Molecular dynamic simulation and SAFT modeling of the viscosity and self-diffusion coefficient of low global warming potential refrigerants

Abstract

Hydrofluoroolefins (HFOs) are among the recommended options to replace the currently used high global warming potential (GWP) hydrofluorocarbon (HFC) based refrigerants. The viscosity of both refrigerant classes was extensively measured in the literature. However, little to no information is available on the microscopic mobility of these molecules. In this work, the liquid densities (ρ), viscosities (η) and self-diffusion coefficients (D) of R-32, R-152a, R134a, R-1234yf, R-1234ze(E), R-1233zd(E), R-1224yd(Z) and R-1336mzz(Z) were predicted near saturation using molecular dynamic (MD) simulation. Data are reported across a wide range of conditions from 243 to 403 K. Results suggest a Stokes-Einstein type behavior that was exhibited by all refrigerants. Simulations also show that the DR-1234yf ≈ DR-152a, DR-1234ze(E) ≈ DR-134a and DR-1233zd(E) ≈ DR-1224yd(Z). The dynamic behavior of refrigerants is explained in relation to their molecular size, structure and interactions. Rosenfeld's entropy scaling was applied to correlate the viscosities and self-diffusion coefficients. Residual entropies were computed using the polar and perturbed chain form of the statistical associating fluid theory (Polar PC-SAFT).