Molecular modeling and simulation of vapor-liquid equilibrium of the refrigerant R152a and its mixture R152a + R32

A new all atom force field was developed for 1,1-difluoroethane (R152a) based on the Lennard-Jones (LJ) 12-6 plus point charge functional form. The parameters of two force fields with different initial charge configurations were derived from ab initio calculations and Monte Carlo simulations. Then both force fields were used to calculate phase equilibrium properties of R152a via Gibbs ensemble Monte Carlo simulations. The better model showed the mean unsigned deviations over the temperature range 250 < T (K) < 360 of 0.89%, 2.32%, and 2.84% in saturated liquid and vapor densities, and the vapor pressure, respectively. The calculated critical density, temperature, vapor pressure, normal boiling point, and heat of vaporization at 308.15 K also showed a good agreement with experimental data with deviations of 0.82%, 0.38%, 3.80%, 0.34%, 0.45%, respectively. This model was also used to predict the pressure-composition properties for the R152a + R32 mixture. In addition, molecular dynamics simulations were conducted to obtain the density, thermal expansivity, and transport properties of R152a in the temperature range from 278 to 308 K at pressures up to 1.5 MPa. Good agreement between the simulation results and experimental data and/or correlations (when available) validated the predictive ability of the proposed model.