An experimental study of flow boiling heat transfer and pressure drop of hydrofluoroolefin and hydrocarbon mixtures in a plate heat exchanger

Zeotropic mixture flow boiling in plate heat exchangers is an important heat transfer process that is relevant for a wide range of applications including organic Rankine cycle and heat pump systems, however, the basic theories of the governing heat transfer mechanisms remain poorly understood. This paper presents an experimental investigation of zeotropic mixture flow boiling in a plate heat exchanger, contributing to the state-of-the-art by providing an analysis of the heat transfer and pressure drop characteristics of different types of zeotropic mixtures, the heat transfer degradation of the mixtures, and the influential parameters on heat transfer degradation, as well as an evaluation of the applicability of the current heat transfer and pressure drop predictions methods. For this purpose, two types of zeotropic mixtures, R1234ze(E)/R1233zd(E) and propane/isobutene, were tested at three reduced pressures of 0.45, 0.55 and 0.65, corresponding to the bubble point temperature ranging from 61 °C to 131 °C. The heat flux was varied from 14.2 kW/m² to 37.6 kW/m² and mass flux ranged from 52 kg/m²s to 137 kg/m²s. The results indicate that there is a similarity of the heat transfer characteristics between the mixtures and their pure-component fluids, while the two types of mixtures show different heat transfer characteristics due to the differences in their thermo-physical properties. Moreover, the results suggest that the heat transfer degradation of the mixtures with respect to their pure-component fluids can go up to 34 %, with the degradation being largest for working conditions corresponding to weaker heat transfer performance. The evaluated prediction methods are able to provide the good predictions for the zeotropic mixtures, with mean absolute percentage deviations of 9.3 %–11.7 % for the flow boiling heat transfer coefficient predicted by the three prediction methods and a mean absolute percentage deviation of 8.6 % for frictional pressure drop.