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Supercritical heat transfer has already been studied extensively, however, the majority of these studies focused on water or CO2. Data on refrigerants, which are used in for example transcritical or supercritical organic Rankine cycles or heat pumps, is scarce. Nonetheless, this data is crucial in order to size the heat exchangers used in these systems without significant overdimensioning. Therefore it is necessary to gain insight into the complex nature of supercritical heat transfer. For that purpose, experimental data on supercritical heat transfer to the refrigerant R125 is discussed in this work. Measurements were performed on a previously built test rig, where the refrigerant flowed in a horizontal tube with an inner diameter of 24.77 mm. Pressure, mass flux and heat flux were varied, and their influence on supercritical heat transfer was investigated. In general, heat transfer is enhanced for an increase in mass flux or decrease in heat flux, and no distinct effect of pressure on the heat transfer is measured.

A symmetrical distribution of the two-phase refrigerant mixture before the evaporator is crucial to achieve optimal performance of heat pumps. In a previous study experiments on two-phase flow in a horizontal symmetric impacting T-junction were conducted in our lab. The measurements performed include both pressure drop and phase distribution data of refrigerants. This data is unique as almost all previous experiments in literature investigate air-water flows. With this data a mechanistic model was constructed which is capable of predicting the phase distributions and pressure drop depending on the flow regime and the fluid properties. The model is capable of predicting 90% of the data with a maximum mean deviation of 5%.