Thermodynamic Analysis of Transcritical CO2 Ejector Expansion Refrigeration Cycle with Dedicated Mechanical Subcooling

Fu Fu,Liu Liu,Li Li,Yu Yu,Wang Wang,Zheng Zheng

doi:10.3390/e21090874

Abstract

The new configuration of a transcritical CO2 ejector expansion refrigeration cycle combined with a dedicated mechanical subcooling cycle (EMS) is proposed. Three mass ratios of R32/R1234ze(Z) (0.4/0.6, 0.6/0.4, and 0.8/0.2) were selected as the refrigerants of the mechanical subcooling cycle (MS) to further explore the possibility of improving the EMS cycle’s performance. The thermodynamic performances of the new cycle were evaluated using energetic and exergetic methods and compared with those of the transcritical CO2 ejector expansion cycle integrated with a thermoelectric subcooling system (ETS). The results showed that the proposed cycle presents significant advantages over the ETS cycle in terms of the ejector performance and the system energetic and exergetic performances. Taking the EMS cycle using R32/R1234ze(Z) (0.6/0.4) as the MS refrigerant as an example, the improvements in the coefficient of performance and system exergy efficiency were able to reach up to 10.27% and 15.56%, respectively, at an environmental temperature of 35 °C and evaporation temperature of −5 °C. Additionally, the advantages of the EMS cycle were more pronounced at higher environmental temperatures.

Highlights

The critical impact of the refrigeration and air-conditioning industry on ozone depletion and global warming has developed into an alarming issue, which is mainly attributed to the wide application of synthetic refrigerants
The results revealed that there were optimal design parameters in each test and the coefficient of performance (COP) of the cycle using an ejector was increased by 15% relative to the conventional cycle
Showed a similar pattern, which is consistent with c and the effect of the subcooling degree on COP

Summary

Introduction

The critical impact of the refrigeration and air-conditioning industry on ozone depletion and global warming has developed into an alarming issue, which is mainly attributed to the wide application of synthetic refrigerants. Interest in natural refrigerants have been increasing rapidly. A transcritical cycle mode is generally required at common refrigeration conditions because of the lower critical temperature of CO2 , which leads to great throttling loss [4]. The coefficient of performance (COP) of a transcritical CO2 system is often lower than that of a system using synthetic refrigerants. The COP drops rapidly as environmental temperature rises, which further limits the application of the cycle in warm and hot regions [5]. In order to improve system performance, some strategies have been adopted such as employing an expansion device to replace the throttling valve and installing a subcooling system behind the gas cooler

Methods

Results

Conclusion