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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 The term cooling refers generally to any natural or artificial process by which heat is The process of artificially producing extreme cold temperatures is referred to as Cold is the absence of heat, hence in order to decrease a temperature, one "removes heat", rather than "adding " In order to satisfy the Second Law of Thermodynamics, some form of work must be performed to accomplish This work is traditionally done by mechanical work but can also be done by magnetism, laser or other However, all refrigeration uses the three basic methods of heat transfer: convection, conduction, or Historical applicationsIce harvestingThe use of ice to refrigerate and thus preserve food goes back to prehistoric Through the ages, the seasonal harvesting of snow and ice was a regular practice of most of the ancient cultures: Chinese, Hebrews, Greeks, Romans, P Ice and snow were stored in caves or dugouts lined with straw or other insulating The Persians stored ice in pits called Rationing of the ice allowed the preservation of foods over the cold This practice worked well down through the centuries, with icehouses remaining in use into the twentieth In the 16th century, the discovery of chemical refrigeration was one of the first steps toward artificial means of Sodium nitrate or potassium nitrate, when added to water, lowered the water temperature and created a sort of refrigeration bath for cooling In Italy, such a solution was used to chill During the first half of the 19th century, ice harvesting became big business in A 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 First refrigeration systemsThe first known method of artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled , absorbing heat from the surrounding The experiment even created a small amount of ice, but had no practical application at that 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 In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low An American living in Great Britain, Jacob Perkins, obtained the first patent for a vapor-compression refrigeration system in Perkins built a prototype system and it actually worked, although it did not succeed In 1842, an American physician, John Gorrie, designed the first system for refrigerating water to produce He also conceived the idea of using his refrigeration system to cool the air for comfort in homes and hospitals (, 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 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 US Patent Office in Gorrie built a working prototype, but his system was a commercial Alexander Twining began experimenting with vapor-compression refrigeration in 1848 and obtained patents in 1850 and He is credited with having initiated commercial refrigeration in the United States by 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 G His first commercial ice-making machine followed in 1854 and his patent for an ether liquid-vapour compression refrigeration system was granted in Harrison introduced commercial vapor-compression refrigeration to breweries and meat packing houses and by 1861, a dozen of his systems were in 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 AThe 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 Due to the toxicity of ammonia, such systems were not developed for use in homes, but were used to manufacture ice for 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 Thaddeus Lowe, an American balloonist from the Civil War, had experimented over the years with the properties of One of his mainstay enterprises was the high-volume production of hydrogen He also held several patents on ice making His "Compression Ice Machine" would revolutionize the cold storage 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 Y 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 Domestic mechanical refrigerators became available in the United States around Widespread commercial useBy the 1870s breweries had become the largest users of commercial refrigeration units, though some still relied on harvested 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 Eventually breweries began to complain of tainted This raised demand for more modern and consumer-ready refrigeration and ice-making 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 Refrigerated railroad cars were introduced in the US in the 1840s for the short-run transportation of dairy In 1867 JB 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 By 1900 the meat packing houses of Chicago had adopted ammonia-cycle commercial By 1914 almost every location used artificial 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 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 Most modern refrigerators keep the temperature between -40 and +20 °C and have a maximum payload of around 24 000 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 Freon is a trademark of the Dupont Corporation and refers to these CFC, and later hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC), 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 The intent was to provide refrigeration equipment for home use without endangering the lives of the These CFC refrigerants answered that The Montreal ProtocolAs of 1989, CFC-based refrigerant was banned via the Montreal Protocol due to the negative effects it has on the ozone The Montreal Protocol was ratified by most CFC producing and consuming nations in Montreal, Quebec, Canada in September 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 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 G[citation needed]The tenets of the Montreal Protocol were put into effect in the United States via the Clean Air Act legislation in August The Clean Air Act was further amended in 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 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 In July 1992, the EPA made illegal the venting of CFC and HCFC In June 1993, the EPA required that major leaks in refrigeration systems be fixed within 30 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 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 In August 1993, the EPA implemented reclamation requirements for 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 In November 1993, the EPA required that all refrigerant recovery equipment meet the standards of ARI 740- In November 1995, the EPA also restricted the venting of HFC 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 In December 1995, CFC refrigerant importation and production in the US was It is currently planned to ban all HCFC refrigerant importation and production in the year 2030, although that will likely be 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 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 In commerce and manufacturing, there are many uses for Refrigeration is used to liquify gases like oxygen, nitrogen, propane and methane for In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture 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 In transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes and sea-going vessels, refrigeration is a 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 Meats, poultry and fish all must be kept in climate-controlled environments before being Refrigeration also helps keep fruits and vegetables edible One of the most influential uses of refrigeration was in the development of the sushi/sashimi industry in J 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 J 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 Methods of refrigerationMethods of refrigeration can be classified as non-cyclic, cyclic and Non-cyclic refrigerationIn these methods, refrigeration can be accomplished by melting ice or by subliming dry These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable 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 55 kJ/kg ( 144 Btu/lb) of Foodstuffs maintained at this temperature or slightly above have an increased storage Solid carbon dioxide, known as dry ice, is used also as a Having no liquid phase at normal atmospheric pressure, it sublimes directly from the solid to vapor phase at a temperature of -5 °C (-3 °F) Dry ice is effective for maintaining products at low temperatures during the period of 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 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 This satisfies the second law of A refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and rejects heat as it circulates through a 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 Heat naturally flows from hot to 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 Insulation is used to reduce the work and energy required to achieve and maintain a lower temperature in the cooled The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in 1824 as a heat 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 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
If the entering air condition ischanged to Point D at the same wet-bulb temperature but at a higherdry-bulb temperature, the total heat transfer (Vector DB) remainsthe same, but the sensible and latent components change dramati- DE represents sensible cooling of air, while EB representslatent heating as water gives up heat and mass to the Thus, forthe same water-cooling load, the ratio of latent to sensible heattransfer can vary The ratio of latent to sensible heat is important in analyzing waterusage of a cooling Mass transfer (evaporation) occurs only inthe latent portion of heat transfer and is proportional to the changein specific Because the entering air dry-bulb temperatureor relative humidity affects the latent to sensible heat transfer ratio,it also affects the rate of In Figure 2, the rate of evapo-ration in Case AB (WB − WA) is less than in Case DB (WB − WD)because the latent heat transfer (mass transfer) represents a smallerportion of the The evaporation rate at typical design conditions is approximately1% of the water flow rate for each 7 K of water temperature range;however, the average evaporation rate over the operating season isless than the design rate because the sensible component of total heattransfer increases as entering air temperature In addition to water loss from evaporation, losses also occurbecause of liquid carryover into the discharge airstream and blow-down to maintain acceptable water 如果是进入空调改为D点在同一湿球温度，但在较高干球温度，总传热（矢量数据库）仍然相同，但明智的和潜在的组成部分的剧作家，卡利。明智署署长代表空气冷却，而电子束代表潜热，水热，放弃了对空气质量。因此，同样的水冷却负荷，潜显热比转移有很大的差别。对潜在的比例显热分析是很重要的水使用的冷却塔。传质（蒸发）只发生在潜在的传热部分，是成比例的改变在具体的湿度。由于进入空气干球温度或相对湿度影响潜到显热传递率，它也影响到蒸发率。在图2中，土壤水分蒸发的速度，在个案公司（世行 - WA）的比例是比案例数据库（世行 - 西数较少）因为潜热转移（质）代表一个较小的部分总额。在典型的设计条件下蒸发率约为1％的水每7 K表温度范围内水流量;但是，在工作赛季平均蒸发量低于设计速度，因为总热量合理成分作为进入空气温度降低转移增加。除了水的蒸发损失，损失也可能发生由于结转到液体排放气流吹到保持可接受的水质。
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 The term cooling refers generally to any natural or artificial process by which heat is The process of artificially producing extreme cold temperatures is referred to as Cold is the absence of heat, hence in order to decrease a temperature, one "removes heat", rather than "adding " In order to satisfy the Second Law of Thermodynamics, some form of work must be performed to accomplish This work is traditionally done by mechanical work but can also be done by magnetism, laser or other However, all refrigeration uses the three basic methods of heat transfer: convection, conduction, or Historical applicationsIce harvestingThe use of ice to refrigerate and thus preserve food goes back to prehistoric Through the ages, the seasonal harvesting of snow and ice was a regular practice of most of the ancient cultures: Chinese, Hebrews, Greeks, Romans, P Ice and snow were stored in caves or dugouts lined with straw or other insulating The Persians stored ice in pits called Rationing of the ice allowed the preservation of foods over the cold This practice worked well down through the centuries, with icehouses remaining in use into the twentieth In the 16th century, the discovery of chemical refrigeration was one of the first steps toward artificial means of Sodium nitrate or potassium nitrate, when added to water, lowered the water temperature and created a sort of refrigeration bath for cooling In Italy, such a solution was used to chill During the first half of the 19th century, ice harvesting became big business in A 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 First refrigeration systemsThe first known method of artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled , absorbing heat from the surrounding The experiment even created a small amount of ice, but had no practical application at that 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 In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low An American living in Great Britain, Jacob Perkins, obtained the first patent for a vapor-compression refrigeration system in Perkins built a prototype system and it actually worked, although it did not succeed In 1842, an American physician, John Gorrie, designed the first system for refrigerating water to produce He also conceived the idea of using his refrigeration system to cool the air for comfort in homes and hospitals (, 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 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 US Patent Office in Gorrie built a working prototype, but his system was a commercial Alexander Twining began experimenting with vapor-compression refrigeration in 1848 and obtained patents in 1850 and He is credited with having initiated commercial refrigeration in the United States by 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 G His first commercial ice-making machine followed in 1854 and his patent for an ether liquid-vapour compression refrigeration system was granted in Harrison introduced commercial vapor-compression refrigeration to breweries and meat packing houses and by 1861, a dozen of his systems were in 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 AThe 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 Due to the toxicity of ammonia, such systems were not developed for use in homes, but were used to manufacture ice for 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 Thaddeus Lowe, an American balloonist from the Civil War, had experimented over the years with the properties of One of his mainstay enterprises was the high-volume production of hydrogen He also held several patents on ice making His "Compression Ice Machine" would revolutionize the cold storage 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 Y 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 Domestic mechanical refrigerators became available in the United States around Widespread commercial useBy the 1870s breweries had become the largest users of commercial refrigeration units, though some still relied on harvested 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 Eventually breweries began to complain of tainted This raised demand for more modern and consumer-ready refrigeration and ice-making 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 Refrigerated railroad cars were introduced in the US in the 1840s for the short-run transportation of dairy In 1867 JB 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 By 1900 the meat packing houses of Chicago had adopted ammonia-cycle commercial By 1914 almost every location used artificial 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 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 Most modern refrigerators keep the temperature between -40 and +20 °C and have a maximum payload of around 24 000 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 Freon is a trademark of the Dupont Corporation and refers to these CFC, and later hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC), 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 The intent was to provide refrigeration equipment for home use without endangering the lives of the These CFC refrigerants answered that The Montreal ProtocolAs of 1989, CFC-based refrigerant was banned via the Montreal Protocol due to the negative effects it has on the ozone The Montreal Protocol was ratified by most CFC producing and consuming nations in Montreal, Quebec, Canada in September 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 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 G[citation needed]The tenets of the Montreal Protocol were put into effect in the United States via the Clean Air Act legislation in August The Clean Air Act was further amended in 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 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 In July 1992, the EPA made illegal the venting of CFC and HCFC In June 1993, the EPA required that major leaks in refrigeration systems be fixed within 30 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 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 In August 1993, the EPA implemented reclamation requirements for 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 In November 1993, the EPA required that all refrigerant recovery equipment meet the standards of ARI 740- In November 1995, the EPA also restricted the venting of HFC 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 In December 1995, CFC refrigerant importation and production in the US was It is currently planned to ban all HCFC refrigerant importation and production in the year 2030, although that will likely be 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 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 In commerce and manufacturing, there are many uses for Refrigeration is used to liquify gases like oxygen, nitrogen, propane and methane for In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture 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 In transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes and sea-going vessels, refrigeration is a 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 Meats, poultry and fish all must be kept in climate-controlled environments before being Refrigeration also helps keep fruits and vegetables edible One of the most influential uses of refrigeration was in the development of the sushi/sashimi industry in J 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 J 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 Methods of refrigerationMethods of refrigeration can be classified as non-cyclic, cyclic and Non-cyclic refrigerationIn these methods, refrigeration can be accomplished by melting ice or by subliming dry These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable 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 55 kJ/kg ( 144 Btu/lb) of Foodstuffs maintained at this temperature or slightly above have an increased storage Solid carbon dioxide, known as dry ice, is used also as a Having no liquid phase at normal atmospheric pressure, it sublimes directly from the solid to vapor phase at a temperature of -5 °C (-3 °F) Dry ice is effective for maintaining products at low temperatures during the period of 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 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 This satisfies the second law of A refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and rejects heat as it circulates through a 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 Heat naturally flows from hot to 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 Insulation is used to reduce the work and energy required to achieve and maintain a lower temperature in the cooled The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in 1824 as a heat 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 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
If the entering air condition ischanged to Point D at the same wet-bulb temperature but at a higherdry-bulb temperature, the total heat transfer (Vector DB) remainsthe same, but the sensible and latent components change dramati- DE represents sensible cooling of air, while EB representslatent heating as water gives up heat and mass to the Thus, forthe same water-cooling load, the ratio of latent to sensible heattransfer can vary The ratio of latent to sensible heat is important in analyzing waterusage of a cooling Mass transfer (evaporation) occurs only inthe latent portion of heat transfer and is proportional to the changein specific Because the entering air dry-bulb temperatureor relative humidity affects the latent to sensible heat transfer ratio,it also affects the rate of In Figure 2, the rate of evapo-ration in Case AB (WB − WA) is less than in Case DB (WB − WD)because the latent heat transfer (mass transfer) represents a smallerportion of the The evaporation rate at typical design conditions is approximately1% of the water flow rate for each 7 K of water temperature range;however, the average evaporation rate over the operating season isless than the design rate because the sensible component of total heattransfer increases as entering air temperature In addition to water loss from evaporation, losses also occurbecause of liquid carryover into the discharge airstream and blow-down to maintain acceptable water 如果是进入空调改为D点在同一湿球温度，但在较高干球温度，总传热（矢量数据库）仍然相同，但明智的和潜在的组成部分的剧作家，卡利。明智署署长代表空气冷却，而电子束代表潜热，水热，放弃了对空气质量。因此，同样的水冷却负荷，潜显热比转移有很大的差别。对潜在的比例显热分析是很重要的水使用的冷却塔。传质（蒸发）只发生在潜在的传热部分，是成比例的改变在具体的湿度。由于进入空气干球温度或相对湿度影响潜到显热传递率，它也影响到蒸发率。在图2中，土壤水分蒸发的速度，在个案公司（世行 - WA）的比例是比案例数据库（世行 - 西数较少）因为潜热转移（质）代表一个较小的部分总额。在典型的设计条件下蒸发率约为1％的水每7 K表温度范围内水流量;但是，在工作赛季平均蒸发量低于设计速度，因为总热量合理成分作为进入空气温度降低转移增加。除了水的蒸发损失，损失也可能发生由于结转到液体排放气流吹到保持可接受的水质。
testing of an air-cycle refrigeration system for road transportAbstractThe environmental attractions of air-cycle refrigeration are Following a thermodynamic design analysis, an air-cycle demonstrator plant was constructed within the restricted physical envelope of an existing Thermo King SL200 trailer refrigeration This unique plant operated satisfactorily, delivering sustainable cooling for refrigerated trailers using a completely natural and safe working The full load capacity of the air-cycle unit at −20 °C was 7,8 kW, 8% greater than the equivalent vapour-cycle unit, but the fuel consumption of the air-cycle plant was excessively However, at part load operation the disparity in fuel consumption dropped from approximately 200% to around 80% The components used in the air-cycle demonstrator were not optimised and considerable potential exists for efficiency improvements, possibly to the point where the air-cycle system could rival the efficiency of the standard vapour-cycle system at part-load operation, which represents the biggest proportion of operating time for most Keywords: Air conditioner; Refrigerated transport; Thermodynamic cycle; Air; Centrifuge compressor; Turbine expander COP, NomenclaturePRCompressor or turbine pressure ratioTAHeat exchanger side A temperature (K)TBHeat exchanger side B temperature (K)TinletInlet temperature (K)ToutletOutlet temperature (K)ηcompCompressor isentropic efficiencyηturbTurbine isentropic efficiencyηheat exchangerHeat exchanger IntroductionThe current legislative pressure on conventional refrigerants is well The reason why vapour-cycle refrigeration is preferred over air-cycle refrigeration is simply that in the great majority of cases vapour-cycle is the most energy efficient Consequently, as soon as alternative systems, such as non-HFC refrigerants or air-cycle systems are considered, the issue of increased energy consumption arises Concerns over legislation affecting HFC refrigerants and the desire to improve long-term system reliability led to the examination of the feasibility of an air-cycle system for refrigerated With the support of Enterprise Ireland and Thermo King (Ireland), the authors undertook the design and construction of an air-cycle refrigeration demonstrator plant at LYIT and QUB This was not the first time in recent years that air-cycle systems had been employed in NormalAir Garrett developed and commercialised an air-cycle air conditioning pack that was fitted to high speed trains in Germany in the As part of an European funded programme, a range of applications for air-cycle refrigeration were investigated and several demonstrator plants were However, the authors are unaware of any other case where a self-contained air-cycle unit has been developed for the challenging application of trailer Thermo King decided that the demonstrator should be a trailer refrigeration unit, since those were the units with the largest refrigeration capacity but presented the greatest challenges with regard to physical Consequently, the main objective was to demonstrate that an air-cycle system could fit within the existing physical envelop and develop an equivalent level of cooling power to the existing vapour-cycle unit, but using only air as the working The salient performance specifications for the existing Thermo King SL200 vapour-cycle trailer refrigeration unit are listed It was not the objective of the exercise to complete the design and development of a new refrigeration product that would be ready for To limit the level of resources necessary, existing hardware was to be used where possible with the recognition that the efficiencies achieved would not be In practical terms, this meant using the chassis and panels for an existing SL200 unit along with the standard diesel engine and circulation The turbomachinery used for compression and expansion was adapted from commercial Thermodynamic modelling and design of the demonstrator plantThe thermodynamics of the air-cycle (or the reverse ‘Joule cycle’) are adequately presented in most thermodynamic textbooks and will not be repeated For anything other than the smallest flow rates, the most efficient machines available for the necessary compression and expansion processes are Considerations for the selection of turbomachinery for air-cycle refrigeration systems have been presented and discussed by Spence et [3] a typical configuration of an air-cycle system, which is sometimes called the ‘boot-strap’ For mechanical convenience the compression process is divided into two stages, meaning that the turbine is not constrained to operate at the same speed as the primary Instead, the work recovered by the turbine during expansion is utilised in the secondary The two-stage compression also permits intercooling, which enhances the overall efficiency of the compression An ‘open system’ where the cold air is ejected directly into the cold space, removing the need for a heat exchanger in the cold In the interests of efficiency, the return air from the cold space is used to pre-cool the compressed air entering the turbine by means of a heat exchanger known as the ‘regenerator’ or the ‘recuperato ’ To support the design of the air-cycle demonstrator plant, and the selection of suitable components, a simple thermodynamic model of the air-cycle configuration shown in was The compression and expansion processes were modelled using appropriate values of isentropic efficiency, as defined in EThe heat exchange processes were modelled using values of heat exchanger effectiveness as defined in The model also made allowance for heat exchanger pressure The system COP was determined from the ratio of the cooling power delivered to the power input to the primary compressor, as defined in illustrate air-cycle performance characteristics as determined from the thermodynamic model:illustrates the variation in air-cycle COP and expander outlet temperature over a range of cycle pressure ratios for a plant operating between −20 °C and +30 °C The cycle pressure ratio is defined as the ratio of the maximum cycle pressure at secondary compressor outlet to the pressure at turbine For the ideal air-cycle, with no losses, the cycle COP increases with decreasing cycle pressure ratio and tends to infinity as the pressure ratio approaches However, the introduction of real component efficiencies means that there is a definite peak value of COP that occurs at a certain pressure ratio for a particular However,illustrates, there is a broad range of pressure ratio and duty over which the system can be operated with only moderate variation of COPThe class of turbomachinery suitable for the demonstrator plant required speeds of around 50 000 rev/ To simplify the mechanical arrangement and avoid the need for a high-speed electric motor, the two-stage compression system shown was The existing Thermo King SL200 chassis incorporated a substantial system of belts and pulleys to power circulation fans, which severely restricted the useful space available for mounting heat A simple thermodynamic model was used to assess the influence of heat exchanger performance on the efficiency of the plant so that the best compromise could be developed show the impact of intercooler and aftercooler effectiveness and pressure loss on the COP of the proposed The two-stage system in incorporated an intercooler between the two compression By dispensing with the intercooler and its associated duct work a larger aftercooler could be accommodated with improved effectiveness and reduced pressure Analysis suggested that the improved performance from a larger aftercooler could compensate for the loss of the shows the impact of the recuperator effectiveness on the COP of the plant, which is clearly more significant than that of the other heat As well as boosting cycle efficiency, increased recuperator effectiveness also moves the peak COP to a lower overall system pressure The impact of pressure loss in the recuperator is the same as for the intercooler and aftercooler shown The model did not distinguish between pressure losses in different locations; it was only the sum of the pressure losses that was Any pressure loss in connecting duct work and headers was also lumped together with the heat exchanger pressure loss and analysed as a block pressure The specific cooling capacity of the air-cycle increases with system pressure Consequently, if a higher system pressure ratio was used the required cooling duty could be achieved with a smaller flow rate of shows the mass flow rate of air required to deliver 7,5 kW of cooling power for varying system pressure Since the demonstrator system was to be based on commercially available turbomachinery, it became important to choose a pressure ratio and flow rate that could be accommodated efficiently by some existing compressor and turbine and were based on efficiencies of 81 and 85% for compression and expansion, While such efficiencies are attainable with optimised designs, they would not be realised using compromised turbocharger For the design of the demonstrator plant efficiencies of 78 and 80% were assumed to be realistically attainable for compression and Lower turbomachinery efficiencies corresponded to higher cycle pressure ratios and flow rates in order to achieve the target cooling The cycle design point was also compromised to help heat exchanger The pressure losses in duct work and heat exchangers increased in proportion with the square of flow Selecting a higher cycle pressure ratio corresponded to a lower mass flow rate and also increased density at inlet to the aftercooler heat The combined effect was a decrease in the mean velocity in the heat exchanger, a decrease in the expected pressure losses in the heat exchanger and duct work, and an increase in the effectiveness of the heat Consequently, a system pressure ratio higher than the value corresponding to peak COP was chosen in order to achieve acceptable heat exchanger performance within the available physical The below optimum performance of turbomachinery and heat exchanger components, coupled with excessive bearing losses, meant that the predicted COP of the overall system dropped to around 0, The system pressure ratio at the design point was 2,14 and the corresponding mass flow rate of air was 0,278 kg/By moving the design point beyond the pressure ratio for peak COP, it was anticipated that the demonstrator plant would yield good part-load performance since the COP would not fall as the pressure ratio was Also, operating at part-load corresponded to lower flow velocities and anticipated improvements in heat exchanger Part-load operation was achieved by reducing the speed of the primary compressor, resulting in a decrease in both pressure and mass flow rate throughout the Prime mover and primary compressorThe existing diesel engine was judged adequate to power the demonstrator The standard engine was a four cylinder, water cooled diesel engine fitted with a centrifugal clutch and all necessary ancillaries and was controlled by a microprocessor From the thermodynamic model, the pressure ratio for the primary compressor was 1, The centrifugal compressor required a shaft speed of around 55 000 rev/ Other alternatives were evaluated for primary compression with the aim of obtaining a suitable device that operated at a lower Other commercially available devices such as Roots blowers and rotary piston blowers were all excluded on the basis of poor A one-off gearbox was designed and manufactured as part of the project to step-up the engine shaft speed to around 55 000 rev/ The gearbox was a two stage, three shaft unit which mounted directly on the end of the diesel engine and was driven through the existing centrifugal Cold air unitThe secondary compressor and the expansion turbine were mounted on the same shaft in a free rotating The combination of the secondary compressor and the turbine was designated as the ‘Cold Air Unit’ (CAU) While the CAU was mechanically equivalent to a turbocharger, a standard turbocharger would not satisfy the aerodynamic requirements efficiently since the pressure ratios and inlet densities for both the compressor and the turbine were significantly different from any turbocharger Consequently, both the secondary compressor and the turbine stage were specially chosen and developed to deliver suitable Most turbochargers use plain oil fed journal bearings, which are low-cost, reliable and provide effective damping of shaft However, plain bearings dissipate a substantial amount of shaft power through viscous losses in the oil A plain bearing arrangement for the CAU was expected to absorb 2–3 kW of mechanical power, which represented around 25% of the anticipated turbine Also, the clearances in plain bearings require larger blade tip clearances for both the compressor and the turbine with a consequential efficiency Given the pressurised inlet to the secondary compressor, the limited thrust capacity of the plain bearing arrangement was also a A CAU utilising high-speed ball bearings, or air bearings, was identified as a preferable arrangement to plain Benefits would include greatly reduced bearing power losses, reduced turbomachinery tip clearance losses and increased thrust load However, adequate resources were not available to design a special one-off high speed ball bearing Consequently, a standard turbocharger plain bearing system was The secondary compressor stage was a standard turbocharger compressor selected for a pressure ratio of 1, Secondary compressor and turbine selection were linked because of the requirement to balance power and match the Since most commercial turbines are sized for high temperature (and consequently low density) air at inlet, a special turbine stage was developed for the Cost considerations precluded the manufacture of a custom turbine rotor, so a commercially available rotor was The standard turbine rotor blade profile was substantially modified and vaned nozzles for turbine inlet were designed to match the modified rotor, in line with previous turbine investigations at QUB (Spence and Artt,) An exhaust diffuser was also incorporated into the turbine stage in order to improve turbine efficiency and to moderate the exhaust noise levels through reduced air The exhaust diffuser exited into a specially designed exhaust The performance of the turbine stage was measured before the unit was incorporated into the complete demonstrator The peak efficiency of the turbine was established at 81% Heat exchangersDue to packaging constraints, the heat exchangers had to be specially designed with careful consideration being given to heat exchanger position and header geometry in an attempt to achieve the best performance from the heat Tube and fin aluminium heat exchangers, similar to those used in automotive intercooler applications, were chosen primarily because they could be produced on a ‘one-off’ basis at a reasonable There were other heat exchanger technologies available that would have yielded better performance from the available volume, but high one-off production costs precluded their use in the demonstrator Several different tube and fin heat exchangers were tested and used to validate a computational Once validated, the model was used to assess a wide range of possible heat exchanger configurations that could fit within the Thermo King SL200 Fitting the proposed heat exchangers within the existing chassis and around the mechanical drive system for the circulation fans, but while still achieving the necessary heat exchanger performance was very It was clear that potential heat exchanger performance was being sacrificed through the choice of tube and fin construction and by the constraints of the layout of the existing SL200 The final selection comprised two separate aftercooler units, while the single recuperator was a large, triple pass Based on laboratory tests and the heat exchanger model, the anticipated effectiveness of both the recuperator and aftercooler units was 80% InstrumentationA range of conventional pressure and temperature instrumentation was installed on the air-cycle demonstrator Air temperature and pressure was logged at inlet and outlet from each heat exchanger, compressor and the The speed of the primary compressor was determined from the speed measurement on the diesel engine control unit, while the cold air unit was equipped with a magnetic speed No air flow measurement was included on the demonstrator Instead, the air flow rate was deduced from the previously obtained turbine performance map using the measurements of turbine pressure ratio and rotational System testingDuring some preliminary tests a heat load was applied and the functionality of the demonstrator plant was Having assessed that it was capable of delivering approximately the required performance, the plant was transported to a Thermo King calorimeter test facility specifically for measuring the performance of transport refrigeration The calorimeter was ideally suited for accurately measuring the refrigeration capacity of the air-cycle demonstrator The calorimeter was operated according to standard ARI 1100-2001; the absolute accuracy was better than 200W and all auxiliary instrumentation was calibrated against appropriate The performance capacity of transport refrigeration units is generally rated at two operating conditions; 0 and −20 °C, and both at an ambient temperature of +30 °C Along with the specified operating conditions of 0 and −20 °C, a further part-load condition at −20 °C was Considering that the air-cycle plant was only intended to demonstrate a concept and that there were concerns about the reliability of the gearbox and the cold air unit thrust bearing, it was decided to operate the plant only as long as was necessary to obtain stabilised measurements at each operating The demonstrator plant operated satisfactorily, allowing sufficient measurements to be obtained at each of the three operating The recorded performance is summarised In total, the unit operated for approximately 3 h during the course of the various While the demonstrator plant operated adequately to allow measurements, some smoke from the oil system breather suggested that the thrust bearing of the CAU was heavily overloaded and would fail, as had been anticipated at the design Testing was concluded in case the bearing failed completely causing the destruction of the entire CAU There was no evidence of any gearbox deterioration during Discussion of measured performanceFrom the calorimeter performance measurements, the primary objective of the project had been A unique air-cycle refrigeration system had been developed within the same physical envelope as the existing Thermo King SL200 refrigeration unit, w
《暖通空调》是本杂志，本专业的核心期刊，自己去随便下载几篇都是暖通行业相关的。 翻译借助百度翻译和自己那点水平，这小事儿还用求助要原创的我可以提供
告诉你一个秘密。。。去谷歌搜一下 HAVC
高职院校“供热通风与空调工程技术专业”实训室的建设摘 要：高职高专院校实训基地是培养职业实践能力的核心条件，而实训室是组织实践教学、强化技能培养、实现人才培养目标的重要基地。建立满足基于“工作过程”项目导向教学的实训室是必要，能保证学生在校期间学习有一个真实的工作环境，为培养学生的技术应用能力提供保证。实训室应具有高新的技术内涵、逼真的实训环境、完备的设备配置、配套的实训教材、科学的组织管理。关键词：高职教育；竞争力；能力；素质由于我国的高等职业教育在起步较晚，其人才培养模式基本上是以学科为核心的普通教育模式，强调培养的学生具有扎实的理论基础、具有一定的研究和设计能力，还没有完全形成培养职业人才的教育体系和教育模式。相应的实验室也满足不了培养职业人才的要求。现有高职院校的实验室基本上是本科和中专学校的原有实验室，而本科院校的实验室是以理论研究和验证为主，中专学校的实验室是以教学演示为主，两者均缺乏培养学生动手操作能力、分析和解决问题能力的功能。如何搞好高等职业院校实验室建设，使其能更好地为教学服务以满足培养高素质职业人才的要求，是迫切需要解决的问题。我院的“供热通风与卫生工程技术”专业为中德联合办学的首批试点专业，省级重点专业。通过与德国专家的全面合作，我们制定了“面向实践的课程”体系和人才培养模式。该课程体系打破了传统的“老三段”式的教学模式，把和专业教学有关的“基础课”、“专业基础课”和“专业课”合并成“职业技术课”，所有“职业技术课”按专业特点进行整合，分别在“供热”、“给排水”和“通风空调”三个实验室内组织教学。因此，这三个实验室的建设对课程体系的改革至关重要。下面就这三个实验室的建设谈谈自己的看法。 1 应以服务课堂教学为建设宗旨原来的课堂教学大多数是在教室内进行，实验室内进行的教学演示实验和验证实验相对很少，即使建设了设备先进的实验室，对课堂教学来讲，利用率也是极低的，造成了资源的大量浪费。由于人才培养模式的不同，工科高等职业院校实验室的建设与同类型的本科院校有很大差异，它不需要过多地进行教学演示实验和验证实验，其重点应放在为课堂教学服务上。通过对高职的人才培养模式的研究和借鉴德国的成功经验，我们制定了一个既能适应“面向实践的课程”体系又能提高实验设备的利用率的教学实验室的建设计划，该计划的最大特点是将课堂教学改在实验室内进行，即把实验室作为课堂教学的主要场所，这就要求实验室除满足实验教学外更主要的应满足课堂教学要求。这样的实验室与传统的实验室有很大的不同，实验室的功能、系统的组成、设备的布置等都有较大变化。“供热通风与卫生工程技术”专业的教学内容，主要是讲授“供热”、“给排水”和“通风空调”系统的组成和分类、热力和水力计算、设备选型计算、安装及运行管理等方面的知识。按三大系统建立三个实验室，分三条教学主线组织教学，所有的专业教学均在三个实验室内进行。三个实验室分别建有各种类型的供热系统、给水排水系统、通风空调系统，教师在实验室内参照各种系统讲授、提出问题并和学生一同解决问题。这样的教学与传统的学科教学相比很多优点。第一，教学直观方便，系统中所有的设备、管路、附件、仪表均为实物就地安装，教师按实物讲解它们的构造、工作原理、安装位置等，既方便又直观。第二，系统的整体感较强，系统中所有的设备、管路、附件、仪表均安装在同一实验室内，使学生一眼就能看出系统的整体结构，不存在传统的学科教学中首尾分离的现象。第三，教学过程中师生可以互动，能充分调动学生学习的积极性。 2 应注重学生动手能力、分析和解决问题能力的培养工科高等职业院校主要培养的是技术应用型人才，学生应具有较强的动手操作能力、分析和解决问题的能力，而这些能力的培养主要是在校内学习期间完成的。培养学生动手能力、分析和解决问题能力可以有很多途径，除了参加社会实践、毕业实习外，在校内建立高标准的实验、实训基地是最为有效的方法。我们的实验室建设从一开始构思就把学生动手能力、分析问题和解决问题能力的培养问题放在了首位。从实验室整体设计到系统某一局部的细化处理处处都考虑上述问题，贯穿始终。如“供热实验室”设计时，我们首先考虑把系统中的供热热源、泵站、热力分配站、热用户用管道连接组合成一个完整的、实际的供热系统，系统中安装有各种管路附件、热工检测和控制仪表、实验用仪表等。锅炉点火、水泵启动这个系统就可以运行。而过去的这些实验室（台）均是独立的，没有形成整体。学生可以通过锅炉点火、水泵启动、锅炉烟气测定、热工和水力参数检测、维护管理等培养其动手操作能力。由于系统是一个实际运行的整体，各设备、附件、仪表相互关联，可以通过系统运行、参数调节及人为故障设定等培养学生分析问题、解决问题的能力。这在过去的课堂上和分散的实验室里是绝对做不到的。 3 应密切结合生产实际我们培养学生的目标是毕业即顶岗、毕业即就业，也就是说学生毕业到工作单位后能够胜任自己的工作。对“供热通风与卫生工程技术”专业来讲，毕业生应能独立完成一般的安装工程施工、施工管理及暖通空调系统运行管理等工作。为了达到这一目标，所建设的实验室要和生产实际紧密结合。我们实验室内安装的系统应为生产实际中常见的系统，所选的设备应为生产实际中常用的设备，并且尽可能采用新工艺、新材料、新设备，也就是说实验室内的系统、设备和材料要比生产实际所采用的要更好更新。这就要求教师除正常教学外，要积极参加本专业的学术活动，及时了解本专业的新技术和新工艺，更好的服务于教学。 4 加强厂校合作，保证设备及时更新实验室建成后，经过一段时间的使用，随着技术的进步，其系统和设备就要落后，如何对落后的技术和设备进行更新，是每一个实验室都要面对的问题。与其他专业不同，暖通工程中使用的设备种类繁多且更新较快。为了使我们的实验室能更好地服务于教学、服务于生产，就要求其系统、设备和材料按工程实际不断地进行更新，对于学校来讲这是一笔不小的费用。我们的做法是，利用我们的技术优势和生产厂家的设备资源，积极开展厂校合作，互惠互利，及时更新实验设备。比如某厂家生产出了新型的设备，可免费安装在我们的实验室内，生产厂家可以以我们的实验室作为基地，进行产品宣传、组织用户参观、对用户进行安装和运行等方面的培训。我们也可以免费为他们进行性能测试、产品鉴定等。通过这种合作方式使我们和生产厂家都受益，真正实现了互惠互利。目前我们已经和多个生产厂家达成了这样的协议。实践教学是达到教学要求、实现培养目标、保证教学质量、提高教学效益的重要环节，必须科学合理建立相应的专业实验实训室及其配套管理机制。建设好高职院校专业实验实训室，提高学生综合技能，提高就业率，是所有高职院校领导和老师的期望，是企业、社会进行市场竞争的需要，需要建设者付出大量辛勤的劳动和汗水。
区域供热，如果你是搞采暖的
可以写作
你是学建筑环境也设备工程的不
多少字啊？什么方向的
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 The term cooling refers generally to any natural or artificial process by which heat is The process of artificially producing extreme cold temperatures is referred to as Cold is the absence of heat, hence in order to decrease a temperature, one "removes heat", rather than "adding " In order to satisfy the Second Law of Thermodynamics, some form of work must be performed to accomplish This work is traditionally done by mechanical work but can also be done by magnetism, laser or other However, all refrigeration uses the three basic methods of heat transfer: convection, conduction, or Historical applicationsIce harvestingThe use of ice to refrigerate and thus preserve food goes back to prehistoric Through the ages, the seasonal harvesting of snow and ice was a regular practice of most of the ancient cultures: Chinese, Hebrews, Greeks, Romans, P Ice and snow were stored in caves or dugouts lined with straw or other insulating The Persians stored ice in pits called Rationing of the ice allowed the preservation of foods over the cold This practice worked well down through the centuries, with icehouses remaining in use into the twentieth In the 16th century, the discovery of chemical refrigeration was one of the first steps toward artificial means of Sodium nitrate or potassium nitrate, when added to water, lowered the water temperature and created a sort of refrigeration bath for cooling In Italy, such a solution was used to chill During the first half of the 19th century, ice harvesting became big business in A 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 First refrigeration systemsThe first known method of artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled , absorbing heat from the surrounding The experiment even created a small amount of ice, but had no practical application at that 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 In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low An American living in Great Britain, Jacob Perkins, obtained the first patent for a vapor-compression refrigeration system in Perkins built a prototype system and it actually worked, although it did not succeed In 1842, an American physician, John Gorrie, designed the first system for refrigerating water to produce He also conceived the idea of using his refrigeration system to cool the air for comfort in homes and hospitals (, 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 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 US Patent Office in Gorrie built a working prototype, but his system was a commercial Alexander Twining began experimenting with vapor-compression refrigeration in 1848 and obtained patents in 1850 and He is credited with having initiated commercial refrigeration in the United States by 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 G His first commercial ice-making machine followed in 1854 and his patent for an ether liquid-vapour compression refrigeration system was granted in Harrison introduced commercial vapor-compression refrigeration to breweries and meat packing houses and by 1861, a dozen of his systems were in 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 AThe 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 Due to the toxicity of ammonia, such systems were not developed for use in homes, but were used to manufacture ice for 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 Thaddeus Lowe, an American balloonist from the Civil War, had experimented over the years with the properties of One of his mainstay enterprises was the high-volume production of hydrogen He also held several patents on ice making His "Compression Ice Machine" would revolutionize the cold storage 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 Y 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 Domestic mechanical refrigerators became available in the United States around Widespread commercial useBy the 1870s breweries had become the largest users of commercial refrigeration units, though some still relied on harvested 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 Eventually breweries began to complain of tainted This raised demand for more modern and consumer-ready refrigeration and ice-making 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 Refrigerated railroad cars were introduced in the US in the 1840s for the short-run transportation of dairy In 1867 JB 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 By 1900 the meat packing houses of Chicago had adopted ammonia-cycle commercial By 1914 almost every location used artificial 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 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 Most modern refrigerators keep the temperature between -40 and +20 °C and have a maximum payload of around 24 000 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 Freon is a trademark of the Dupont Corporation and refers to these CFC, and later hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC), 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 The intent was to provide refrigeration equipment for home use without endangering the lives of the These CFC refrigerants answered that The Montreal ProtocolAs of 1989, CFC-based refrigerant was banned via the Montreal Protocol due to the negative effects it has on the ozone The Montreal Protocol was ratified by most CFC producing and consuming nations in Montreal, Quebec, Canada in September 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 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 G[citation needed]The tenets of the Montreal Protocol were put into effect in the United States via the Clean Air Act legislation in August The Clean Air Act was further amended in 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 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 In July 1992, the EPA made illegal the venting of CFC and HCFC In June 1993, the EPA required that major leaks in refrigeration systems be fixed within 30 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 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 In August 1993, the EPA implemented reclamation requirements for 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 In November 1993, the EPA required that all refrigerant recovery equipment meet the standards of ARI 740- In November 1995, the EPA also restricted the venting of HFC 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 In December 1995, CFC refrigerant importation and production in the US was It is currently planned to ban all HCFC refrigerant importation and production in the year 2030, although that will likely be 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 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 In commerce and manufacturing, there are many uses for Refrigeration is used to liquify gases like oxygen, nitrogen, propane and methane for In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture 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 In transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes and sea-going vessels, refrigeration is a 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 Meats, poultry and fish all must be kept in climate-controlled environments before being Refrigeration also helps keep fruits and vegetables edible One of the most influential uses of refrigeration was in the development of the sushi/sashimi industry in J 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 J 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 Methods of refrigerationMethods of refrigeration can be classified as non-cyclic, cyclic and Non-cyclic refrigerationIn these methods, refrigeration can be accomplished by melting ice or by subliming dry These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable 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 55 kJ/kg ( 144 Btu/lb) of Foodstuffs maintained at this temperature or slightly above have an increased storage Solid carbon dioxide, known as dry ice, is used also as a Having no liquid phase at normal atmospheric pressure, it sublimes directly from the solid to vapor phase at a temperature of -5 °C (-3 °F) Dry ice is effective for maintaining products at low temperatures during the period of 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 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 This satisfies the second law of A refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and rejects heat as it circulates through a 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 Heat naturally flows from hot to 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 Insulation is used to reduce the work and energy required to achieve and maintain a lower temperature in the cooled The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in 1824 as a heat 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 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