THERMODYNAMIC ANALYSIS OF CO2/NH3 CASCADE REFRIGERATION SYSTEM

Abstract

This article presents an energy and exergy analysis of CO2/NH3 cascade refrigeration system.  CO2 refrigerant is used in low temperature cycle and NH3 refrigerant is used in high temperature cycle.  In present work, condensing and evaporating temperatures of NH3 in high temperature cycle is selected as 35°C and -10°C, while that of CO2 in low temperature cycle are 5°C and  -40° respectively.  Effect of temperature difference in cascade heat exchanger (CHE) on COP, second law efficiency, and exergy destruction rate is studied.  A complete mathematical model is prepared for the present work.  Calculated results show that maximum energy is found in condenser of high temperature cycle and minimum energy in the compressor of high temperature cycle while maximum exergy destruction rate is found in compressor of low temperature cycle and minimum exergy destruction rate in the expansion device of high temperature cycle.