Evaluating the use of CO2-Hydrocarbon blends as working fluids in high temperature heat pumps

Using natural substances in mixtures aims to develop an eco-friendly refrigerant that meets current greenhouse gas regulations and overcomes the in thermodynamic and safety drawbacks of individual refrigerants. A CO2/HCs mixture has the advantages of lowering operating pressures and increasing the critical temperature compared to pure CO2. The ability of the zeotropic mixture to increase performance through glide and reducing heat exchanger irreversibility is investigated. In addition, the resulting mixture is non toxic, has low global warming potential (GWP), avoids the impact of per- and polyfluoroalkyl substances (PFAs) and is low cost, making it a solution to the environmental damage caused by synthetic refrigerants. The aim of this work is to identify promising mixtures suitable for high temperature heat pump applications and to evaluate them under several operating conditions, with the ultimate goal of initiating experimental evaluations. A theoretical model, with CO2/R-290, CO2/R-600a and CO2/R-600 mixture properties simulated in REFPROP v10.0, is presented, and preliminary results are reported in this study.