| Absorption chillers | are air-conditioning systems based on absorption refrigeration, and they perform best when the heat source can supply heat at a high temperature with little temperature drop.
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| Absorption refrigeration systems | involve the absorption of a refrigerant by a transport medium. The most widely used absorption refrigeration system is the ammonia-water system, where ammonia (NH3) serves as the refrigerant and water (H2O) as the transport medium. Absorption refrigeration systems are economically attractive when there is a source of inexpensive heat energy at a temperature of 100 to 200°C. Some examples of inexpensive heat energy sources include geothermal energy, solar energy, and waste heat from cogeneration or process steam plants, and even natural gas when it is available at a relatively low price.
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| Carnot heat pump | is a heat pump that operates on the reversed Carnot cycle. When operating between the two thermal energy reservoirs at temperatures TL and TH the Carnot heat pump can have a coefficient of performance of COPHP, rev = 1/ (1 – TL / TH) = TH / (TH – TL).
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| Carnot refrigerator | is a refrigerator that operates on the reversed Carnot cycle. When operating between the two thermal energy reservoirs at temperatures TL and TH the Carnot refrigerator can have a coefficient of performance of COPR, rev = 1/ (TH / TL – 1) = TL / (TH – TL).
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| Cascade refrigeration cycles | perform the refrigeration process in stages, that is, to have two or more refrigeration cycles that operate in series.
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| Coefficient of performance(COP) | is the measure of performance of refrigerators and heat pumps. It is expressed in terms of the desired result for each device (heat absorbed from the refrigerated space for the refrigerator or heat added to the hot space by the heat pump) divided by the input, the energy expended to accomplish the energy transfer (usually work input).
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| Cooling capacity | is the rate of heat removal from the refrigerated space by a refrigeration system.
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| Frosting | which occurs in humid climates when the temperature falls below 2 to 5°C, is the major problem with air-source systems. The frost accumulation on the evaporator coils is highly undesirable since it seriously disrupts heat transfer. The coils can be defrosted, however, by reversing the heat pump cycle (running it as an air conditioner). This results in a reduction in the efficiency of the system.
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| Gas refrigeration cycle | is based onthe reversed Brayton cycle where the compressor exit gases are cooled and then expanded in a turbine to further reduce the temperature of the working fluid. The lower-temperature fluid is used to produce the refrigeration effect.
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| Heat-driven systems | are refrigeration systems whose energy input is based on heat transfer from an external source. Absorption refrigeration systems are often classified as heat-driven systems.
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| Heat pump | is a cyclic device which causes the transfer of heat from a low-temperature region to a high-temperature region. The objective of a heat pump is to maintain the heated space at a high temperature by supplying heat to it.
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| Ideal vapor-compression refrigeration cycle | completely vaporizes the refrigerant before it is compressed and expands the refrigerant with a throttling device, such as an expansion valve or capillary tube. The vapor-compression refrigeration cycle is the most widely used cycle for refrigerators, air-conditioning systems, and heat pumps. It consists of four processes: - 1-2 Isentropic compression in a compressor
- 2-3 Constant-pressure heat rejection in a condenser
- 3-4 Throttling in an expansion device
- 4-1 Constant-pressure heat absorption in an evaporator.
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| Multistage compression refrigeration system | is a cascade refrigeration system where the fluid used throughout the cascade refrigeration system is the same, and the heat exchanger between the stages is replaced by a device that has better heat-transfer characteristics, a mixing chamber (called a flash chamber).
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| Peltier effect | is the cooling effect that occurs when a small current passes through the junction of two dissimilar wires. This effect forms the basis for thermoelectric refrigeration and is named in honor of Jean Charles Athanase Peltier, who discovered this phenomenon in 1834.
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| Refrigerants | are the working fluids used in the refrigeration cycles.
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| Refrigerator | is a cyclic device which causes the transfer of heat from a low-temperature region to a high-temperature region. The objective of a refrigerator is to maintain the refrigerated space at a low temperature by removing heat from it.
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| Reversed Carnot cycle | is a reversible cycle in which all four processes that comprise the Carnot cycle are reversed during operation. Reversing the cycle will also reverse the directions of any heat and work interactions. The result is a cycle that operates in the counterclockwise direction.
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| Seebeck effect | results when two wires made from different metals are joined at both ends (junctions), form a closed circuit, and one of the ends is heated. As a result of the applied heat a current flows continuously in the circuit. The Seebeck effect is named in honor of Thomas Seebeck, who made its discovery in 1821.
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| Thermoelectric circuit | is a circuit that incorporates both thermal and electrical effects.
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| Thermoelectric generator | uses the Seebeck effect as the basis for thermoelectric power generation.
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| Thermoelectric refrigerator | is a refrigerator using electric energy to directly produce cooling without involving any refrigerants and moving parts.
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| Ton of refrigeration | is the capacity of a refrigeration system equivalent to the energy that can freeze 1 ton (2000 lbm) of liquid water at 0°C (32°F) into ice at 0°C in 24 h. One ton of refrigeration is equivalent to 211 kJ/min or 200 Btu/min. The cooling load of a typical 200-m2 (2153-ft2) residence is in the 3-ton (10-kW) range.
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