot see over it. In a street urinal with an outside screen or wall, the men may stand back to back.
Urinals used for high throughput capacity are part of an efficiently designed washroom architecture. Large numbers of them are usually installed along a common supply pipe and drain. There may be partitions for privacy.
A portable set of four urinals in the Netherlands.
Often, one or two of the urinals, typically at one end of a long row of urinals, will be mounted lower than the others; they are meant for young boys and other males who cannot reach the regular urinals. In facilities where males of various heights are present, such as schools, urinals that extend down to floor level may be used to allow anyone of any height to use any urinal.
Once used exclusively in commercial or institutional washrooms, urinals for private home installation are now available. They offer the advantage of substantial savings of water in homes with multiple male occupants.
Street urinals and vespasiennes
In some localities, urinals may be located on public sidewalks or in public areas such as parks. These urinals are usually equipped with partitions for the sake of privacy. They may or may not be equipped with flush mechanisms.
The last surviving vespasienne, on the boulevard Arago in Paris
A city famous for its street urinals is Paris, France. Until the 1990s, street urinals were a common sight in the city, and in the 1930s more than 1200 were in service. Parisians referred to them as vespasiennes, the name being derived from that of the Roman Emperor Vespasian, who, according to an anecdote, imposed a tax on urine. Beginning in the 1990s, the vespasiennes (renowned for their smell and lack of hygiene) were gradually replaced by Sanisettes. Today only one vespasienne remains in the city (on the boulevard Arago), and it is still regularly used. They still exist in other French cities, and in other countries.
See also Public toilets.
Makeshift urinals
During the Korean War, Vietnam War, Operation Desert Storm etc., "piss tubes" were used as makeshift urinals.[citation needed] To make one, soldiers would affix an inverted water bottle on one end of a rigid tube, burying the other end. Removing the base of the bottle made a funnel which would be left at the proper height. Deposited urine simply soaked into the ground. When the area became saturated, the device was relocated.
Urinals for women
A modern female urinal at Dortmund Airport, Germany.
Nearly all urinals are intended for use by males, but a few have been designed for use by women. From 1950 to 1974, the American Standard company offered the mass-produced "Ladies' Home Urinal." It did not provide significant advantages over conventional toilets, because it used just as much floor space and flushing water. Its main selling point was that women could use the fixture without touching it.
Several other designs have been tried since then, but they either required the user to hover awkwardly or to bring her genitals into close contact with the fixture. Most have not caught on. Current clothes fashion such as panty hose and slacks inhibit women from using them because they don't want their garments to touch the urinals or the floor. Often, women have little experience with them and don't know whether to approach them forward or backward
A typical arrangement of urinals, in a linear array, without partitions: a row of sensor operated fixtures provides for optimal traffic flow and throughput.
Urinals in high capacity men's washrooms are usually arranged in one or more rows. Those in the street may come in sets arranged in a circle, with all men facing the center, with screens high enough that men cannot wet each other, and usually high enough that they cannot see over it. In a street urinal with an outside screen or wall, the men may stand back to back.
Urinals used for high throughput capacity are part of an efficiently designed washroom architecture. Large numbers of them are usually installed along a common supply pipe and drain. There may be partitions for privacy.
A portable set of four urinals in the Netherlands.
Often, one or two of the urinals, typically at one end of a long row of urinals, will be mounted lower than the others; they are meant for young boys and other males who cannot reach the regular urinals. In facilities where males of various heights are present, such as schools, urinals that extend down to floor level may be used to allow anyone of any height to use any urinal.
Once used exclusively in commercial or institutional washrooms, urinals for private home installation are now available. They offer the advantage of substantial savings of water in homes with multiple male occupants.
Street urinals and vespasiennes
In some localities, urinals may be located on public sidewalks or in public areas such as parks. These urinals are usually equipped with partitions for the sake of privacy. They may or may not be equipped with flush mechanisms.
The last surviving vespasienne, on the boulevard Arago in Paris
A city famous for its street urinals is Paris, France. Until the 1990s, street urinals were a common sight in the city, and in the 1930s more than 1200 were in service. Parisians referred to them as vespasiennes, the name being derived from that of the Roman Emperor Vespasian, who, according to an anecdote, imposed a tax on urine. Beginning in the 1990s, the vespasiennes (renowned for their smell and lack of hygiene) were gradually replaced by Sanisettes. Today only one vespasienne remains in the city (on the boulevard Arago), and it is still regularly used. They still exist in other French cities, and in other countries.
See also Public toilets.
Makeshift urinals
During the Korean War, Vietnam War, Operation Desert Storm etc., "piss tubes" were used as makeshift urinals.[citation needed] To make one, soldiers would affix an inverted water bottle on one end of a rigid tube, burying the other end. Removing the base of the bottle made a funnel which would be left at the proper height. Deposited urine simply soaked into the ground. When the area became saturated, the device was relocated.
Urinals for women
A modern female urinal at Dortmund Airport, Germany.
Nearly all urinals are intended for use by males, but a few have been designed for use by women. From 1950 to 1974, the American Standard company offered the mass-produced "Ladies' Home Urinal." It did not provide significant advantages over conventional toilets, because it used just as much floor space and flushing water. Its main selling point was that women could use the fixture without touching it.
Several other designs have been tried since then, but they either required the user to hover awkwardly or to bring her genitals into close contact with the fixture. Most have not caught on. Current clothes fashion such as panty hose and slacks inhibit women from using them because they don't want their garments to touch the urinals or the floor. Often, women have little experience with them and don't know whether to approach them forward or backward
More recently, models that use specialized funnels have been introduced, with some success, at outdoor festivals (to reduce cycle times and alleviate long lines).
Further information: Female urination device
Special urinals
"Kisses!" is a controversial urinal designed by the female Dutch designer Meike van Schijndel. It is shaped like an open pair of red lips.In early March of 2004 the National Organization for Women (NOW) took offense to these new urinals Virgin Atlantic Airways decided to install in the Virgin Atlantic clubhouse at JFK Airport in New York, New York. After receiving many angry phone calls from female customers Virgin Atlantic Vice President John Riordan called NOW to apologize. Protestors surmised a connection to oral sex and/or urolagnia, and based complaints on the urinals being sexist.
A McDonald's restaurant in the Netherlands removed them after a customer complained to the U.S. head office.
Fountain by Marcel Duchamp, 1917, photographed by Alfred Stieglitz at his 291 gallery after the 1917 Society of Independent Artists exhibit.
Marcel Duchamp's Fountain (1917) is one of the most influential pieces of modern art.
On January 27, 2004, inventor Eric D Page from Sarasota, Florida was granted U.S. Patent 6,681,419 for a "Forehead support apparatus". The abstract of the patent makes it clear that this is "...for resting a standing users forehead against a wall above a bathroom commode or urinal or beneath a showerhead." The abstract continues:
"The apparatus includes a mounting member adapted for attachment to an upright bathroom wall either above the commode or urinal or below the showerhead. A compressible head support member is attached to and extends from the wall and said mounting member. The head support defines an elastically deformable or resilient forehead support surface which is spaced above the floor and from the wall a distance sufficient for the user to lean his forehead thereagainst and be supported while using the commode or urinal."
Nassau County, New York Police adopted Talking Urinals in a unique Anti-Drunk Driving initiative. Utilizing Wizmark, a talking urinal screen, police can provide bars with free pre-programmed urinal screens urging patrons not to drink and drive.
The bullet damaged brick wall from the St. Valentines Day Massacre was disassembled where it had been originally constructed at 2122 N. Clark Street, Chicago, Illinois and reassembled in men's restroom of a bar called Banjo Palace in Vancouver, British Columbia where it served as a urinal wall.
Ernest Hemingway converted a urinal from Sloppy Joe's bar into a water fountain for his cats. The fountain remains a prominent feature at his former home in Key West, Florida; which remains a popular tourist destination in the city.
One example of urinals in popular culture was in a 1990 episode of the sitcom Roseanne. Roseanne Conner is dressed as a man for Halloween and is somehow forced into using a urinal. While doing so, she looks at and talks loudly to the men next to her, and when she gets silence and uncomfortable looks in return, she then looks straight ahead, and says: "Oh, I get it! It's like an elevator!" In the late 1990s, a similar gag was used on Third Rock from the Sun, when Sally Solomon and Dick Solomon switch bodies, and Sally (in Dick's body) has to use a urinal alongside Officer Don (Sally's boyfriend).
Some urinals for men incorporate fly targets: images of flies that are either printed on labels stuck to the inside of the urinal or embossed directly into the porcelain. Men often feel a compulsion to aim their urine stream at the fly, and thus the fly target helps prevent men from urinating outside the basin or bowl of the urinal. Maintenance crews at Schiphol airport in Amsterdam reported in 2005 that adding a fly target to urinals reduced bathroom cleaning costs by giving men something to aim at. The urinals at terminal 4 of John F. Kennedy International Airport in New York City have a fly target in the urinals. These are replaced every month because they slide off.
Urinals are mentioned briefly by George Carlin (Wikiquote) in his routine about sports, in which he comments, about ice hockey, that "the only other place you'll find a puck is in the urinal to control the smell in the bathroom." In an earlier album he relates how important it is to "wetdown" all the dry spots on the porcelain, and how Kent cigarettes with the Micronite filter are the hardest to break up by urinating on them - requiring "...three men and a keg of beer."
Pissoir, retitled Urinal in some countries, was the first feature film directed by John Greyson. It was released in 1980 and takes place in a toilet.
Gabriel Chevallier's 1934 satirical novel Clochemerle deals with the ramifications over plans to install a new urinal in a French village.
The aircraft manufacturer Airbus will be offering its customers the option of installing urinals in its A380 aircraft.
Further information: Female urination device
Special urinals
"Kisses!" is a controversial urinal designed by the female Dutch designer Meike van Schijndel. It is shaped like an open pair of red lips.In early March of 2004 the National Organization for Women (NOW) took offense to these new urinals Virgin Atlantic Airways decided to install in the Virgin Atlantic clubhouse at JFK Airport in New York, New York. After receiving many angry phone calls from female customers Virgin Atlantic Vice President John Riordan called NOW to apologize. Protestors surmised a connection to oral sex and/or urolagnia, and based complaints on the urinals being sexist.
A McDonald's restaurant in the Netherlands removed them after a customer complained to the U.S. head office.
Fountain by Marcel Duchamp, 1917, photographed by Alfred Stieglitz at his 291 gallery after the 1917 Society of Independent Artists exhibit.
Marcel Duchamp's Fountain (1917) is one of the most influential pieces of modern art.
On January 27, 2004, inventor Eric D Page from Sarasota, Florida was granted U.S. Patent 6,681,419 for a "Forehead support apparatus". The abstract of the patent makes it clear that this is "...for resting a standing users forehead against a wall above a bathroom commode or urinal or beneath a showerhead." The abstract continues:
"The apparatus includes a mounting member adapted for attachment to an upright bathroom wall either above the commode or urinal or below the showerhead. A compressible head support member is attached to and extends from the wall and said mounting member. The head support defines an elastically deformable or resilient forehead support surface which is spaced above the floor and from the wall a distance sufficient for the user to lean his forehead thereagainst and be supported while using the commode or urinal."
Nassau County, New York Police adopted Talking Urinals in a unique Anti-Drunk Driving initiative. Utilizing Wizmark, a talking urinal screen, police can provide bars with free pre-programmed urinal screens urging patrons not to drink and drive.
The bullet damaged brick wall from the St. Valentines Day Massacre was disassembled where it had been originally constructed at 2122 N. Clark Street, Chicago, Illinois and reassembled in men's restroom of a bar called Banjo Palace in Vancouver, British Columbia where it served as a urinal wall.
Ernest Hemingway converted a urinal from Sloppy Joe's bar into a water fountain for his cats. The fountain remains a prominent feature at his former home in Key West, Florida; which remains a popular tourist destination in the city.
One example of urinals in popular culture was in a 1990 episode of the sitcom Roseanne. Roseanne Conner is dressed as a man for Halloween and is somehow forced into using a urinal. While doing so, she looks at and talks loudly to the men next to her, and when she gets silence and uncomfortable looks in return, she then looks straight ahead, and says: "Oh, I get it! It's like an elevator!" In the late 1990s, a similar gag was used on Third Rock from the Sun, when Sally Solomon and Dick Solomon switch bodies, and Sally (in Dick's body) has to use a urinal alongside Officer Don (Sally's boyfriend).
Some urinals for men incorporate fly targets: images of flies that are either printed on labels stuck to the inside of the urinal or embossed directly into the porcelain. Men often feel a compulsion to aim their urine stream at the fly, and thus the fly target helps prevent men from urinating outside the basin or bowl of the urinal. Maintenance crews at Schiphol airport in Amsterdam reported in 2005 that adding a fly target to urinals reduced bathroom cleaning costs by giving men something to aim at. The urinals at terminal 4 of John F. Kennedy International Airport in New York City have a fly target in the urinals. These are replaced every month because they slide off.
Urinals are mentioned briefly by George Carlin (Wikiquote) in his routine about sports, in which he comments, about ice hockey, that "the only other place you'll find a puck is in the urinal to control the smell in the bathroom." In an earlier album he relates how important it is to "wetdown" all the dry spots on the porcelain, and how Kent cigarettes with the Micronite filter are the hardest to break up by urinating on them - requiring "...three men and a keg of beer."
Pissoir, retitled Urinal in some countries, was the first feature film directed by John Greyson. It was released in 1980 and takes place in a toilet.
Gabriel Chevallier's 1934 satirical novel Clochemerle deals with the ramifications over plans to install a new urinal in a French village.
The aircraft manufacturer Airbus will be offering its customers the option of installing urinals in its A380 aircraft.
Ethernet over twisted pair
Ethernet over twisted pair refers to the use of a pair of copper cables, twisted around each other, for the physical layer of an Ethernet network (that is, a network in which the Ethernet protocol is used in the data link layer). There are several different standards for a copper-based physical medium. The most widely used are 10BASE-T, 100BASE-TX, and 1000BASE-T (Gigabit Ethernet), running at 10 Mbit/s, 100 Mbit/s, and 1000 Mbit/s (1 Gbit/s) respectively. These three standards all use the same connectors. Higher speed implementations nearly always support the lower speeds as well, so that in most cases different generations of equipment can be freely mixed. They use 8 position modular connectors, usually (but incorrectly) called RJ45 in the context of Ethernet over twisted pair. The cables usually used are four-pair or above twisted pair cable. Each of the three standards support both full-duplex and half-duplex communication. According to the standards, they all operate over distances of 'up to 100 meters'.
The common names of the standards are derived from several aspects of the physical media. The number refers to the theoretical maximum transmission speed in megabits per second (Mbit/s). The BASE is short for baseband, meaning that there is no frequency-division multiplexing (FDM) or other frequency shifting modulation in use; each signal has full control of wire, on a single frequency. The T designates twisted pair cable, where the pairs of wires are twisted together for purposes of reducing crosstalk (FEXT and NEXT) when the pulsing direct current goes across the wires and creates electromagnetic induction effects. Where there are several standards for the same transmission speed, they are distinguished by a letter or digit following the T, such as TX. Some higher-speed standards use twin-axial cable, designated by CX.
Twisted-pair Ethernet standards are such that the majority of cables can be wired 'straight-through' (pin 1 to pin 1, pin 2 to pin 2 and so on), but others may need to be wired in the 'crossover' form (receive to transmit and transmit to receive).
10BASE-T and 100BASE-TX only require two pairs to operate, pins 1 and 2 (transmit or TX), and pins 3 and 6 (receive or RX). Since 10BASE-T and 100BASE-TX need only two pairs and Category 5 cable has four pairs, it is possible, but not standard, to run two network connections (or a network connection and two phone lines) over a Cat 5 cable by using the normally unused pairs in these 10 and 100 Mbit/s configurations. This is not possible with 1000BASE-T since it requires all four pairs to operate, pins 1 and 2, 3 and 6 — as well as 4 and 5, 7 and 8.
It is conventional to wire cables for 10 or 100 Mbit/s Ethernet to either the T568A or T568B standards. Since these standards differ only in that they swap the positions of the two pairs used for transmitting and receiving (TX/RX). A cable with TIA-568A wiring at one end and TIA-568B wiring at the other is referred to as a crossover cable. The terms used in the explanations of the 568 standards, tip and ring, refer to older communication technologies, and equate to the positive and negative parts of the connections.
A 10BASE-T node (such as a PC) that transmits on pins 1 and 2 and receives on pins 3 and 6 to a network device is most often on a "straight-through" cable in the "MDI" wiring pattern where RX goes to RX and TX goes to TX. A straight-through cable is usually used to connect a node to its network device. In order for two network devices or two nodes to communicate with each other (such as a switch to another switch or computer to computer) a crossover cable is often required at speeds of 10 or 100 Mbit/s. If available, connections can be made with a straight-through cable by means of an "MDI-X" port, also known as an “internal crossover” or “embedded crossover” connection. Hub and switch ports with such internal crossovers are usually labelled as such, with "uplink" or “X”. For example, 3Com usually labels their ports 1X, 2X, and so on.
To connect two computers directly together without a switch, an Ethernet crossover cable is often used. Although many modern Ethernet host adapters can automatically detect another computer connected with a straight-through cable and then automatically introduce the required crossover, if needed; if one or neither of the computers does not, then a crossover cable is required. If both devices being connected support 1000BASE-T according to the standards, they will connect regardless of the cable being used or how it is wired.
To connect two hubs or switches directly together, a crossover cable can be used, but some hubs and switches have an “uplink” port used to connect network devices together, or have a way to manually select MDI or MDI-X on a single port so that a straight-through cable can connect that port to another switch or hub. Most newer switches have automatic crossover ("auto MDI-X" or "auto-uplink") on all ports, eliminating the uplink port and the MDI/MDI-X switch, and allowing all connections to be made with straight-through cables.
A 10BASE-T transmitter sends 2 differential voltages, +2.5 V or -2.5 V.
100BASE-TX follows the same wiring patterns as 10BASE-T but is more sensitive to wire quality and length, due to the higher bit rates.
A 100BASE-TX transmitter sends 3 differential voltages, +1 V, 0 V, or -1 V.
1000BASE-T uses all four pairs bi-directionally and the standard includes auto MDI-X; however, implementation is optional. With the way that 1000BASE-T implements signaling, how the cable is wired is immaterial in actual usage. The standard on copper twisted pair is IEEE 802.3ab for Cat 5e UTP, or 4D-PAM5; 4 dimensions using PAM (pulse amplitude modulation) with 5 voltages, −2, −1, 0, +1, and +2 While +2 V to -2 V voltage may appear at the pins of the line driver, the voltage on the cable is nominally +1 V, +0.5 V, 0 V, -0.5 V and -1 V[3].
Unlike earlier Ethernet standards using broadband and coaxial cable, such as 10BASE5 (thicknet) and 10BASE2 (thinnet), 10BASE-T does not specify the exact type of wiring to be used but instead specifies certain "characteristics" which a cable must meet. This was done in anticipation of using 10BASE-T in existing twisted pair wiring systems that may not conform to any specified wiring standard. Some of the specified characteristics are attenuation, characteristic impedance, timing jitter, propagation delay, and several types of noise. Cable testers are widely available to check these parameters to determine if a cable can be used with 10BASE-T. These characteristics are expected to be met by 100 meters of 24-gauge unshielded twisted-pair cable, and 100 meters is the stated maximum length for baseband signal runs. However, with high quality cabling, cable runs of 150 meters or longer are often obtained and are considered viable by most technicians familiar with the 10BASE-T specification, though — as with all CSMA/CD network environments — the absolute limit on run length is determined by the size of the collision domain and cable quality. In reality, what meets the standards may not work, and those that do not meet the standards might work.
100BASE-TX and 1000BASE-T both require a minimum of Category 5 cable (5e or 6 with 1000 Mbit/s) and also specify a maximum cable length of 100 meters. Furthermore while 10BASE-T is more tolerant of poor wiring such as split pairs, poor terminations and even use of short sections of flat cable, 100BASE-T is not as much so, and 1000BASE-T is less tolerant still. Since testing of cable is often limited to checking if it works with Ethernet, running faster speeds over existing cable is often problematic. This problem is made worse by the fact that Ethernet's autonegotiation takes account only of the capabilities of the end equipment not of the cable in between.
Autonegotiation and duplex mismatch
Main article: Autonegotiation
Main article: Duplex mismatch
Many different modes of operations (10BASE-T half duplex, 10BASE-T full duplex, 100BASE-TX half duplex, ...) exist for Ethernet over twisted pair, and most network adapters are capable of different modes of operations. In 1995, a standard was released for allowing two network adapters connected to each other to negotiate the best possible shared mode of operation. The autonegotiation standard contained a mechanism for detecting the speed but not the duplex setting of Ethernet peers that did not use autonegotiation.
When two linked interfaces are set to different duplex modes, the effect of this duplex mismatch is a network that functions much slower than its nominal speed.
Duplex mismatch may be inadvertently caused when an administrator configures an interface to a fixed mode (e.g. 100 Mbit/s full duplex) and fails to configure the remote interface, leaving it set to autonegotiate. Then, when the autonegotiation process fails, half duplex is assumed by the autonegotiating side of the link.
The resulting duplex mismatch results in a dramatically slow network, in which many collisions, and especially late collisions occur on the interface set to half-duplex, and FCS errors are seen on the full-duplex side.
Gigabit Ethernet standards require autonegotiation to be on in order to operate.
The common names of the standards are derived from several aspects of the physical media. The number refers to the theoretical maximum transmission speed in megabits per second (Mbit/s). The BASE is short for baseband, meaning that there is no frequency-division multiplexing (FDM) or other frequency shifting modulation in use; each signal has full control of wire, on a single frequency. The T designates twisted pair cable, where the pairs of wires are twisted together for purposes of reducing crosstalk (FEXT and NEXT) when the pulsing direct current goes across the wires and creates electromagnetic induction effects. Where there are several standards for the same transmission speed, they are distinguished by a letter or digit following the T, such as TX. Some higher-speed standards use twin-axial cable, designated by CX.
Twisted-pair Ethernet standards are such that the majority of cables can be wired 'straight-through' (pin 1 to pin 1, pin 2 to pin 2 and so on), but others may need to be wired in the 'crossover' form (receive to transmit and transmit to receive).
10BASE-T and 100BASE-TX only require two pairs to operate, pins 1 and 2 (transmit or TX), and pins 3 and 6 (receive or RX). Since 10BASE-T and 100BASE-TX need only two pairs and Category 5 cable has four pairs, it is possible, but not standard, to run two network connections (or a network connection and two phone lines) over a Cat 5 cable by using the normally unused pairs in these 10 and 100 Mbit/s configurations. This is not possible with 1000BASE-T since it requires all four pairs to operate, pins 1 and 2, 3 and 6 — as well as 4 and 5, 7 and 8.
It is conventional to wire cables for 10 or 100 Mbit/s Ethernet to either the T568A or T568B standards. Since these standards differ only in that they swap the positions of the two pairs used for transmitting and receiving (TX/RX). A cable with TIA-568A wiring at one end and TIA-568B wiring at the other is referred to as a crossover cable. The terms used in the explanations of the 568 standards, tip and ring, refer to older communication technologies, and equate to the positive and negative parts of the connections.
A 10BASE-T node (such as a PC) that transmits on pins 1 and 2 and receives on pins 3 and 6 to a network device is most often on a "straight-through" cable in the "MDI" wiring pattern where RX goes to RX and TX goes to TX. A straight-through cable is usually used to connect a node to its network device. In order for two network devices or two nodes to communicate with each other (such as a switch to another switch or computer to computer) a crossover cable is often required at speeds of 10 or 100 Mbit/s. If available, connections can be made with a straight-through cable by means of an "MDI-X" port, also known as an “internal crossover” or “embedded crossover” connection. Hub and switch ports with such internal crossovers are usually labelled as such, with "uplink" or “X”. For example, 3Com usually labels their ports 1X, 2X, and so on.
To connect two computers directly together without a switch, an Ethernet crossover cable is often used. Although many modern Ethernet host adapters can automatically detect another computer connected with a straight-through cable and then automatically introduce the required crossover, if needed; if one or neither of the computers does not, then a crossover cable is required. If both devices being connected support 1000BASE-T according to the standards, they will connect regardless of the cable being used or how it is wired.
To connect two hubs or switches directly together, a crossover cable can be used, but some hubs and switches have an “uplink” port used to connect network devices together, or have a way to manually select MDI or MDI-X on a single port so that a straight-through cable can connect that port to another switch or hub. Most newer switches have automatic crossover ("auto MDI-X" or "auto-uplink") on all ports, eliminating the uplink port and the MDI/MDI-X switch, and allowing all connections to be made with straight-through cables.
A 10BASE-T transmitter sends 2 differential voltages, +2.5 V or -2.5 V.
100BASE-TX follows the same wiring patterns as 10BASE-T but is more sensitive to wire quality and length, due to the higher bit rates.
A 100BASE-TX transmitter sends 3 differential voltages, +1 V, 0 V, or -1 V.
1000BASE-T uses all four pairs bi-directionally and the standard includes auto MDI-X; however, implementation is optional. With the way that 1000BASE-T implements signaling, how the cable is wired is immaterial in actual usage. The standard on copper twisted pair is IEEE 802.3ab for Cat 5e UTP, or 4D-PAM5; 4 dimensions using PAM (pulse amplitude modulation) with 5 voltages, −2, −1, 0, +1, and +2 While +2 V to -2 V voltage may appear at the pins of the line driver, the voltage on the cable is nominally +1 V, +0.5 V, 0 V, -0.5 V and -1 V[3].
Unlike earlier Ethernet standards using broadband and coaxial cable, such as 10BASE5 (thicknet) and 10BASE2 (thinnet), 10BASE-T does not specify the exact type of wiring to be used but instead specifies certain "characteristics" which a cable must meet. This was done in anticipation of using 10BASE-T in existing twisted pair wiring systems that may not conform to any specified wiring standard. Some of the specified characteristics are attenuation, characteristic impedance, timing jitter, propagation delay, and several types of noise. Cable testers are widely available to check these parameters to determine if a cable can be used with 10BASE-T. These characteristics are expected to be met by 100 meters of 24-gauge unshielded twisted-pair cable, and 100 meters is the stated maximum length for baseband signal runs. However, with high quality cabling, cable runs of 150 meters or longer are often obtained and are considered viable by most technicians familiar with the 10BASE-T specification, though — as with all CSMA/CD network environments — the absolute limit on run length is determined by the size of the collision domain and cable quality. In reality, what meets the standards may not work, and those that do not meet the standards might work.
100BASE-TX and 1000BASE-T both require a minimum of Category 5 cable (5e or 6 with 1000 Mbit/s) and also specify a maximum cable length of 100 meters. Furthermore while 10BASE-T is more tolerant of poor wiring such as split pairs, poor terminations and even use of short sections of flat cable, 100BASE-T is not as much so, and 1000BASE-T is less tolerant still. Since testing of cable is often limited to checking if it works with Ethernet, running faster speeds over existing cable is often problematic. This problem is made worse by the fact that Ethernet's autonegotiation takes account only of the capabilities of the end equipment not of the cable in between.
Autonegotiation and duplex mismatch
Main article: Autonegotiation
Main article: Duplex mismatch
Many different modes of operations (10BASE-T half duplex, 10BASE-T full duplex, 100BASE-TX half duplex, ...) exist for Ethernet over twisted pair, and most network adapters are capable of different modes of operations. In 1995, a standard was released for allowing two network adapters connected to each other to negotiate the best possible shared mode of operation. The autonegotiation standard contained a mechanism for detecting the speed but not the duplex setting of Ethernet peers that did not use autonegotiation.
When two linked interfaces are set to different duplex modes, the effect of this duplex mismatch is a network that functions much slower than its nominal speed.
Duplex mismatch may be inadvertently caused when an administrator configures an interface to a fixed mode (e.g. 100 Mbit/s full duplex) and fails to configure the remote interface, leaving it set to autonegotiate. Then, when the autonegotiation process fails, half duplex is assumed by the autonegotiating side of the link.
The resulting duplex mismatch results in a dramatically slow network, in which many collisions, and especially late collisions occur on the interface set to half-duplex, and FCS errors are seen on the full-duplex side.
Gigabit Ethernet standards require autonegotiation to be on in order to operate.
2009年1月17日星期六
Air conditioner
History
Main article: Air conditioning#History
In 1820, British scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida. He hoped eventually to use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities. Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. His hopes for its success vanished soon afterward when his chief financial backer died; Gorrie did not get the money he needed to develop the machine. According to his biographer Vivian M. Sherlock, he blamed the "Ice King", Frederic Tudor, for his failure, suspecting that Tudor had launched a smear campaign against his invention. Dr. Gorrie died impoverished in 1855 and the idea of air conditioning faded away for 50 years.
Early commercial applications of air conditioning were manufactured to cool air for industrial processing rather than personal comfort. In 1902 the first modern electrical air conditioning was invented by Willis Haviland Carrier in Syracuse, NY. Designed to improve manufacturing process control in a printing plant, his invention controlled not only temperature but also humidity. The low heat and humidity were to help maintain consistent paper dimensions and ink alignment. Later Carrier's technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of America was formed to meet rising demand. Over time air conditioning came to be used to improve comfort in homes and automobiles. Residential sales expanded dramatically in the 1950s.
In 1906, Stuart W. Cramer of Charlotte, North Carolina, was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning", using it in a patent claim he filed that year as an analogue to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company. This evaporation of water in air, to provide a cooling effect, is now known as evaporative cooling.
The first air conditioners and refrigerators employed toxic or flammable gases like ammonia, methyl chloride, and propane which could result in fatal accidents when they leaked. Thomas Midgley, Jr. created the first chlorofluorocarbon gas, Freon, in 1928. The refrigerant was much safer for humans but was later found to be harmful to the atmosphere's ozone layer. Freon is a trademark name of DuPont for any Chlorofluorocarbon (CFC), Hydrogenated CFC (HCFC), or Hydrofluorocarbon (HFC) refrigerant, the name of each including a number indicating molecular composition (R-11, R-12, R-22, R-134A). The blend most used in direct-expansion home and building comfort cooling is an HCFC known as R-22. It is to be phased out for use in new equipment by 2010 and completely discontinued by 2020. R-12 was the most common blend used in automobiles in the US until 1994 when most changed to R-134A. R-11 and R-12 are no longer manufactured in the US, the only source for purchase being the cleaned and purified gas recovered from other air conditioner systems. Several non-ozone depleting refrigerants have been developed as alternatives, including R-410A, known by the brand name Puron.
Innovation in air conditioning technologies continue, with much recent emphasis placed on energy efficiency and improving indoor air quality. As an alternative to conventional refrigerants, natural alternatives like CO2 (R-744) have been proposed
Refrigeration cycle
A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor.
In the refrigeration cycle, a heat pump transfers heat from a lower-temperature heat source into a higher-temperature heat sink. Heat would naturally flow in the opposite direction. This is the most common type of air conditioning. A refrigerator works in much the same way, as it pumps the heat out of the interior into the room in which it stands.
This cycle takes advantage of the way phase changes work, where latent heat is released at a constant temperature during a liquid/gas phase change, and where varying the pressure of a pure substance also varies its condensation/boiling point.
The most common refrigeration cycle uses an electric motor to drive a compressor. In an automobile, the compressor is driven by a belt over a pulley, the belt being driven by the engine's crankshaft (similar to the driving of the pulleys for the alternator, power steering, etc.). Whether in a car or building, both use electric fan motors for air circulation. Since evaporation occurs when heat is absorbed, and condensation occurs when heat is released, air conditioners use a compressor to cause pressure changes between two compartments, and actively condense and pump a refrigerant around. A refrigerant is pumped into the cooled compartment (the evaporator coil), where the low pressure causes the refrigerant to evaporate into a vapor, taking heat with it. In the other compartment (the condenser), the refrigerant vapor is compressed and forced through another heat exchange coil, condensing into a liquid, rejecting the heat previously absorbed from the cooled space.
Humidity
Air conditioning equipment usually reduces the humidity of the air processed by the system. The relatively cold (below the dew point) evaporator coil condenses water vapor from the processed air, much like a cold drink will condense water on the outside of a glass. The water is drained, removing water vapor from the cooled space and thereby lowering its relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In food retail establishments, large, open chiller cabinets act as highly effective dehumidifiers.
Some air conditioning units dry the air without cooling it. These work like a normal air conditioner, except that a heat exchanger is placed between the intake and exhaust. In combination with convection fans, they achieve a similar level of comfort as an air cooler in humid tropical climates, but only consume about one-third the energy. They are also preferred by those who find the draft created by air coolers uncomfortable.
Refrigerants
Main article: Refrigerant
"Freon" is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties. Unfortunately, evidence has accumulated that these chlorine-bearing refrigerants reach the upper atmosphere when they escape. Once the refrigerant reaches the stratosphere, UV radiation from the Sun cleaves the chlorine-carbon bond, yielding a chlorine radical. These chlorine atoms catalyze the breakdown of ozone into diatomic oxygen, depleting the ozone layer that shields the Earth's surface from strong UV radiation. Each chlorine radical remains active as a catalyst unless it binds with another chlorine radical, forming a stable molecule and breaking the chain reaction. CFC refrigerants in common but decreasing usage include R-11 and R-12. Newer and more environmentally-safe refrigerants such as HCFCs (R-22, used in most homes today) and HFCs (R-134a, used in most cars) have replaced most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hydrofluorocarbons (HFCs) such as R-410A, which lack chlorine.
The external section of a typical single-room air conditioning unit. For ease of installation, these are frequently placed in a window. This one was installed through a hole cut in the wall.
The internal section of the above unit. The front panel swings down to reveal the controls.
Internal section of a modern Americool window air conditioner.
Types of air conditioner equipment
Window and through-wall units
Many traditional air conditioners in homes or other buildings are single rectangular units used to cool all or a portion of an apartment, house, or other building. Hotels frequently use PTAC systems, which combine heating and air conditioning into the same unit. Air conditioner units need to have access to the space they are cooling (the inside) and a heat sink; normally outside air is used to cool the condenser section. For this reason, single unit air conditioners are placed in windows or through openings in a wall made for the air conditioner; the latter type includes portable air conditioners.
Window and through-wall units have vents on both the inside and outside, so inside air to be cooled can be blown in and out by a fan in the unit, and outside air can also be blown in and out by another fan to act as the heat sink. The controls are on the inside.
A large house or building may have several such units. Should virtually every room be cooled with its own air conditioning unit, most of the day, it would be less expensive to use central air conditioning, though that may not be physically possible.
Evaporative coolers
Main article: Evaporative cooler
In very dry climates, evaporative coolers are popular for improving comfort during hot weather. This type of cooler is the dominant cooler used in Iran, which has the largest number of these units of any country in the world, causing some to referring to these units as "Persian coolers."[4] An evaporative cooler is a device that draws outside air through a wet pad, such as a large sponge soaked with water. The sensible heat of the incoming air, as measured by a dry bulb thermometer, is reduced. The total heat (sensible heat plus latent heat) of the entering air is unchanged. Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite comfortable. These coolers cost less and are mechanically simple to understand and maintain.
An early type of cooler, using ice for a further effect, was patented by John Gorrie of Apalachicola, Florida in 1842. He used the device to cool the patients in his malaria hospital.
Absorptive chillers
Main article: Absorption refrigerator
Central air conditioning
Central air conditioning, commonly referred to as central air (U.S.) or air-con (UK), is an air conditioning system which uses ducts to distribute cooled and/or dehumidified air to more than one room, or uses pipes to distribute chilled water to heat exchangers in more than one room, and which is not plugged into a standard electrical outlet.
With a typical split system, the condenser and compressor are located in an outdoor unit; the evaporator is mounted in the air handler unit. With a package system, all components are located in a single outdoor unit that may be located on the ground or roof.
Central air conditioning performs like a regular air conditioner but has several added benefits:
When the air handling unit turns on, room air is drawn in from various parts of the building through return-air ducts. This air is pulled through a filter where airborne particles such as dust and lint are removed. Sophisticated filters may remove microscopic pollutants as well. The filtered air is routed to air supply ductwork that carries it back to rooms. Whenever the air conditioner is running, this cycle repeats continually.
Because the central air conditioning unit is located outside the home, it offers a lower level of indoor noise than a free-standing air conditioning unit.
Thermostats
Main article: Thermostat
Thermostats control the operation of HVAC systems, turning on the heating or cooling systems to bring the building to the set temperature. Typically the heating and cooling systems have separate control systems (even though they may share a thermostat) so that the temperature is only controlled "one-way." That is, in cold weather, a building that is too hot will not be cooled by the thermostat. Thermostats may also be incorporated into facility energy management systems in which the power utility customer may control the overall energy expenditure. In addition, a growing number of power utilities have made available a device which, when professionally installed, will control or limit the power to an HVAC system during peak use times in order to avoid necessitating the use of rolling blackouts. The customer is given a credit of some sort in exchange, so it is often to the advantage of the consumer to buy the most efficient thermostat possible.
Equipment capacity
Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration." A "ton of refrigeration" is defined as the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. This is equal to 12,000 BTU per hour, or 3517 watts.Residential central air systems are usually from 1 to 5 tons (3 to 20 kilowatts (kW)) in capacity.
The use of electric/compressive air conditioning puts a major demand on the electrical power grid in warm weather, when most units are operating under heavy load. In the aftermath of the 2003 North America blackout locals were asked to keep their air conditioning off. During peak demand, additional power plants must often be brought online, usually expensive peaker plants. A 1995 meta-analysis of various utility studies concluded that the average air conditioner wasted 40% of the input energy. This energy is lost in the form of heat, which must be pumped out. There is a huge opportunity to reduce the need for new power plants and to conserve energy.
In an automobile, the A/C system will use around 5 horsepower (4 kW) of the engine's power.
Seasonal Energy Efficiency Rating (SEER)
Main article: Seasonal Energy Efficiency Rating
For residential homes, some countries set minimum requirements for energy efficiency. In the United States, the efficiency of air conditioners is often (but not always) rated by the Seasonal Energy Efficiency Ratio (SEER). The higher the SEER rating, the more energy efficient is the air conditioner. The SEER rating is the BTU of cooling output during its normal annual usage divided by the total electric energy input in watt hours (W·h) during the same period.
SEER = BTU ÷ W·h
For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, operating for a total of 1000 hours during an annual cooling season (i.e., 8 hours per day for 125 days) would provide an annual total cooling output of:
5000 BTU/h × 1000 h = 5,000,000 BTU
which, for a SEER of 10, would be an annual electrical energy usage of:
5,000,000 BTU ÷ 10 = 500,000 W·h
and that is equivalent to an average power usage during the cooling season of:
500,000 W·h ÷ 1000 h = 500 W
SEER is related to the coefficient of performance (COP) commonly used in thermodynamics and also to the Energy Efficiency Ratio (EER). The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures, while SEER is calculated over a whole range of external temperatures (i.e., the temperature distribution for the geographical location of the SEER test). SEER is unusual in that it is composed of an Imperial unit divided by an SI unit. The COP is a ratio with the same metric units of energy (joules) in both the numerator and denominator. They cancel out, leaving a dimensionless quantity. Formulas for the approximate conversion between SEER and EER or COP are available from the Pacific Gas and Electric Company:
(1) SEER = EER ÷ 0.9
(2) SEER = COP x 3.792
(3) EER = COP x 3.413
From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43 units of heat energy are pumped per unit of work energy.
Today, it is rare to see systems rated below SEER 9 in the United States, since older units are being replaced with higher-efficiency units. The United States now requires that residential systems manufactured in 2006 have a minimum SEER rating of 13 (although window-box systems are exempt from this law, so their SEER is still around 10). Substantial energy savings can be obtained from more efficient systems. For example by upgrading from SEER 9 to SEER 13, the power consumption is reduced by 30% (equal to 1 - 9/13). It is claimed that this can result in an energy savings valued at up to US$300 per year (depending on the usage rate and the cost of electricity). In many cases, the lifetime energy savings are likely to surpass the higher initial cost of a high-efficiency unit.
As an example, the annual cost of electric power consumed by a 72,000 BTU/h air conditioning unit operating for 1000 hours per year with a SEER rating of 10 and a power cost of $0.08 per kilowatt hour (kW·h) may be calculated as follows:
unit size, BTU/h × hours per year, h × power cost, $/kW·h ÷ (SEER, BTU/W·h × 1000 W/kW)
(72,000 BTU/h) × (1000 h) × ($0.08/kW·h) ÷ [(10 BTU/W·h) × (1000 W/kW)] = $576.00 annual cost
A common misconception is that the SEER rating system also applies to heating systems. However, SEER ratings only apply to air conditioning.
Air conditioners (for cooling) and heat pumps (for heating) both work similarly in that heat is transferred or "pumped" from a cooler heat source to a warmer "heat sink". Air conditioners and heat pumps usually operate most effectively at temperatures around 10 to 13 degrees Celsius (°C) (50 to 55 degrees Fahrenheit (°F)). A balance point is reached when the heat source temperature falls below about 4 °C (40 °F), and the system is not able to pull any more heat from the heat source (this point varies from heat pump to heat pump). Similarly, when the heat sink temperature rises to about 49 °C (120 °F), the system will operate less effectively, and will not be able to "push" out any more heat. Geothermal heat pumps do not have this problem of reaching a balance point because they use the ground as a heat source/heat sink and the ground's thermal inertia prevents it from becoming too cold or too warm when moving heat from or to it. The ground's temperature does not vary nearly as much over a year as that of the air above it.
Main article: Air conditioning#History
In 1820, British scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida. He hoped eventually to use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities. Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. His hopes for its success vanished soon afterward when his chief financial backer died; Gorrie did not get the money he needed to develop the machine. According to his biographer Vivian M. Sherlock, he blamed the "Ice King", Frederic Tudor, for his failure, suspecting that Tudor had launched a smear campaign against his invention. Dr. Gorrie died impoverished in 1855 and the idea of air conditioning faded away for 50 years.
Early commercial applications of air conditioning were manufactured to cool air for industrial processing rather than personal comfort. In 1902 the first modern electrical air conditioning was invented by Willis Haviland Carrier in Syracuse, NY. Designed to improve manufacturing process control in a printing plant, his invention controlled not only temperature but also humidity. The low heat and humidity were to help maintain consistent paper dimensions and ink alignment. Later Carrier's technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of America was formed to meet rising demand. Over time air conditioning came to be used to improve comfort in homes and automobiles. Residential sales expanded dramatically in the 1950s.
In 1906, Stuart W. Cramer of Charlotte, North Carolina, was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning", using it in a patent claim he filed that year as an analogue to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company. This evaporation of water in air, to provide a cooling effect, is now known as evaporative cooling.
The first air conditioners and refrigerators employed toxic or flammable gases like ammonia, methyl chloride, and propane which could result in fatal accidents when they leaked. Thomas Midgley, Jr. created the first chlorofluorocarbon gas, Freon, in 1928. The refrigerant was much safer for humans but was later found to be harmful to the atmosphere's ozone layer. Freon is a trademark name of DuPont for any Chlorofluorocarbon (CFC), Hydrogenated CFC (HCFC), or Hydrofluorocarbon (HFC) refrigerant, the name of each including a number indicating molecular composition (R-11, R-12, R-22, R-134A). The blend most used in direct-expansion home and building comfort cooling is an HCFC known as R-22. It is to be phased out for use in new equipment by 2010 and completely discontinued by 2020. R-12 was the most common blend used in automobiles in the US until 1994 when most changed to R-134A. R-11 and R-12 are no longer manufactured in the US, the only source for purchase being the cleaned and purified gas recovered from other air conditioner systems. Several non-ozone depleting refrigerants have been developed as alternatives, including R-410A, known by the brand name Puron.
Innovation in air conditioning technologies continue, with much recent emphasis placed on energy efficiency and improving indoor air quality. As an alternative to conventional refrigerants, natural alternatives like CO2 (R-744) have been proposed
Refrigeration cycle
A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor.
In the refrigeration cycle, a heat pump transfers heat from a lower-temperature heat source into a higher-temperature heat sink. Heat would naturally flow in the opposite direction. This is the most common type of air conditioning. A refrigerator works in much the same way, as it pumps the heat out of the interior into the room in which it stands.
This cycle takes advantage of the way phase changes work, where latent heat is released at a constant temperature during a liquid/gas phase change, and where varying the pressure of a pure substance also varies its condensation/boiling point.
The most common refrigeration cycle uses an electric motor to drive a compressor. In an automobile, the compressor is driven by a belt over a pulley, the belt being driven by the engine's crankshaft (similar to the driving of the pulleys for the alternator, power steering, etc.). Whether in a car or building, both use electric fan motors for air circulation. Since evaporation occurs when heat is absorbed, and condensation occurs when heat is released, air conditioners use a compressor to cause pressure changes between two compartments, and actively condense and pump a refrigerant around. A refrigerant is pumped into the cooled compartment (the evaporator coil), where the low pressure causes the refrigerant to evaporate into a vapor, taking heat with it. In the other compartment (the condenser), the refrigerant vapor is compressed and forced through another heat exchange coil, condensing into a liquid, rejecting the heat previously absorbed from the cooled space.
Humidity
Air conditioning equipment usually reduces the humidity of the air processed by the system. The relatively cold (below the dew point) evaporator coil condenses water vapor from the processed air, much like a cold drink will condense water on the outside of a glass. The water is drained, removing water vapor from the cooled space and thereby lowering its relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In food retail establishments, large, open chiller cabinets act as highly effective dehumidifiers.
Some air conditioning units dry the air without cooling it. These work like a normal air conditioner, except that a heat exchanger is placed between the intake and exhaust. In combination with convection fans, they achieve a similar level of comfort as an air cooler in humid tropical climates, but only consume about one-third the energy. They are also preferred by those who find the draft created by air coolers uncomfortable.
Refrigerants
Main article: Refrigerant
"Freon" is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties. Unfortunately, evidence has accumulated that these chlorine-bearing refrigerants reach the upper atmosphere when they escape. Once the refrigerant reaches the stratosphere, UV radiation from the Sun cleaves the chlorine-carbon bond, yielding a chlorine radical. These chlorine atoms catalyze the breakdown of ozone into diatomic oxygen, depleting the ozone layer that shields the Earth's surface from strong UV radiation. Each chlorine radical remains active as a catalyst unless it binds with another chlorine radical, forming a stable molecule and breaking the chain reaction. CFC refrigerants in common but decreasing usage include R-11 and R-12. Newer and more environmentally-safe refrigerants such as HCFCs (R-22, used in most homes today) and HFCs (R-134a, used in most cars) have replaced most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hydrofluorocarbons (HFCs) such as R-410A, which lack chlorine.
The external section of a typical single-room air conditioning unit. For ease of installation, these are frequently placed in a window. This one was installed through a hole cut in the wall.
The internal section of the above unit. The front panel swings down to reveal the controls.
Internal section of a modern Americool window air conditioner.
Types of air conditioner equipment
Window and through-wall units
Many traditional air conditioners in homes or other buildings are single rectangular units used to cool all or a portion of an apartment, house, or other building. Hotels frequently use PTAC systems, which combine heating and air conditioning into the same unit. Air conditioner units need to have access to the space they are cooling (the inside) and a heat sink; normally outside air is used to cool the condenser section. For this reason, single unit air conditioners are placed in windows or through openings in a wall made for the air conditioner; the latter type includes portable air conditioners.
Window and through-wall units have vents on both the inside and outside, so inside air to be cooled can be blown in and out by a fan in the unit, and outside air can also be blown in and out by another fan to act as the heat sink. The controls are on the inside.
A large house or building may have several such units. Should virtually every room be cooled with its own air conditioning unit, most of the day, it would be less expensive to use central air conditioning, though that may not be physically possible.
Evaporative coolers
Main article: Evaporative cooler
In very dry climates, evaporative coolers are popular for improving comfort during hot weather. This type of cooler is the dominant cooler used in Iran, which has the largest number of these units of any country in the world, causing some to referring to these units as "Persian coolers."[4] An evaporative cooler is a device that draws outside air through a wet pad, such as a large sponge soaked with water. The sensible heat of the incoming air, as measured by a dry bulb thermometer, is reduced. The total heat (sensible heat plus latent heat) of the entering air is unchanged. Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite comfortable. These coolers cost less and are mechanically simple to understand and maintain.
An early type of cooler, using ice for a further effect, was patented by John Gorrie of Apalachicola, Florida in 1842. He used the device to cool the patients in his malaria hospital.
Absorptive chillers
Main article: Absorption refrigerator
Central air conditioning
Central air conditioning, commonly referred to as central air (U.S.) or air-con (UK), is an air conditioning system which uses ducts to distribute cooled and/or dehumidified air to more than one room, or uses pipes to distribute chilled water to heat exchangers in more than one room, and which is not plugged into a standard electrical outlet.
With a typical split system, the condenser and compressor are located in an outdoor unit; the evaporator is mounted in the air handler unit. With a package system, all components are located in a single outdoor unit that may be located on the ground or roof.
Central air conditioning performs like a regular air conditioner but has several added benefits:
When the air handling unit turns on, room air is drawn in from various parts of the building through return-air ducts. This air is pulled through a filter where airborne particles such as dust and lint are removed. Sophisticated filters may remove microscopic pollutants as well. The filtered air is routed to air supply ductwork that carries it back to rooms. Whenever the air conditioner is running, this cycle repeats continually.
Because the central air conditioning unit is located outside the home, it offers a lower level of indoor noise than a free-standing air conditioning unit.
Thermostats
Main article: Thermostat
Thermostats control the operation of HVAC systems, turning on the heating or cooling systems to bring the building to the set temperature. Typically the heating and cooling systems have separate control systems (even though they may share a thermostat) so that the temperature is only controlled "one-way." That is, in cold weather, a building that is too hot will not be cooled by the thermostat. Thermostats may also be incorporated into facility energy management systems in which the power utility customer may control the overall energy expenditure. In addition, a growing number of power utilities have made available a device which, when professionally installed, will control or limit the power to an HVAC system during peak use times in order to avoid necessitating the use of rolling blackouts. The customer is given a credit of some sort in exchange, so it is often to the advantage of the consumer to buy the most efficient thermostat possible.
Equipment capacity
Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration." A "ton of refrigeration" is defined as the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. This is equal to 12,000 BTU per hour, or 3517 watts.Residential central air systems are usually from 1 to 5 tons (3 to 20 kilowatts (kW)) in capacity.
The use of electric/compressive air conditioning puts a major demand on the electrical power grid in warm weather, when most units are operating under heavy load. In the aftermath of the 2003 North America blackout locals were asked to keep their air conditioning off. During peak demand, additional power plants must often be brought online, usually expensive peaker plants. A 1995 meta-analysis of various utility studies concluded that the average air conditioner wasted 40% of the input energy. This energy is lost in the form of heat, which must be pumped out. There is a huge opportunity to reduce the need for new power plants and to conserve energy.
In an automobile, the A/C system will use around 5 horsepower (4 kW) of the engine's power.
Seasonal Energy Efficiency Rating (SEER)
Main article: Seasonal Energy Efficiency Rating
For residential homes, some countries set minimum requirements for energy efficiency. In the United States, the efficiency of air conditioners is often (but not always) rated by the Seasonal Energy Efficiency Ratio (SEER). The higher the SEER rating, the more energy efficient is the air conditioner. The SEER rating is the BTU of cooling output during its normal annual usage divided by the total electric energy input in watt hours (W·h) during the same period.
SEER = BTU ÷ W·h
For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, operating for a total of 1000 hours during an annual cooling season (i.e., 8 hours per day for 125 days) would provide an annual total cooling output of:
5000 BTU/h × 1000 h = 5,000,000 BTU
which, for a SEER of 10, would be an annual electrical energy usage of:
5,000,000 BTU ÷ 10 = 500,000 W·h
and that is equivalent to an average power usage during the cooling season of:
500,000 W·h ÷ 1000 h = 500 W
SEER is related to the coefficient of performance (COP) commonly used in thermodynamics and also to the Energy Efficiency Ratio (EER). The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures, while SEER is calculated over a whole range of external temperatures (i.e., the temperature distribution for the geographical location of the SEER test). SEER is unusual in that it is composed of an Imperial unit divided by an SI unit. The COP is a ratio with the same metric units of energy (joules) in both the numerator and denominator. They cancel out, leaving a dimensionless quantity. Formulas for the approximate conversion between SEER and EER or COP are available from the Pacific Gas and Electric Company:
(1) SEER = EER ÷ 0.9
(2) SEER = COP x 3.792
(3) EER = COP x 3.413
From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43 units of heat energy are pumped per unit of work energy.
Today, it is rare to see systems rated below SEER 9 in the United States, since older units are being replaced with higher-efficiency units. The United States now requires that residential systems manufactured in 2006 have a minimum SEER rating of 13 (although window-box systems are exempt from this law, so their SEER is still around 10). Substantial energy savings can be obtained from more efficient systems. For example by upgrading from SEER 9 to SEER 13, the power consumption is reduced by 30% (equal to 1 - 9/13). It is claimed that this can result in an energy savings valued at up to US$300 per year (depending on the usage rate and the cost of electricity). In many cases, the lifetime energy savings are likely to surpass the higher initial cost of a high-efficiency unit.
As an example, the annual cost of electric power consumed by a 72,000 BTU/h air conditioning unit operating for 1000 hours per year with a SEER rating of 10 and a power cost of $0.08 per kilowatt hour (kW·h) may be calculated as follows:
unit size, BTU/h × hours per year, h × power cost, $/kW·h ÷ (SEER, BTU/W·h × 1000 W/kW)
(72,000 BTU/h) × (1000 h) × ($0.08/kW·h) ÷ [(10 BTU/W·h) × (1000 W/kW)] = $576.00 annual cost
A common misconception is that the SEER rating system also applies to heating systems. However, SEER ratings only apply to air conditioning.
Air conditioners (for cooling) and heat pumps (for heating) both work similarly in that heat is transferred or "pumped" from a cooler heat source to a warmer "heat sink". Air conditioners and heat pumps usually operate most effectively at temperatures around 10 to 13 degrees Celsius (°C) (50 to 55 degrees Fahrenheit (°F)). A balance point is reached when the heat source temperature falls below about 4 °C (40 °F), and the system is not able to pull any more heat from the heat source (this point varies from heat pump to heat pump). Similarly, when the heat sink temperature rises to about 49 °C (120 °F), the system will operate less effectively, and will not be able to "push" out any more heat. Geothermal heat pumps do not have this problem of reaching a balance point because they use the ground as a heat source/heat sink and the ground's thermal inertia prevents it from becoming too cold or too warm when moving heat from or to it. The ground's temperature does not vary nearly as much over a year as that of the air above it.
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