Zeotropic mixtures R1234ze(Z)/acetone and R1234ze(Z)/isohexane as refrigerants in high temperature heat pumps: Influence of the accuracy in thermodynamic properties evaluations

Abstract

High temperature heat pumps (HTHPs) represent an interesting option to upgrade waste heat up to 200 °C for industrial application. In order to achieve such high temperatures, suitable refrigerants are needed. In this paper, two zeotropic mixtures composed of a hydrofluoro-olefin (HFO) and a hydrocarbon, namely R1234ze(Z)/acetone and R1234ze(Z)/isohexane, were examined as the refrigerant for HTHP applications. The main objective of the present study is to determine the binary interaction parameters (BIPs) of the two zeotropic mixtures from experimentally-determined thermodynamic properties and analyze how HTHP performance assessment would change after tuning the BIPs. For R1234ze(Z)/acetone, after tuning the BIPs, the phase change temperature glide did not change that much. However, the composition corresponding to the highest temperature glide changed significantly. On the other hand, for R1234ze(Z)/isohexane, the phase change temperature glide changed significantly with tuned BIPs, while the composition for the maximum temperature glide was quite similar in the two cases. A thermodynamic optimization framework was used for simulation of the HTHP cycle. Simulation results using estimated BIPs showed that for R1234ze(Z)/acetone the optimum coefficient of performance (COP) was 3.95, while it slightly changed to 3.94 (around 0.25% change) after tuning the BIPs. However, the optimum composition of the mixture was quite different for the estimated and fitted BIPs. For R1234ze(Z)/isohexane the COP was 3.90 using estimated BIPs, while it changed to 3.83 (around 1.7% change) once the fitted BIPs were used. These results indicate the importance of tuning the BIPs for zeotropic mixtures and different impacts depending on the performance parameters analysed.