Experimental Investigation of Boiling Heat Transfer in Freons Subjected to Forced Flow

Abstract

At the moment there exist no methods for computing the boiling heat transfer coefficient in a fluid flow that could take into account the diversity of flow modes for a wide range of flow parameters. The majority of experimental and analytical studies were performed at low reduced pressures. Noticeably fewer investigations were carried out at high reduced pressures. At present, there are numerous empirical heat transfer computation methods developed for various freons at moderate reduced pressures and mass velocities. There also exist dedicated formulas for computing heat transfer in mini- and microchannels, obtained at low reduced pressures. Power and refrigeration systems could be fitted with mini-channel heat exchangers with custom working fluids subjected to high or moderate pressures. It is necessary to verify whether the existing methods for computing heat transfer are valid at higher reduced pressures, up to pr ≈ 0.6, in a channel with a hydraulic diameter of d ≈ 1 mm. The paper presents an overview of existing methods for calculating the heat transfer coefficient in two-phase flows; we then generalise these and compare their results to our own experimental data. We obtained said experimental data at the reduced pressures of pr = p/pcr = 0.43 and 0.56 in the mass velocity range of G = 200--1500 kg/(m2 · s). The paper describes our test bench and the experimental procedure