Vapor-liquid equilibrium measurement and heating performance modeling on eco-friendly zeotropic blends of CO2/R1234ze(Z) and CO2/R1336mzz(E)

In the context of sustainable development, CO2 and hydrofluoroolefins (HFOs) are regarded as promising refrigerant candidates. Despite recognition of application potential, the knowledge of their blends is insufficient. In this paper, vapor-liquid equilibrium (VLE) properties of two eco-friendly zeotropic CO2/HFO blends, namely CO2/R1234ze(Z) and CO2/R1336mzz(E), were measured at temperature from 253.15 K to 333.15 K at CO2 concentration from 0 to 1. Peng-Robinson (PR) model and Soave-Redlich-Kwong (SRK) model are identified as suitable models for describing VLE of CO2/HFO with deviation less than 4.5%, whereas Perturbed-Chain Sta-tistical Associating Fluid Theory (PC-SAFT) model is shown to have larger deviation. Furthermore, a heat pump water heater is modelled to demonstrate the working potential of CO2/HFO in terms of thermodynamics and safety, while the newly fitted binary interaction parameter kij being used. Both CO2/R1234ze(Z) and CO2/ R1336mzz(E) show more than 150% advantage in volumetric heating capacity and comparable heating effi-ciency compared to R134a. The optimal concentration of CO2 is higher than 0.6, eliminating the flammability of mixture. Additionally, the operating pressures of CO2/HFO are reduced to lower than 3.2 MPa at typical working condition due to HFO addition. The results contribute to the accurate VLE description of CO2/HFO and further investigation on the applications of eco-friendly refrigerants.

Automated summary

In this study, the vapor-liquid equilibrium properties of two eco-friendly CO2/HFO blends were measured and the Peng-Robinson and Soave-Redlich-Kwong models were found to accurately describe the VLE with deviations less than 4.5%. A heat pump water heater was also modeled to demonstrate the thermodynamic and safety advantages of CO2/HFO, showing higher volumetric heating capacity and comparable efficiency compared to R134a.