Role of receiver on the performance of a transcritical CO2 based air-conditioning unit with single-stage and two-stage expansion

Mihir Mouchum Hazarika,Maddali Ramgopal,Souvik Bhattacharyya,Rodrigo Llopis Doménech

doi:10.1080/23744731.2021.1902189

Abstract

Theoretical and experimental studies are carried out on a transcritical CO2 based air-conditioning unit. Two configurations– a system with single-stage expansion (SSE) and a system with two-stage expansion (TSE) have been considered. Detailed numerical models have been developed for both configurations. Results obtained from numerical simulations are compared with experimental results. The performance of the system with single-stage expansion is compared with two-stage expansion under different conditions of refrigerant charge, receiver volume, and ambient temperature. Both numerical and experimental results show that the SSE configuration is highly sensitive to refrigerant charge as compared to the TSE configuration. The TSE configuration offers better system controllability provided the receiver is sized properly. Besides, it is found that for the same performance, the required charge can be reduced by about 15% for the TSE configuration as compared to the SSE configuration.

Highlights

With the rising concerns about global warming, the use of harmful synthetic refrigerants with high global warming potential (GWP) is no longer encouraged
The performance of the system with single-stage expansion is compared with two-stage expansion under different conditions of refrigerant charge, receiver volume, and ambient temperature
Two configurations are considered for the present system—one with single-stage expansion and the other with two-stage expansion

Summary

Introduction

With the rising concerns about global warming, the use of harmful synthetic refrigerants with high global warming potential (GWP) is no longer encouraged. Environment-friendly, natural refrigerants are seen as permanent replacements for the high GWP, synthetic refrigerants. Hydrocarbons have been widely used in recent years for small capacity refrigeration and air-conditioning applications. Though ammonia is an excellent refrigerant and is widely used, it is toxic and suffers from material compatibility issues. Carbon dioxide (CO2), being non-flammable as well as nontoxic, is considered as a promising natural refrigerant due to its excellent thermophysical properties and material compatibility.

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Conclusion