Critical heat flux at high mass velocities in a microchannel and surface tension measurements for R514a

Abstract

This paper presents pioneer experimental data on critical heat flux (CHF) during flow boiling of low-pressure fluid R514a in a microchannel. The authors conducted experiments in a single smooth and horizontal microchannel, with an internal diameter of 1.1 mm and heating sections of 46 and 100 mm, a saturation temperature range of 56 to 122.7°C, and a mass velocity range of 1500 to 7500 kg/m2s. This research achieved high critical heat flux values, up to 1.85 MW/m2. The results were compared with the CHF of R123 under similar conditions and a higher CHF for R514a was observed. The performance of CHF predictive methods against the experimental data was performed. Since predictive methods for the CHF in microchannels need surface tension data, but there is a lack of experimental information about this property for R514a in the literature, this paper also presents experimental results for the surface tension of R514a and an expression for calculation of this property as a function of the temperature.