Cycle analysis and heat transfer characteristics of a heat pump using R22/R142b refrigerant mixtures

Abstract

A heat pump system is studied to evaluate its performance and heat transfer bharacteristics by adopting mixtures of R22/R142b as working fluids. Heat transfer coefficient in the evaporator and overall performance are measured and analysed in terms of compositions and relevant variables. The possibility is observed of capacity modulation within 200% (based on minimum capacity) by varying the composition without degradation of heat transfer effectiveness and coefficient of performance (COP). At a fixed evaporating capacity, COP is improved by using refrigerant mixtures, and shows its maximum at 60% mass fraction of R22. Local heat transfer coefficients are measured in the evaporator to identify the heat transfer characteristics. A similar mass flow rate and evaporating heat transfer rate, the average heat transfer coefficient for mixtures are lower than those for pure refrigerants. A cycle simulation taking the heat exchange process into consideration demonstrates the advantages of using refrigerant mixtures. Local heat transfer coefficientsduring evaporation are correlated with non-dimensional parameters, and reasonable agreement is obtained.