Dryout Incipience and Critical Heat Flux in Saturated Flow Boiling of Refrigerants in a Vertical Uniformly Heated Microchannel

Abstract

The prediction of dryout occurrence is crucial in the design and safety of compact heat exchangers. For this purpose, a series of experimental tests have been performed to investigate dryout incipience and critical heat flux (CHF) in a circular vertical microchannel with internal diameter of 640 μm and a uniformly heated length of 213 mm using refrigerants R-134a, R-22 and R-245fa as working fluids. The effects of mass flux, system pressure, and refrigerant on the dryout heat flux and vapour quality are explored in detail. Finally, the experimental CHF results are compared to existing correlations both specially developed for microchannels and for macroscale geometries. The comparison shows good agreement with the classical Katto and Ohno (1984) correlation, developed for conventional large tubes. On the other hand, none of the microchannel correlations predicts in agreement the experimental data.