Analysis of R744 refrigeration system with liquid ejectors

Abstract

In recent years, there is a rapid increase in the cooling demand. Hence, not only the consumption of energy, but also the quantity of the refrigerants released into the air is increasing globally leading to planetary heating. Carbon dioxide (CO2, R744)is a natural refrigerant which is emerging as a potential replacement for HFCs and HCs nowadays because of its attractive properties. However, to avoid liquid entry into the compressor, conventional systems are designed and optimized to keep the exit part of the evaporator dry ensuring no liquid exits the evaporator. This requires superheating of the fluid which also contributes to internal irreversibility leading to lower COP. Hence, the liquid ejectors appeared as the potential option to improve the system COP, by facilitating complete use of the evaporator by avoiding superheating and securing a safe return of liquid refrigerant. This paper presents experimental results of a transcritical R744 system using a liquid ejector. Main aim of the present study is to use a liquid ejector to eliminate superheating of an evaporator and to made a comparison between its ON/OFF switching operation on the overall performance at high ambient temperature conditions (46°C) and its performance. It is observed that the increment in evaporator pressure and decrement in compressor power consumption are 4.5% and 5.5% respectively. Also, from the reduced superheat, it is evident that the proposed design can address the problem of uneven use of heat transfer area in the evaporator due to nonlinear refrigerant distribution and contribute to energy saving.