The experimental investigation of the vapor-liquid-liquid and solid-liquid phase equilibrium for (difluoromethane + octafluoropropane) mixture

Abstract

In this work, the solid-liquid equilibrium (SLE) and vapor-liquid-liquid equilibrium (VLLE) were studied in a cryogenic mixture of difluoromethane (R32) + octafluoropropane (R218). The SLE was measured by a calorimetric method, while the VLLE was measured by a vapor-phase recirculation method for this binary mixture at temperatures ranging from 203.150 to 237.151 K. This binary mixture does not show the common eutectic behavior, and the temperatures of the liquidus line were invariable at different mole fraction. The experimental VLLE data was analyzed by the polynomial and the rectilinear diameter methods to obtain the second liquid phase compositions coexisting in equilibrium. Both methods show good agreement with the experimental data. The liquid phase split was observed below the upper critical end point (UCEP), which is 237.791 K based on the polynomial methods. Beside, a solid-liquid-liquid equilibrium (SLLE) of R32 + R218 was inferred based on the experimental data, which is utilized to explain the unusual experimental data in mixed refrigerants.