Evaporation of R1234yf, R1234ze(E) and R1234ze(Z) on Cu surface: A molecular dynamics study

Abstract

Understanding the interface phase transition behavior of the working fluid helps to improve the energy conversion efficiency of a thermodynamic cycle. In this study, the evaporation behaviors of R1234yf, R1234ze(E) and R1234ze(Z) liquid film on the solid surface are performed using molecular dynamics simulation. The results suggest the evaporation rate and heat flux almost remain constant in the steady state. And during this period, the evaporation rate and heat flux of R1234yf is the largest among the studied systems. Meanwhile, the total thermal resistance of R1234ze(Z) system is greater than that of R1234ze(E) and R1234yf. The Kapitza resistance between solid and liquid accounts for only a small part of the total thermal resistance. The main reason for the difference of the total thermal resistance is the large difference of evaporation resistance at the liquid–vapor interface. Furthermore, the largest liquid–vapor interface area gives R1234yf the largest surface area for heat and mass transfer, thus enhancing the performance of evaporation. Besides, R1234yf has the smallest surface tension, followed by R1234ze(E) and R1234ze(Z). And the self-diffusion coefficient of R1234yf is the greatest. R1234yf also has the smallest interaction energy between liquid molecules. Therefore, the R1234yf liquid molecule is easy to escape from the liquid–vapor interface among the studied systems.