thermodynamic calculations of two-stage vapor compression
TRANSCRIPT
Thermodynamic Calculations of Two-StageVapor Compression Refrigeration Cycle
with Flash Chamber and Separate Vapor Mixing Intercooler
Author: Volodymyr Voloshchuk
IntroductionIn 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.
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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
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(3.1)(3.1)
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(3.2)(3.2)
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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 DataTemperature of heat source
Temperature of heat consumption
Temperature difference in the evaporator
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(3.5)(3.5)
(3.7)(3.7)
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(4.7)(4.7)
(4.4)(4.4)
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(3.3)(3.3)
(3.6)(3.6)
(4.3)(4.3)
(4.6)(4.6)
(3.4)(3.4)
(4.5)(4.5)
> > (4.1)(4.1)
(4.2)(4.2)
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Temperature difference in the condenser
Isentropic efficiency of the compressor
Pressure increase in compressor 1
Working fluid
CalculationsTemperature 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
Specific entropy of the working fluid at the evaporator outlet
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
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(4.14)(4.14)
(4.9)(4.9)
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(4.17)(4.17)
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(4.16)(4.16)
(4.19)(4.19)
(4.15)(4.15)
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(4.8)(4.8)
(3.3)(3.3)
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(4.10)(4.10)
(4.12)(4.12)
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(4.18)(4.18)
(4.11)(4.11)
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(4.13)(4.13)
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Specific enthalpy of the working fluid at the flash intercooler outlet
Pressure of the working fluid at the evaporator intlet
Specific enthalpy of the working fluid at the evaporator intlet
Temperature of the working fluid at the evaporator intlet
Specific enthalpy of saturated liquid of the working fluid at the evaporator inlet
Quality of the working fluid at the evaporator intlet
Specific entropy of saturated liquid of the working fluid at the evaporator inlet
Specific entropy of the working fluid at the evaporator inlet
Specific entropy of the working fluid at the compressor 1 outlet after isentropic compression
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
(4.27)(4.27)
(4.28)(4.28)
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(4.29)(4.29)
(4.22)(4.22)
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(4.19)(4.19)
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(4.8)(4.8)
(3.3)(3.3)
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(4.25)(4.25)
(4.30)(4.30)
(4.20)(4.20)
(4.21)(4.21)
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(4.24)(4.24)
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(4.23)(4.23)
(4.26)(4.26)
Enhtalpy change in the compressor after isentropic compression
Enhtalpy change in the compressor 1 after actual compression
Specific enthalpy of the working fluid at the compressor 1 outlet after actual compression
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
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
Specific entropy of the working fluid at the vapor mixing intercooler inlet
Temperature of the working fluid at the condenser outlet
Pressure of the working fluid at the condenser outlet
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(4.38)(4.38)
(4.40)(4.40)
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(4.37)(4.37)
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(4.32)(4.32)
(4.19)(4.19)
(4.41)(4.41)
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(4.33)(4.33)
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(4.36)(4.36)
(4.8)(4.8)
(4.39)(4.39)
(3.3)(3.3)
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(4.35)(4.35)
(4.31)(4.31)
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(4.34)(4.34)
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(4.42)(4.42)
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Specific enthalpy of the working fluid at the condenser outlet
Specific entropy of the working fluid at the condenser outlet
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
Specific enthalpy of the working fluid at the flash chamber intlet
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
Specific enthalpy of saturated vapor of the working fluid at the flash chamber inlet
Quality of the working fluid at the flash chamber intlet
Specific entropy of saturated liquid of the working fluid at the flash chamber inlet
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(4.50)(4.50)
(4.48)(4.48)
(4.43)(4.43)
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(4.49)(4.49)
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(4.19)(4.19)
(4.44)(4.44)
(4.51)(4.51)
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(4.8)(4.8)
(3.3)(3.3)
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(4.52)(4.52)
(4.45)(4.45)
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(4.42)(4.42)
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(4.46)(4.46)
(4.47)(4.47)
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Specific entropy of saturated liquid of the working fluid at the flash chamber inlet
Specific entropy of the working fluid at the flash chamber inlet
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
Temperature of the working fluid at the compressor 2 intlet
Specific entropy of the working fluid at the compressor 2 intlet
Specific entropy of the working fluid at the compressor 2 outlet after isentropic compression
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
Enhtalpy change in the compressor 2 after isentropic compression
Enhtalpy change in the compressor 2 after actual compression
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(4.54)(4.54)
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(4.19)(4.19)
(4.59)(4.59)
(4.58)(4.58)
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(4.53)(4.53)
(4.8)(4.8)
(3.3)(3.3)
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(4.61)(4.61)
(4.60)(4.60)
(4.56)(4.56)
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(4.57)(4.57)
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(4.42)(4.42)
(4.55)(4.55)
Specific enthalpy of the working fluid at the compressor 2 outlet after actual compression
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
Heat rejection in the condenser referred to 1 kg of refrigerant in the low pressure circuit
Heat addition in the evaporator referred to 1 kg of refrigerant in the low pressure circuit
The total work of compressors referred to 1 kg of the working fluid in the low pressure circuit
Coefficent of performance of a refrigerator
Coefficent of performance of a heat pump
Plot the Refrigeration Cycle on a P-h-T Chart
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(4.19)(4.19)
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(4.42)(4.42)
(4.53)(4.53)
(4.8)(4.8)
(3.3)(3.3)
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