Experimental assessment of CO2/R-152a mixtures in a refrigeration plant with integrated mechanical subcooling

Abstract

During the last years, CO2 utilization has grown in the refrigeration sector, especially in medium and large size plants. These cycles have implemented complex architectures to improve their energetic performance and be cost-effective. One of the most advanced architectures is cycle with the integrated mechanical subcooling. This work aims to experimentally evaluate the performance of this cycle using CO2/R-152a mixtures. Two R-152a mass concentrations, 5 % and 10 %, are selected for testing on a test rig at heat rejection temperatures from 20 °C to 40 °C with 5 °C step and at one temperature (2.50 °C of secondary fluid) at the inlet of the evaporator. The results show that the use of CO2/R-152a mixtures improves COP values of the cycle, confirming the trend observed in previous studies. However, it is observed that the cooling capacity decreases compared to pure CO2 due to the reduction in volumetric cooling capacity. The introduction of R-152a increases both critical temperature and pressure, and reduce the optimum heat rejection pressure, enabling more efficient operation in subcritical conditions. The study determines an upper limit for the R-152a mass fraction (10 %) beyond which the behaviour of the IMS cycle gets worse significantly compared to pure CO2.