THE SECOND THERMODYNAMICS LAW DETERMINES THE OPTIMAL INTERMEDIATE PRESSURE OF TWO-STAGE REFRIGERATION CYCLE

George K Alexis, Antonis G Nazos

Abstract


A two-stage vapor compression refrigeration system using R22, R717, R134a and R143a as refrigerants is thermodynamically analyzed in the present work in order to determine the optimal intermediate pressure. Various design parameters that will maximize the coefficient of performance COP and the efficiency of second thermodynamic law ε are considered as given. More specifically, the design conditions are: condenser temperature 25-45oC and evaporator temperature -50-0oC. At the maximum efficiency of the second thermodynamic law corresponds the optimal intermediate pressure which depends on the used refrigerant. The investigation shows that the optimal operation of the cycle is close to the geometric mean of the evaporation and the condensation pressures. In every case the maximum exergy destruction takes place in condenser.


Keywords


Two-stage refrigeration cycle, refrigerant, exergy, second thermodynamic law analysis, COP

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