Calculating Circulation Concentration of Zeotropic Refrigerant Mixtures

The circulation concentration of a zeotropic refrigerant mixture may differ from the refrigerant bulk concentration in a vapor compression cycle. The difference, defined as "concentration shift," is mainly caused by the differential holdup in two-phase regions and the differential solubility of the oil. In this paper the concentration shift caused by the differential holdup of the two-phase flow of liquid and vapor in the condenser and evaporator were analyzed. Detailed models for calculating the circulation concentration were created. Based on the measurement results of an air-conditioning system, the proposed method was tested and proved to be satisfactory. It can be concluded that the principles of the proposed models are valid for any zeotropic refrigerant mixture in any refrigeration system.