Refrigeration 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. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in 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. Cryogenics is often used incorrectly to refer to Cryonics, cryopreserving humans or animals

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. The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which This work is traditionally done by mechanical work but can also be done by magnetism, laser or other means. In Physics, mechanical work is the amount of Energy transferred by a Force. However, all refrigeration uses the three basic methods of heat transfer: convection, conduction, or radiation. In thermal physics, heat transfer is the passage of Thermal energy from a hot to a colder body Convection in the most general terms refers to the movement of molecules within Fluids (i Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature.

Contents 1 Historical applications 1.1 Ice harvesting 1.2 First refrigeration systems 1.3 Widespread commercial use 1.4 Home and consumer use 1.5 The Montreal Protocol 2 Current applications of refrigeration 3 Methods of refrigeration 3.1 Non-cyclic refrigeration 3.2 Cyclic refrigeration 3.2.1 Vapor-compression cycle 3.2.2 Vapor absorption cycle 3.2.3 Gas cycle 3.3 Thermoelectric refrigeration 3.4 Magnetic refrigeration 3.5 Other methods 4 Unit of refrigeration 5 See also 6 References 7 Additional reading 8 External links

Historical applications

Ice harvesting

The use of ice to refrigerate and thus preserve food goes back to prehistoric times. Ice is a Solid phase, usually crystalline, of a Non-metalic substance that is liquid or gas at Room temperature, such as Ammonia ^[1][2] 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. A dugout or dug-out, also known as a pithouse Pit-house, earth-house, mud hut, is a shelter for humans or domestic animals based on a hole Straw is an agricultural By-product, the dry stalk of a Cereal plant after the Grain or Seed has been removed 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. Ice houses were buildings used to store Ice throughout the year prior to the invention of the Refrigerator.

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. Sodium nitrate is the Chemical compound with the formula NaNO3 Potassium nitrate is a Chemical compound with the Chemical formula K[[Nitrogen N]] O 3 In Italy, such a solution was used to chill wine. ^[3]

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. History See also History of New England New England's earliest inhabitants were Algonquian -speaking Native Americans including the Frederic Tudor ( September 4, 1783 - February 6, 1864) was Boston 's "Ice King" the founder of the Tudor Ice Company The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer

First refrigeration systems

The first known method of artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in 1748. William Cullen ( 15 April 1710 – 5 February 1790) was a Scottish doctor and Chemist. Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled , absorbing heat from the surrounding air. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. Diethyl ether, also known as ether and ethoxyethane, is a clear colorless and highly Flammable liquid with a low Boiling point and a The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid The enthalpy of vaporization, (symbol \Delta{}_{v}H also known as the heat of vaporization or heat of evaporation, is the Energy required 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. Oliver Evans ( 13 September, 1755 &ndash 15 April, 1819) was a United States Inventor. Vapor-compression refrigeration is one of the many Refrigeration cycles available for use

In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low temperatures. Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor

An American living in Great Britain, Jacob Perkins, obtained the first patent for a vapor-compression refrigeration system in 1834. Jacob Perkins ( 9 July 1766 &ndash 30 July 1849) was an Anglo-American Inventor, Mechanical engineer and Physicist Perkins built a prototype system and it actually worked, although it did not succeed commercially. ^[4]

In 1842, an American physician, John Gorrie, designed the first system for refrigerating water to produce ice. John Gorrie, ( October 3, 1802 &ndash June 29, 1855) physician scientist inventor and humanitarian is considered the father of 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. A gas compressor is a mechanical device that increases the Pressure of a Gas by reducing its Volume. 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. In Thermodynamics, an isentropic process ( iso = "equal" (Greek Entropy = "disorder" is one during which the entropy of the system The United States Patent and Trademark Office ( PTO or USPTO) is an agency in the United States Department of Commerce that issues Patents to ^[5] 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. James Harrison (April 1816 - September 3 1893 was a Scottish newspaper printer journalist politician and pioneer in the field of mechanical 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. For a topic outline on this subject see List of basic Australia topics. For a topic outline on this subject see List of basic Argentina topics. The United States of America —commonly referred to as the William Soltau Davidson ( 15 June 1846- 17 July 1924 was the New Zealand pioneer of refrigerated Shipping. New Zealand is an Island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island Dunedin (1876&ndash82 was the first ship to complete a truly successful transport of refrigerated meat Australasia is a Region of Oceania: New Zealand, Australia, Papua New Guinea, and neighbouring Islands in the Pacific South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a

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. The absorption refrigerator is a Refrigerator that utilizes a heat source (e 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. An Icebox was the common appliance for providing Refrigeration in the home before safe refrigerants made compact mechanical Refrigerators useful Ice houses were buildings used to store Ice throughout the year prior to the invention of the Refrigerator.

Thaddeus Lowe, an American balloonist from the Civil War, had experimented over the years with the properties of gases. Thaddeus Sobieski Constantine Lowe ( August 20, 1831 - January 16, 1913) also known as Professor T One of his mainstay enterprises was the high-volume production of hydrogen gas. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 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. A refrigerator (often called a " fridge " for short is a cooling appliance comprising a thermally insulated compartment and a Heat pump - ^[6]

Widespread commercial use

By 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. Professor Doctor Carl Paul Gottfried von Linde ( 11 June, 1842 - 16 November 1934) was a German engineer who developed Refrigeration

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. Armour and Company was an American Slaughterhouse and meatpacking company founded in Chicago Illinois, in 1867 by the Armour brothers led by

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 use

With 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 Protocol

As of 1989, CFC-based refrigerant was banned via the Montreal Protocol due to the negative effects it has on the ozone layer. For other similarly-named agreements see Montreal Convention (disambiguation. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 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. Greenpeace, originally known as the Greenpeace Foundation, was founded in Vancouver, British Columbia, Canada in 1972 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. Greenpeace, originally known as the Greenpeace Foundation, was founded in Vancouver, British Columbia, Canada in 1972

The tenets of the Montreal Protocol were put into effect in the United States via the Clean Air Act legislation in August 1988. The United States of America —commonly referred to as the The 1990 Clean Air Act is a piece of United States environmental policy relating to the reduction of Smog and Air pollution. 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^[7], detailing how chlorine in CFC and HCFC refrigerants adversely affected the ozone layer. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane 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 refrigeration

Probably 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. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Propane is a three- Carbon Alkane, normally a gas but compressible to a liquid that is transportable Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture content. Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase 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). An oil refinery is an industrial Process plant where Crude oil is processed and refined into more useful Petroleum products, such as Gasoline A chemical plant is industrial process plant that manufactures (or otherwise processes Chemicals usually on a large scale Petrochemicals are chemical products made from raw materials of Petroleum or other Hydrocarbon origin Alkylation is the transfer of an Alkyl group from one Molecule to another Isomers Among the molecules which have the Chemical formula 48 four Isomers are Alkenes. Butane, also called n -butane, is the unbranched Alkane with four Carbon Atoms CH3CH2CH2CH3 The octane rating is a measure of the resistance of Gasoline and other Fuels to Detonation ( Engine knocking) in spark-ignition 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. Hepatitis A, (formerly known as infectious hepatitis) is an acute Infectious disease of the Liver caused by Hepatitis A virus which is 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. The is currently a Japanese multinational manufacturer and marketer of high-quality Vacuum flasks and Consumer electronics including Electric

Methods of refrigeration

Methods of refrigeration can be classified as non-cyclic, cyclic and thermoelectric.

Non-cyclic refrigeration

In these methods, refrigeration can be accomplished by melting ice or by subliming dry ice. Ice is a Solid phase, usually crystalline, of a Non-metalic substance that is liquid or gas at Room temperature, such as Ammonia Sublimation of an element or compound is a transition from the Solid to Gas phase with no intermediate liquid stage Dry ice is solid Carbon dioxide. It is commonly used as a versatile cooling agent These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable coolers. A cooler ( portable ice chest) most commonly is an insulated box and is used to keep Food or Drink cool

Ice owes its effectiveness as a cooling agent to its constant melting point of 0 °C (32 °F). The melting point of a solid is the temperature range at which it changes state from solid to Liquid. 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. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single 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 refrigeration

Main article: Heat pump and refrigeration cycle

This 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. Thermodynamic heat pump and refrigeration cycles are the models for Heat pumps and Refrigerators. A thermodynamic cycle is a series of Thermodynamic processes which returns a system to its initial state 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. The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which

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. A refrigerator (often called a " fridge " for short is a cooling appliance comprising a thermally insulated compartment and a Heat pump - 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. In Physics, mechanical work is the amount of Energy transferred by a Force. Insulation is used to reduce the work and energy required to achieve and maintain a lower temperature in the cooled space. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in 1824 as a heat engine. Nicolas Léonard Sadi Carnot (1 June 1796 &ndash 24 August 1832 was a French Physicist and Military engineer who in his 1824 Reflections A Carnot heat engine is a hypothetical engine that operates on the reversible Carnot cycle.

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. Vapor-compression refrigeration is one of the many Refrigeration cycles available for use The absorption refrigerator is a Refrigerator that utilizes a heat source (e

Cyclic refrigeration can be classified as:

1. Vapor cycle, and
2. Gas cycle

Vapor cycle refrigeration can further be classified as:

1. Vapor compression refrigeration
2. Vapor absorption refrigeration

Vapor-compression cycle

(See Heat pump and refrigeration cycle and Vapor-compression refrigeration for more details)

The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems. Vapor-compression refrigeration is one of the many Refrigeration cycles available for use The absorption refrigerator is a Refrigerator that utilizes a heat source (e Thermodynamic heat pump and refrigeration cycles are the models for Heat pumps and Refrigerators. Vapor-compression refrigeration is one of the many Refrigeration cycles available for use Figure 1 provides a schematic diagram of the components of a typical vapor-compression refrigeration system.

The thermodynamics of the cycle can be analyzed on a diagram^[8][9] as shown in Figure 2. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " In this cycle, a circulating refrigerant such as Freon enters the compressor as a vapor. A gas compressor is a mechanical device that increases the Pressure of a Gas by reducing its Volume. From point 1 to point 2, the vapor is compressed at constant entropy and exits the compressor superheated. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy See Superheater for the device used in Steam engines In Physics, superheating (sometimes referred to as boiling retardation From point 2 to point 3 and on to point 4, the superheated vapor travels through the condenser which first cools and removes the superheat and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature. For other Condensers not involving heat transfer see Condenser (disambiguation Between points 4 and 5, the liquid refrigerant goes through the expansion valve (also called a throttle valve) where its pressure abruptly decreases, causing flash evaporation and auto-refrigeration of, typically, less than half of the liquid. A thermostatic expansion valve (often abbreviated as TXV or TX valve is a component in Refrigeration and Air conditioning systems that controls the amount of superheat Flash (or partial Evaporation is the partial Vaporization that occurs when a saturated liquid stream undergoes a reduction in pressure by passing through

That results in a mixture of liquid and vapor at a lower temperature and pressure as shown at point 5. The cold liquid-vapor mixture then travels through the evaporator coil or tubes and is completely vaporized by cooling the warm air (from the space being refrigerated) being blown by a fan across the evaporator coil or tubes. The resulting refrigerant vapor returns to the compressor inlet at point 1 to complete the thermodynamic cycle.

The above discussion is based on the ideal vapor-compression refrigeration cycle, and does not take into account real-world effects like frictional pressure drop in the system, slight thermodynamic irreversibility during the compression of the refrigerant vapor, or non-ideal gas behavior (if any). For articles on other forms of reversibility including reversibility of microscopic dynamics see Reversibility (disambiguation. These four properties that constitute an ideal gas can be easily remembered by the acronym RIPE which stands for - R andom Motion (molecules are in constant random motion

More information about the design and performance of vapor-compression refrigeration systems is available in the classic "Perry's Chemical Engineers' Handbook". Perry's Chemical Engineers' Handbook was first published in 1934 and the most current eighth edition was published in October 2007. ^[10]

Vapor absorption cycle

(See Gas absorption refrigerator for more details)

In the early years of the twentieth century, the vapor absorption cycle using water-ammonia systems was popular and widely used but, after the development of the vapor compression cycle, it lost much of its importance because of its low coefficient of performance (about one fifth of that of the vapor compression cycle). The absorption refrigerator is a Refrigerator that utilizes a heat source (e The coefficient of performance, or COP (sometimes CP of a Heat pump is the ratio of the change in Heat at the "output" (the heat reservoir of interest Nowadays, the vapor absorption cycle is used only where waste heat is available, where heat is derived from solar collectors, or electricity is unavailable. A solar collector is a device for extracting the Energy of the Sun not indirectly into a more usable or storable form

The absorption cycle is similar to the compression cycle, except for the method of raising the pressure of the refrigerant vapor. In the absorption system, the compressor is replaced by an absorber which dissolves the refrigerant in a suitable liquid, a liquid pump which raises the pressure and a generator which, on heat addition, drives off the refrigerant vapor from the high-pressure liquid. Some work is required by the liquid pump but, for a given quantity of refrigerant, it is much smaller than needed by the compressor in the vapor compression cycle. In an absorption refrigerator, a suitable combination of refrigerant and absorbent is used. The most common combinations are ammonia (refrigerant) and water (absorbent), and water (refrigerant) and lithium bromide (absorbent). Lithium bromide, or LiBr is a Chemical compound of Lithium and Bromine.

Gas cycle

When the working fluid is a gas that is compressed and expanded but doesn't change phase, the refrigeration cycle is called a gas cycle. Air is most often this working fluid. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five As there is no condensation and evaporation intended in a gas cycle, components corresponding to the condenser and evaporator in a vapor compression cycle are the hot and cold gas-to-gas heat exchangers in gas cycles. A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media

The gas cycle is less efficient than the vapor compression cycle because the gas cycle works on the reverse Brayton cycle instead of the reverse Rankine cycle. The ' Brayton cycle' is a constant-pressure cycle that describes the workings of the Gas turbine engine basis of the Jet engine and others The Rankine cycle is a thermodynamic cycle which converts heat into work As such the working fluid does not receive and reject heat at constant temperature. In the gas cycle, the refrigeration effect is equal to the product of the specific heat of the gas and the rise in temperature of the gas in the low temperature side. Therefore, for the same cooling load, a gas refrigeration cycle will require a large mass flow rate and would be bulky.

Because of their lower efficiency and larger bulk, air cycle coolers are not often used nowadays in terrestrial cooling devices. The air cycle machine is very common, however, on gas turbine-powered 'jet' aircraft because compressed air is readily available from the engines' compressor sections. An air cycle machine ( ACM) is the refrigeration unit of the Environmental control system used in pressurized A gas turbine, also called a combustion turbine, is a rotary Engine that extracts energy from a flow of Combustion gas These jet aircraft's cooling and ventilation units also serve the purpose of pressurizing the aircraft.

Thermoelectric refrigeration

Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. Thermoelectric cooling uses the Peltier effect to create a Heat flux between the junction of two different types of materials The thermoelectric effect is the direct conversion of temperature differences to electric Voltage and vice versa In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks This effect is commonly used in camping and portable coolers and for cooling electronic components and small instruments.

Magnetic refrigeration

Main article: Magnetic refrigeration

Magnetic refrigeration, or adiabatic demagnetization, is a cooling technology based on the magnetocaloric effect, an intrinsic property of magnetic solids. Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. The term intrinsic denotes a characteristic or property of some thing or action which is essential and specific to that thing or action and which is wholly independent The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate. Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field Salt is a Dietary mineral composed primarily of Sodium chloride that is essential for Animal life but toxic to most land plants Cerium (ˈsɪəriəm is a Chemical element with the symbol Ce and Atomic number 58 Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 In Inorganic chemistry, a nitrate is a salt of Nitric acid with an Ion composed of one Nitrogen and three Oxygen atoms The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a An electron shell may be crudely thought of as an Orbit followed by Electrons around an Atom nucleus.

A strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy A heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off. This increases the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the heat sink.

Because few materials exhibit the required properties at room temperature, applications have so far been limited to cryogenics and research. Cryogenics is often used incorrectly to refer to Cryonics, cryopreserving humans or animals

Other methods

Other methods of refrigeration include the Air cycle machine used in aircraft; the Vortex tube used for spot cooling, when compressed air is available; and Thermoacoustic refrigeration using sound waves in a pressurised gas to drive heat transfer and heat exchange. An air cycle machine ( ACM) is the refrigeration unit of the Environmental control system used in pressurized For the term 'vortex-tube' used in Fluid dynamics please see Vorticity The vortex tube, also known as the Ranque-Hilsch vortex Thermoacoustic hot air engines ( Sonic heat pump and refrigeration or thermoacoustic heat pump and refrigeration) of which nearly all are thermoacoustic stirling

Unit of refrigeration

Domestic and commercial refrigerators may be rated in kJ/s, or Btu/h of cooling. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity Commercial refrigerators in the US are mostly rated in tons of refrigeration, but elsewhere in kW. Units of mass There are three similar units of Mass called the ton: Long ton (simply ton in countries such as the United One ton of refrigeration capacity can freeze one short ton of water at 0 °C (32 °F) in 24 hours. The short ton ( S/T) is a unit of mass equal to 2000 lb (around 907 Based on that:

Latent heat of ice (i. e. , heat of fusion) = 333. The standard Enthalpy of fusion (symbol \Delta{}H_{fus} also known as the heat of fusion or specific melting heat, is the amount of 55 kJ/kg ≈ 144 Btu/lb

One short ton = 2000 lb

Heat extracted = (2000)(144)/24 hr = 288000 Btu/24 hr = 12000 Btu/hr = 200 Btu/min

1 ton refrigeration = 200 Btu/min = 3. The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass 517 kJ/s = 3. 517 kW^[11]

A much less common definition is: 1 tonne of refrigeration is the rate of heat removal required to freeze a metric ton (i. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. This article is about the tonne or metric ton For other tons see Ton. This article is about the tonne or metric ton For other tons see Ton. e. , 1000 kg) of water at 0 °C in 24 hours. The Celsius Temperature scale was previously known as the centigrade scale. Based on the heat of fusion being 333. The standard Enthalpy of fusion (symbol \Delta{}H_{fus} also known as the heat of fusion or specific melting heat, is the amount of 55 kJ/kg, 1 tonne of refrigeration = 13,898 kJ/h = 3. 861 kW. As can be seen, 1 tonne of refrigeration is 10% larger than 1 ton of refrigeration.

Most residential air conditioning units range in capacity from about 1 to 5 tons of refrigeration.

See also

Einstein refrigerator Freezer Heat pump Heating, Ventilating and Air-conditioning Icebox Ice cream van Icyball

Laser cooling Pot-in-pot refrigerator Refrigerant Refrigeration cycle Refrigerator Refrigerator car Reefer (ship)

Reefer (container) Seasonal energy efficiency ratio (SEER) Timeline of low-temperature technology Vapor-compression refrigeration Coolgardie safe

References

Additional reading

• Refrigeration volume, ASHRAE Handbook, ASHRAE, Inc. The ASHRAE Handbook is the four-volume Flagship publication of the nonprofit technical organization American Society of Heating Refrigerating and Air-Conditioning , Atlanta, GA
• Stoecker and Jones, Refrigeration and Air Conditioning, Tata-McGraw Hill Publishers
• Mathur, M. L. , Mehta, F. S. , Thermal Engineering Vol II
• MSN Encarta Encyclopedia
• Andrew D. Althouse, Carl H. Turnquist, Alfred F. Bracciano (2003). Modern Refrigeration and Air Conditioning, 18th Edition, Goodheart-Wilcox Publishing. ISBN 1590702808.  
• Anderson, Oscar Edward (1972). Refrigeration in America: A history of a new technology and its impact. Kennikat Press, 344. ISBN 0804616213.  
• Shachtman, Tom (2000-12-12). Absolute Zero: And the Conquest of Cold. Mariner Books, 272. ISBN 0618082395.  
• Woolrich, Willis Raymond (1967). The men who created cold: A history of refrigeration,, [1st ed. ], Exposition Press, 212.  

External links

• "The Refrigeration Cycle", from HowStuffWorks
• American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
• British Institute of Refrigeration
• Refrigerant Recovery Environment Services
• "Notes on vapor-compression refrigeration", Queens University (Canada)
• "The ideal vapor compression refrigeration cycle", University of Nevada (US)
• Refrigeration History
• Scroll down to "Continuous-Cycle Absorption System"
• US Department of Energy: Technology Basics of Absorption Cycles
• Calendar of Inventive Contributors to the Development of Refrigeration, 1748-1885, a short history of the evolution of the refrigerator.
• Refrigeration (from The Handbook of Texas Online)

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