工业制冷论文文献

制冷 RefrigerationRefrigeration is the process of removing heat from an enclosed space, or from a substance, and rejecting it elsewhere for the primary purpose of lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. The term cooling refers generally to any natural or artificial process by which heat is dissipated. The process of artificially producing extreme cold temperatures is referred to as cryogenics.Cold is the absence of heat, hence in order to decrease a temperature, one "removes heat", rather than "adding cold." In order to satisfy the Second Law of Thermodynamics, some form of work must be performed to accomplish this. This work is traditionally done by mechanical work but can also be done by magnetism, laser or other means. However, all refrigeration uses the three basic methods of heat transfer: convection, conduction, or radiation.Historical applicationsIce harvestingThe use of ice to refrigerate and thus preserve food goes back to prehistoric times.Through the ages, the seasonal harvesting of snow and ice was a regular practice of most of the ancient cultures: Chinese, Hebrews, Greeks, Romans, Persians. Ice and snow were stored in caves or dugouts lined with straw or other insulating materials. The Persians stored ice in pits called yahairas. Rationing of the ice allowed the preservation of foods over the cold periods. This practice worked well down through the centuries, with icehouses remaining in use into the twentieth century.In the 16th century, the discovery of chemical refrigeration was one of the first steps toward artificial means of refrigeration. Sodium nitrate or potassium nitrate, when added to water, lowered the water temperature and created a sort of refrigeration bath for cooling substances. In Italy, such a solution was used to chill wine.During the first half of the 19th century, ice harvesting became big business in America. New Englander Frederic Tudor, who became known as the "Ice King", worked on developing better insulation products for the long distance shipment of ice, especially to the tropics.First refrigeration systemsThe first known method of artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in 1748. Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled , absorbing heat from the surrounding air. The experiment even created a small amount of ice, but had no practical application at that time.In 1805, American inventor Oliver Evans designed but never built a refrigeration system based on the vapor-compression refrigeration cycle rather than chemical solutions or volatile liquids such as ethyl ether.In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low temperatures.An American living in Great Britain, Jacob Perkins, obtained the first patent for a vapor-compression refrigeration system in 1834. Perkins built a prototype system and it actually worked, although it did not succeed commercially.In 1842, an American physician, John Gorrie, designed the first system for refrigerating water to produce ice. He also conceived the idea of using his refrigeration system to cool the air for comfort in homes and hospitals (i.e., air-conditioning). His system compressed air, then partially cooled the hot compressed air with water before allowing it to expand while doing part of the work required to drive the air compressor. That isentropic expansion cooled the air to a temperature low enough to freeze water and produce ice, or to flow "through a pipe for effecting refrigeration otherwise" as stated in his patent granted by the U.S. Patent Office in 1851. Gorrie built a working prototype, but his system was a commercial failure.Alexander Twining began experimenting with vapor-compression refrigeration in 1848 and obtained patents in 1850 and 1853. He is credited with having initiated commercial refrigeration in the United States by 1856.Meanwhile, James Harrison who was born in Scotland and subsequently emigrated to Australia, begun operation of a mechanical ice-making machine in 1851 on the banks of the Barwon River at Rocky Point in Geelong. His first commercial ice-making machine followed in 1854 and his patent for an ether liquid-vapour compression refrigeration system was granted in 1855. Harrison introduced commercial vapor-compression refrigeration to breweries and meat packing houses and by 1861, a dozen of his systems were in operation.Australian, Argentinean and American concerns experimented with refrigerated shipping in the mid 1870s, the first commercial success coming when William Soltau Davidson fitted a compression refrigeration unit to the New Zealand vessel Dunedin in 1882, leading to a meat and dairy boom in Australasia and South America.The first gas absorption refrigeration system using gaseous ammonia dissolved in water (referred to as "aqua ammonia") was developed by Ferdinand Carré of France in 1859 and patented in 1860. Due to the toxicity of ammonia, such systems were not developed for use in homes, but were used to manufacture ice for sale. In the United States, the consumer public at that time still used the ice box with ice brought in from commercial suppliers, many of whom were still harvesting ice and storing it in an icehouse.Thaddeus Lowe, an American balloonist from the Civil War, had experimented over the years with the properties of gases. One of his mainstay enterprises was the high-volume production of hydrogen gas. He also held several patents on ice making machines. His "Compression Ice Machine" would revolutionize the cold storage industry. In 1869 he and other investors purchased an old steamship onto which they loaded one of Lowe’s refrigeration units and began shipping fresh fruit from New York to the Gulf Coast area, and fresh meat from Galveston, Texas back to New York. Because of Lowe’s lack of knowledge about shipping, the business was a costly failure, and it was difficult for the public to get used to the idea of being able to consume meat that had been so long out of the packing house.Domestic mechanical refrigerators became available in the United States around 1911.Widespread commercial useBy the 1870s breweries had become the largest users of commercial refrigeration units, though some still relied on harvested ice. Though the ice-harvesting industry had grown immensely by the turn of the 20th century, pollution and sewage had begun to creep into natural ice making it a problem in the metropolitan suburbs. Eventually breweries began to complain of tainted ice. This raised demand for more modern and consumer-ready refrigeration and ice-making machines. In 1895 German engineer Carl von Linde set up a large-scale process for the production of liquid air and eventually liquid oxygen for use in safe household refrigerators.Refrigerated railroad cars were introduced in the US in the 1840s for the short-run transportation of dairy products. In 1867 J.B. Sutherland of Detroit, Michigan patented the refrigerator car designed with ice tanks at either end of the car and ventilator flaps near the floor which would create a gravity draft of cold air through the car.By 1900 the meat packing houses of Chicago had adopted ammonia-cycle commercial refrigeration. By 1914 almost every location used artificial refrigeration. The big meat packers, Armour, Swift, and Wilson, had purchased the most expensive units which they installed on train cars and in branch houses and storage facilities in the more remote distribution areas.It was not until the middle of the 20th century that refrigeration units were designed for installation on tractor-trailer rigs (trucks or lorries). Refrigerated vehicles are used to transport perishable goods, such as frozen foods, fruit and vegetables, and temperature-sensitive chemicals. Most modern refrigerators keep the temperature between -40 and +20 °C and have a maximum payload of around 24 000 kg. gross weight (in Europe).Home and consumer useWith the invention of synthetic refrigerations based mostly on a chlorofluorocarbon (CFC) chemical, safer refrigerators were possible for home and consumer use. Freon is a trademark of the Dupont Corporation and refers to these CFC, and later hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC), refrigerants.Developed in the late 1920's, these refrigerants were considered at the time to be less harmful than the commonly used refrigerants of the time, including methyl formate, ammonia, methyl chloride, and sulfur dioxide. The intent was to provide refrigeration equipment for home use without endangering the lives of the occupants. These CFC refrigerants answered that need.The Montreal ProtocolAs of 1989, CFC-based refrigerant was banned via the Montreal Protocol due to the negative effects it has on the ozone layer. The Montreal Protocol was ratified by most CFC producing and consuming nations in Montreal, Quebec, Canada in September 1987. Greenpeace objected to the ratification because the Montreal Protocol instead ratified the use of HFC refrigeration, which are not ozone depleting but are still powerful global warming gases. Searching for an alternative for home use refrigeration, dkk Scharfenstein (Germany) developed a propane-based CFC as well as an HFC-free refrigerator in 1992 with assistance from Greenpeace.[citation needed]The tenets of the Montreal Protocol were put into effect in the United States via the Clean Air Act legislation in August 1988. The Clean Air Act was further amended in 1990. This was a direct result of a scientific report released in June 1974 by Rowland-Molina, detailing how chlorine in CFC and HCFC refrigerants adversely affected the ozone layer. This report prompted the FDA and EPA to ban CFCs as a propellant in 1978 (50% of CFC use at that time was for aerosol can propellant).In January 1992, the EPA required that refrigerant be recovered from all automotive air conditioning systems during system service. In July 1992, the EPA made illegal the venting of CFC and HCFC refrigerants. In June 1993, the EPA required that major leaks in refrigeration systems be fixed within 30 days. A major leak was defined as a leak rate that would equal 35% of the total refrigerant charge of the system (for industrial and commercial refrigerant systems), or 15% of the total refrigerant charge of the system (for all other large refrigerant systems), if that leak were to proceed for an entire year. In July 1993, the EPA instituted the Safe Disposal Requirements, requiring that all refrigerant systems be evacuated prior to retirement or disposal (no matter the size of the system), and putting the onus on the last person in the disposal chain to ensure that the refrigerant was properly captured. In August 1993, the EPA implemented reclamation requirements for refrigerant. If a refrigerant is to change ownership, it must be processed and tested to comply with the American Refrigeration Institute (ARI) standard 700-1993 (now ARI standard 700-1995) requirements for refrigerant purity. In November 1993, the EPA required that all refrigerant recovery equipment meet the standards of ARI 740-1993. In November 1995, the EPA also restricted the venting of HFC refrigerants. These contain no chlorine that can damage the ozone layer (and thus have an ODP (Ozone Depletion Potential) of zero), but still have a high global warming potential. In December 1995, CFC refrigerant importation and production in the US was banned. It is currently planned to ban all HCFC refrigerant importation and production in the year 2030, although that will likely be accelerated.Current applications of refrigerationProbably the most widely-used current applications of refrigeration are for the air-conditioning of private homes and public buildings, and the refrigeration of foodstuffs in homes, restaurants and large storage warehouses. The use of refrigerators in our kitchens for the storage of fruits and vegetables has allowed us to add fresh salads to our diets year round, and to store fish and meats safely for long periods.In commerce and manufacturing, there are many uses for refrigeration. Refrigeration is used to liquify gases like oxygen, nitrogen, propane and methane for example. In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture content. In oil refineries, chemical plants, and petrochemical plants, refrigeration is used to maintain certain processes at their required low temperatures (for example, in the alkylation of butenes and butane to produce a high octane gasoline component). Metal workers use refrigeration to temper steel and cutlery. In transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes and sea-going vessels, refrigeration is a necessity.Dairy products are constantly in need of refrigeration, and it was only discovered in the past few decades that eggs needed to be refrigerated during shipment rather than waiting to be refrigerated after arrival at the grocery store. Meats, poultry and fish all must be kept in climate-controlled environments before being sold. Refrigeration also helps keep fruits and vegetables edible longer.One of the most influential uses of refrigeration was in the development of the sushi/sashimi industry in Japan. Prior to the discovery of refrigeration, many sushi connoisseurs suffered great morbidity and mortality from diseases such as hepatitis A[citation needed], and Diphyllobothriosis, from a common oceanic tapeworm - Diphyllobothrium latum Oiler99 (talk) 19:09, 26 May 2008 (UTC) . However the dangers of unrefrigerated sashimi was not brought to light for decades due to the lack of research and healthcare distribution across rural Japan. Around mid-century, the Zojirushi corporation based in Kyoto made breakthroughs in refrigerator designs making refrigerators cheaper and more accessible for restaurant proprietors and the general public.Methods of refrigerationMethods of refrigeration can be classified as non-cyclic, cyclic and thermoelectric.Non-cyclic refrigerationIn these methods, refrigeration can be accomplished by melting ice or by subliming dry ice. These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable coolers.Ice owes its effectiveness as a cooling agent to its constant melting point of 0 °C (32 °F). In order to melt, ice must absorb 333.55 kJ/kg (approx. 144 Btu/lb) of heat. Foodstuffs maintained at this temperature or slightly above have an increased storage life. Solid carbon dioxide, known as dry ice, is used also as a refrigerant. Having no liquid phase at normal atmospheric pressure, it sublimes directly from the solid to vapor phase at a temperature of -78.5 °C (-109.3 °F). Dry ice is effective for maintaining products at low temperatures during the period of sublimation.Cyclic refrigerationMain article: Heat pump and refrigeration cycleThis consists of a refrigeration cycle, where heat is removed from a low-temperature space or source and rejected to a high-temperature sink with the help of external work, and its inverse, the thermodynamic power cycle. In the power cycle, heat is supplied from a high-temperature source to the engine, part of the heat being used to produce work and the rest being rejected to a low-temperature sink. This satisfies the second law of thermodynamics.A refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and rejects heat as it circulates through a refrigerator. It is also applied to HVACR work, when describing the "process" of refrigerant flow through an HVACR unit, whether it is a packaged or split system.Heat naturally flows from hot to cold. Work is applied to cool a living space or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink. Insulation is used to reduce the work and energy required to achieve and maintain a lower temperature in the cooled space. The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in 1824 as a heat engine.The most common types of refrigeration systems use the reverse-Rankine vapor-compression refrigeration cycle although absorption heat pumps are used in a minority of applications.Cyclic refrigeration can be classified as:Vapor cycle, and Gas cycle Vapor cycle refrigeration can further be classified as:Vapor compression refrigeration Vapor absorption refrigeration

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