Experimental evaluation of the CO2-based mixtures CO2/R32, CO2/R1234yf and CO2/R1270 in a transcritical refrigerating plant considering the effect of the internal heat exchanger (IHX)

Abstract

Using CO2 mixtures results in a simple but effective solution to increase the critical temperature of CO2 and reduce its working pressures. However, the overall effect of these mixtures on the global performance of the cycle has yet to be explored experimentally in detail. Accordingly, this work tests three CO2-binary blends with R32, R1270 and R1234yf in a small-capacity vapour compression test rig considering the same working conditions of heat rejection temperature and cooling demand. These mixtures were compared with pure CO2 in two-cycle arrangements without and with the internal heat exchanger (IHX). The results without IHX provided COP enhancements of 6.4%, 9.7% and 15.3% with CO2/R1270, CO2/R1234yf and CO2/R32, respectively, compared to CO2 without IHX. Using the IHX and taking CO2 without IHX as a reference, the COP increments ranged from 6.7% with R744, 12.1% with CO2/R1270, 16.1% with CO2/R1234yf and 22.2% with CO2/R32.