Mohamed Iqbal Pallipurath Refrigeration Cycles Mohamed Iqbal Pallipurath

Refrigerators and Heat Pumps 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

Carnot Cycle Model Reverse Carnot Cycle

Reverse Carnot Cycle Coefficients of performance for Carnot cycles can be expressed in terms of temperature

Ideal Vapor-Compression Refrigeration Cycle 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 Analysis Steady-flow Where h1 = hg@P1 and h3 = hf@P3

Actual Vapor-Compression Cycle Differences Evaporator discharge Higher specific volume in compressor Compressor losses Condenser pressure losses

What Refrigerant? Types: Chlorofluorocarbons (CFCs) Ammonia Hydrocarbons (propane, ethane, ethylene, etc.) Carbon dioxide

What Refrigerant? Driving criteria: Temperatures of where heat is removed from and where it is moved to.

Heat Pumps Reverse of refrigerators Bring heat from lower temperature space to higher temperature space. Energy source Air Water/soil

Gas Refrigeration Cycle

Gas Refrigeration Cycle Fluid always a gas, no phase change Lower COP than vapor-compression systems Used in aircraft and gas liquefaction