Vapor-liquid equilibrium measurement and heating performance modeling on eco-friendly zeotropic blends of CO2/R1234ze(Z) and CO2/R1336mzz(E)
Jielin Luo, Zhiming Ye, Zhen Zhao, Kaiyin Yang, Shaozhi Zhang, Qin Wang
Abstract
In the context of sustainable development, CO 2 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 CO 2 /HFO blends, namely CO 2 /R1234ze(Z) and CO 2 /R1336mzz(E), were measured at temperature from 253.15 K to 333.15 K at CO 2 concentration from 0 to 1. Peng-Robinson (PR) model and Soave-Redlich-Kwong (SRK) model are identified as suitable models for describing VLE of CO 2 /HFO with deviation less than 4.5%, whereas Perturbed-Chain Statistical 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 CO 2 /HFO in terms of thermodynamics and safety, while the newly fitted binary interaction parameter k ij being used. Both CO 2 /R1234ze(Z) and CO 2 /R1336mzz(E) show more than 150% advantage in volumetric heating capacity and comparable heating efficiency compared to R134a. The optimal concentration of CO 2 is higher than 0.6, eliminating the flammability of mixture. Additionally, the operating pressures of CO 2 /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 CO 2 /HFO and further investigation on the applications of eco-friendly refrigerants.