Refrigeration Cycles
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Refrigeration CyclesRefrigeration Cycles
Power UsersPower Users
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Refrigerators and Heat PumpsRefrigerators and Heat Pumps
Refrigerators: Refrigerators: move heat move heat fromfrom colder spacecolder space
Heat pump: move Heat pump: move heat heat toto warmer warmer spacespace
Both require work Both require work inputinput
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Refrigerators and Heat PumpsRefrigerators and Heat Pumps
Performance is Performance is expressed in term expressed in term of coefficients of of coefficients of performanceperformance
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Carnot Cycle ModelCarnot Cycle Model
Reverse Carnot CycleReverse Carnot Cycle
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Reverse Carnot CycleReverse Carnot Cycle
Coefficients of performance for Coefficients of performance for Carnot cycles can be expressed in Carnot cycles can be expressed in terms of temperature terms of temperature
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Ideal Vapor-Compression Ideal Vapor-Compression Refrigeration CycleRefrigeration Cycle
1-2 Isentropic 1-2 Isentropic compression in compression in compressorcompressor
2-3 Constant-pressure 2-3 Constant-pressure heat rejection in a heat rejection in a condensercondenser
3-4 Throttling in an 3-4 Throttling in an expansion valve expansion valve (irreversible process)(irreversible process)
4-1 Constant-pressure 4-1 Constant-pressure heat absorption in an heat absorption in an evaporatorevaporator
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Ideal Vapor-Compression Ideal Vapor-Compression Refrigeration Cycle AnalysisRefrigeration Cycle Analysis
Steady-flowSteady-flow
Where hWhere h11 = h = hg@Pg@P11 and h and h33 = h = hf@Pf@P33
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Actual Vapor-Compression CycleActual Vapor-Compression Cycle
DifferencesDifferences Evaporator Evaporator
dischargedischarge Higher specific Higher specific
volume in volume in compressorcompressor
Compressor lossesCompressor losses Condenser pressure Condenser pressure
losseslosses
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What Refrigerant?What Refrigerant?
Types:Types: Chlorofluorocarbons (CFCs)Chlorofluorocarbons (CFCs) AmmoniaAmmonia Hydrocarbons (propane, ethane, Hydrocarbons (propane, ethane,
ethylene, etc.)ethylene, etc.) Carbon dioxideCarbon dioxide
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What Refrigerant?What Refrigerant?
Driving criteria:Driving criteria: TemperaturesTemperatures of of
where heat is where heat is removed removed fromfrom and and where it is moved where it is moved toto..
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Heat PumpsHeat Pumps
Reverse of Reverse of refrigeratorsrefrigerators
Bring heat from Bring heat from lower temperature lower temperature space to higher space to higher temperature space.temperature space.
Energy sourceEnergy source AirAir Water/soilWater/soil
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Gas Refrigeration CycleGas Refrigeration Cycle
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Gas Refrigeration CycleGas Refrigeration Cycle
Fluid always a gas, no phase changeFluid always a gas, no phase change
Lower COP than vapor-compression Lower COP than vapor-compression systemssystems
Used in aircraft and gas liquefactionUsed in aircraft and gas liquefaction
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