Thermodynamic Calculations of Two-Stage Vapor Compression Refrigeration Cycle with Flash Chamber and Separate Vapor Mixing Intercooler

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1 Thermodynamic Calculations of Two-Stage Vapor Compression Refrigeration Cycle with Flash Chamber and Separate Vapor Mixing Intercooler Author: Volodymyr Voloshchuk Introduction In the event that a high COP of a refrigeration cycle is of greater importance compared to other factors, it is possible to significantly increase the COP of a basic cycle through the use of a multistage vapor compression cycle. This is especially true when the pressure ratio between the heat rejection and heat absorption pressures is large 5 or more. Multistaging involves one or more intermediate pressures between the heat rejection and heat absorption pressures, and a series of compressors operating between successive pressure intervals. One type of multi-compressor vapor compression cycle includes a mixing chamber where saturated vapor from the flash chamber mixes with the vapor leaving the low pressure stage compressor. This vapor-mixing chamber acts as a regenerative intercooler since it cools the superheated vapor leaving the low-pressure stage compressor using lower temperature saturated workin fluid, mixing the two prior to the next stage of compression. This type of refrigeration cycle is analysed in the following calculation.

2 Creation functions on properties and processes of working fluids Vapor pressure on the saturated line as a function of temperature Liquid pressure on the saturated line as a function of temperature Liquid temperature on the saturated line as a function of pressure Vapor temperature on the saturated line as a function of pressure Liquid specific enthalpy on the saturated line as a function of temperature Vapor specific enthalpy on the saturated line as a function of temperature Liquid specific enthalpy on the saturated line as a function of pressure

3 Vapor specific enthalpy on the saturated line as a function of pressure Liquid specific entropy on the saturated line as a function of temperature Vapor specific entropy on the saturated line as a function of temperature Liquid specific entropy on the saturated line as a function of pressure Vapor specific entropy on the saturated line as a function of pressure Temperature as a function of pressure and specific entropy Temperature as a function of pressure and specific enthalpy Specific enthalpy as a function of pressure and temperature Specific entropy as a function of pressure and temperature Input Data Temperature of heat source Temperature of heat consumption Temperature difference in the evaporator (3.1) (3.2)

4 Temperature difference in the condenser Isentropic efficiency of the compressor Pressure increase in compressor 1 Working fluid (3.3) (3.4) (3.5) (3.6) (3.7) Calculations Temperature of the working fluid at the evaporator outlet Pressure of the working fluid at the evaporator outlet Specific enthalpy of the working fluid at the evaporator outlet (4.1) (4.2) (4.3) Specific entropy of the working fluid at the evaporator outlet (4.4) Pressure of the working fluid at the flash intercooler outlet Pressure of the working fluid at the flash intercooler outlet Temperature of the working fluid at the flash intercooler outlet Specific enthalpy of the working fluid at the flash intercooler outlet (4.5) (4.6) (4.7)

5 (4.8) Specific enthalpy of the working fluid at the flash intercooler outlet (4.9) Pressure of the working fluid at the evaporator intlet Specific enthalpy of the working fluid at the evaporator intlet (4.10) (4.11) Temperature of the working fluid at the evaporator intlet Specific enthalpy of saturated liquid of the working fluid at the evaporator inlet (4.12) (4.13) Quality of the working fluid at the evaporator intlet Specific entropy of saturated liquid of the working fluid at the evaporator inlet (4.14) (4.15) Specific entropy of the working fluid at the evaporator inlet (4.16) Specific entropy of the working fluid at the compressor 1 outlet after isentropic compression (4.17) Temperature of the working fluid at the compressor 1 outlet after isentropic compression Specific enthalpy of the working fluid at the compressor 1 outlet after isentropic compression (4.18)

6 (4.19) Enhtalpy change in the compressor after isentropic compression (4.20) Enhtalpy change in the compressor 1 after actual compression (4.21) Specific enthalpy of the working fluid at the compressor 1 outlet after actual compression (4.22) Specific enthalpy of the working fluid at the compressor 1 outlet after actual compression Specific entropy of the working fluid at the compressor 1 outlet after actual compression (4.23) (4.24) Pressure of the working fluid at the vapor mixing intercooler inlet Temperature of the working fluid at the vapor mixing intercooler inlet Specific enthalpy of the working fluid at the vapor mixing intercooler inlet (4.25) (4.26) (4.27) Specific entropy of the working fluid at the vapor mixing intercooler inlet (4.28) Temperature of the working fluid at the condenser outlet Pressure of the working fluid at the condenser outlet (4.29) (4.30)

7 Specific enthalpy of the working fluid at the condenser outlet (4.31) Specific entropy of the working fluid at the condenser outlet (4.32) Pressure of the working fluid at the compressor 2 outlet Pressure of the working fluid at the compressor 2 inlet Pressure increase in the compressor 2 (4.33) (4.34) Specific enthalpy of the working fluid at the flash chamber intlet (4.35) (4.36) Pressure of the working fluid at the flash chamber intlet Temperature of the working fluid at the flash chamber intlet Specific enthalpy of saturated liquid of the working fluid at the flash chamber inlet (4.37) (4.38) (4.39) Specific enthalpy of saturated vapor of the working fluid at the flash chamber inlet (4.40) Quality of the working fluid at the flash chamber intlet Specific entropy of saturated liquid of the working fluid at the flash chamber inlet (4.41)

8 (4.42) Specific entropy of saturated liquid of the working fluid at the flash chamber inlet (4.43) Specific entropy of the working fluid at the flash chamber inlet (4.44) Ratio of mass flow rates between the high pressure circuit and that of the low pressure circuit Specific enthalpy of the working fluid at the compressor 2 intlet (4.45) (4.46) Temperature of the working fluid at the compressor 2 intlet Specific entropy of the working fluid at the compressor 2 intlet (4.47) (4.48) Specific entropy of the working fluid at the compressor 2 outlet after isentropic compression (4.49) Temperature of the working fluid at the compressor 2 outlet after isentropic compression Specific enthalpy of the working fluid at the compressor 2 outlet after isentropic compression (4.50) (4.51) Enhtalpy change in the compressor 2 after isentropic compression (4.52) Enhtalpy change in the compressor 2 after actual compression

9 (4.53) Specific enthalpy of the working fluid at the compressor 2 outlet after actual compression (4.54) Specific enthalpy of the working fluid at the compressor 2 outlet after actual compression Specific entropy of the working fluid at the compressor 2 outlet after actual compression (4.55) (4.56) Heat rejection in the condenser referred to 1 kg of refrigerant in the low pressure circuit (4.57) Heat addition in the evaporator referred to 1 kg of refrigerant in the low pressure circuit (4.58) The total work of compressors referred to 1 kg of the working fluid in the low pressure circuit (4.59) Coefficent of performance of a refrigerator Coefficent of performance of a heat pump (4.60) (4.61) Plot the Refrigeration Cycle on a P-h-T Chart

Week 9. Refrigeration Cycles I. GENESYS Laboratory

Week 9. Refrigeration Cycles I Objectives 1. Introduce the concepts of refrigerators and heat pumps and the measure of their performance. 2. Analyze the ideal vapor-compression refrigeration cycle. 3.