Research on Condensation Pressure and Temperature of Heat Pumps Using Blends of CO2 with Butane and Isobutane

Abstract

Based on the Thermodynamic theorem of corresponding states, the relationship between condensation pressure and temperature of subcritical heat pump systems using CO2/R600 or CO2/R600a as the working fluid is proposed. With the proposed correlation, the effective mass fraction range of component R600 or R600a can be readily determined according to the designed condensation pressure. Or if the condensation temperature is given, it is convenient to get the effective mass fraction scope of R600 or R600a. Within the condensation pressure range of 4.00–7.38 MPa, 36 points are calculated by the fitting formula and then checked by REFPROP8.0. The mean deviation between the fitting relationship and REFPROP8.0, below 1 %, shows that the proposed relationship can be used with satisfactory certainty under the given conditions. The research results may provide a beneficial basic data to promote the application of medium temperature heat pumps using blends of CO2 with butane and isobutane.