Miscibility Measurement and Evaluation for the Binary Refrigerant Mixture Isobutane (R600a) + 1,1,1,2,3,3,3-Heptafluoropropane (R227ea) with a Mineral Oil

Abstract

The miscibility of refrigerants with mineral oils is very important in the process of refrigerant substitution. The experimental critical solubility temperature (TCST) for the binary refrigerant mixture isobutane (R600a) + 1,1,1,2,3,3,3-heptafluoropropane (R227ea) in varying proportions with a 3GS (viscosity, ISO 32) naphthenic mineral oil was determined over a wide temperature range from 223.15 K to 303.15 K, and over an oil mass fraction range from 5 % to 20 %. A method based on analysis of the element type and number was proposed not only for evaluating the miscibility degree of pure refrigerants, but also for fitting miscibility data of the binary refrigerant mixture R600a/R227ea with the mineral oil. The miscibility evaluation result of R600a/R227ea with the mineral oil was calculated and shown on a triangular diagram which included five regions, standing for the area of TCST over 303.15 K, between 273.15 K and 303.15 K, between 253.15 K and 273.15 K, between 233.15 K and 253.15 K, and below 233.15 K, respectively. The diagram showed that when the mass fraction of R600a was below 20 % in the R600a/R227ea/mineral oil solution, a second liquid phase (oil-rich phase) would appear under common air-conditioning refrigeration temperatures; when the mass fraction of R600a was over 30 %, the liquid phase would not appear.