Cycle Performance and Heat Transfer Characteristics of a Heat Pump Using R22/R142b Refrigerant Mixtures

A heat pump system is constructed tO evaluate the performance and the heat transfer characteristics. Mixtures of R22/Rl42b are adopted in the heat pump. The heat transfer in the evaporator and the overall perfomance arc measured and analyzed in terms of the compositions and the flow rate of the refrigerants. The evaporator consists of counter~currem concentric circular tubes. Possibility of capacity modulation by changing composition is observed without degradation of heat transfer coefficients and coefficem of performance for a fixed volumetric displacement rate. The evaporating capacuy may be varied continuously within 200 percent based on minimum capacity. For similar cooling load, COP is improved by mixing two refrigerants and shows maximum value at 60% mass fraction of R22. Local heat transfer coefficients are obtained in the evaporator and shown as a function of composition for given values of mass flow rate. Heat transfer coefficients of mixtures are decreased in comparison with pure refrigerants at similar mass flow rate and average evaporating temperature.