Refrigeration cycle design for refrigerant mixtures by molecular simulation

Abstract

We describe a molecular simulation methodology to calculate the properties of a vapor-compression refrigeration cycle and its Coefficient of Performance, in the case when the refrigerant is a mixture. The methodology requires only a molecular force-field model for each refrigerant pure component and, for improved accuracy, an expression for the vapor pressure of each pure component as a function of temperature. Both may be constructed by means of theoretical approaches in combination with minimal amounts of experimental data, and the latter may also be estimated by empirical formulae with reasonable accuracy. The approach involves a combination of several available molecular-level computer simulation techniques for the individual processes of the cycle. This work extends our earlier study to cases when the refrigerant is a pure fluid. The mixture refrigerant simulations entail the calculation of bubble- and dew-point curves for the refrigerant mixtures, and we propose a new approach for dew-point calculations via molecular simulation. We compare results for a test case with those obtained from the Equation-of-State model used in the standard REFPROP software and with experimental data for a commercially available refrigerant mixture of R32 (CH2F2) and R143a (CH2FCF3).