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Explore the principles of refrigeration cycles, including the Carnot Cycle Model, Vapor-Compression Cycle Analysis, and types of refrigerants. Learn about heat pumps, gas refrigeration cycles, and factors affecting system performance.
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Refrigeration Cycles Mohamed Iqbal Pallipurath
Refrigerators: move heat from colder space Heat pump: move heat to warmer space Both require work input Refrigerators and Heat Pumps
Performance is expressed in term of coefficients of performance Refrigerators and Heat Pumps
Carnot Cycle Model • Reverse Carnot Cycle
Reverse Carnot Cycle • Coefficients of performance for Carnot cycles can be expressed in terms of temperature
1-2 Isentropic compression in compressor 2-3 Constant-pressure heat rejection in a condenser 3-4 Throttling in an expansion valve (irreversible process) 4-1 Constant-pressure heat absorption in an evaporator Ideal Vapor-Compression Refrigeration Cycle
Ideal Vapor-Compression Refrigeration Cycle Analysis • Steady-flow • Where h1 = hg@P1 and h3 = hf@P3
Differences Evaporator discharge Higher specific volume in compressor Compressor losses Condenser pressure losses Actual Vapor-Compression Cycle
What Refrigerant? • Types: • Chlorofluorocarbons (CFCs) • Ammonia • Hydrocarbons (propane, ethane, ethylene, etc.) • Carbon dioxide
Driving criteria: Temperatures of where heat is removed from and where it is moved to. What Refrigerant?
Reverse of refrigerators Bring heat from lower temperature space to higher temperature space. Energy source Air Water/soil Heat Pumps
Gas Refrigeration Cycle • Fluid always a gas, no phase change • Lower COP than vapor-compression systems • Used in aircraft and gas liquefaction