Prediction of isoenthalps, Joule–Thomson Coefficients and Joule–Thomson inversion curves of refrigerants by molecular simulation

We describe molecular simulation methodology based on the recently proposed NPH MC algorithm to calculate isoenthalps (HC), Joule–Thomson coefficients, μ  , (JTC) and Joule–Thomson inversion curves (JTIC), and apply it to the representative ethane-based alternative refrigerants R125, R134a and R152a over a wide range of thermodynamic conditions. Although JTIC have been calculated previously by molecular simulation, HC and JTC have rarely been studied by this approach, due to the requirement to incorporate ideal gas specific heat data, cpIG(T). Traditionally, calculations of HC, JTC and JTIC have been implemented using multi-parameter empirical equations fitted to experimental data. In contrast, molecular simulation methodology requires a force field (FF) describing the molecular interactions, which contains a relatively small number of adjustable parameters. Our study uses FFs from the literature, and cpIG(T) from a comprehensive compilation based solely on quantum and statistical mechanical calculations. Our simulation results are compared with pseudo-experimental results obtained from the REFPROP software package. We generated results in both single- and two-phase regions, and for thermodynamic conditions outside the range of REFPROP's capabilities. Where both sets of results are available, the simulation results are in good agreement with those of REFPROP. Our studies also suggest that more accurate quantum and statistical mechanical calculations of the refrigerant cpIG(T), which are feasible with current computer technology, would improve the reliability of both empirically based and molecular simulation calculations of HC and JTC for existing refrigerants, and would also reduce the experimental data requirement for newly proposed candidate refrigerants. Finally, we also compare our results with those from new calculations using two representative cubic equations of state (EOS); they provide reasonable but not quantitatively accurate results, particularly for μ and the JTIC.