Experimental investigation of flow boiling in single minichannels with low mass velocities

Abstract

Flow boiling characteristics in a single minichannel with the aspect ratio of 2 (1.8 mm width and 0.9 mm height) are studied experimentally. Experiments are conducted for different values of the wall heat flux (in the range of 204.7-431.3 kW/m(2)) and low mass fluxes (G = 20, 40 and 60 kg M-2 S-1) at a constant inlet temperature of deionized water (approximately 70 degrees C). Effects of the heat and mass fluxes on the local two phase heat transfer coefficient and the total pressure drop are examined. A considerable attention is also paid to performing high speed flow visualization study to have qualitative information about the flow physics. the heat transfer coefficient shows an irregular trend with increasing heat flux or the vapor quality, while it increases with increasing mass flux. on the other hand, the pressure drop increases with an increase in the heat flux or in the exit vapor quality. For the lowest mass flux value considered, temperature jump or the critical heat flux (CHF) condition is shown to occur at higher heating powers.