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Refrigeration Cycles

Refrigeration Cycles. Power Users. 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.

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Refrigeration Cycles

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  1. Refrigeration Cycles Power Users

  2. Refrigerators: move heat from colder space Heat pump: move heat to warmer space Both require work input Refrigerators and Heat Pumps

  3. Performance is expressed in term of coefficients of performance Refrigerators and Heat Pumps

  4. Carnot Cycle Model • Reverse Carnot Cycle

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

  6. 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

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

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

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

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

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

  12. Gas Refrigeration Cycle

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

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