Optimized design of a heat exchanger for an air-to-water reversible heat pump working with propane (R290) as refrigerant: Modelling analysis and experimental observations

An experimental study of an air-to-water reversible heat pump unit was carried out using two different fin-and-tube heat exchanger “coil” designs and propane (R290) as the working fluid. The main aim of these tests was to search for optimized coil design concepts. The performance of the heat pump was evaluated for each coil design at different superheat conditions at the inlet of the compressor in both modes of operation: heating and cooling. Coefficient of Performance (COP) in both modes of each heat pump unit using two different coil design are presented. Experimental measurements are compared against model predictions. The mean refrigerant side heat transfer coefficient and the pressure drop as a function of mass flux along the flow path are calculated. As a results of tests, it was found that the performance was obtained in the heat pump unit using coil-2 design with less refrigerant circuit and a higher length of circuit with a superheat of around 6 K in both modes of operation. From the calculation it was found that in both modes of operation coil-2 design gives higher heat transfer coefficients and pressure drops for the refrigerant side.