Flow boiling of R245fa in a single circular microchannel

Abstract

The present paper describes an experimental setup for the investigation of two-phase heat transfer inside microchannels and reports local heat transfer coefficients measured during flow boiling of HFC-245fa in a 0.96 mm diameter single circular channel. The test runs have been performed during vapourization at around 1.85 bar, corresponding to 31 oC saturation temperature. As a peculiar characteristic of the present technique, the heat transfer coefficient is not measured by imposing the heat flux; instead, the boiling process is governedby controlling the inlet temperature of the heating secondary fluid. In the data, mass velocity ranges between 200 and 400 kg/m2s, with heat flux ranging between 5 and 85 kW/m2 and vapor quality from 0.05 up to 0.8. Since these data are not measured at uniform heat flux conditions, a proper analysis is performed to enlighten the influence of the different parameters and to compare the present data to those increasing the water-to-refrigerant temperature difference and by decreasing it. Finally, the experimental data are compared to models available in the literature for prediction of the heat transfer coefficients inside microchannels.