Experimental Investigation of Binary Mixture Flow Boiling in Micro-Channels

Abstract

An experimental study is performed to investigate flow boiling heat transfer characteristics of methanol-water mixtures in micro-channels. The test section contains 24 parallel channels having a 200 μm x 400 μm cross-section. Tests are conducted with pure water and methanol as well as five methanol-water binary mixtures with methanol molar fraction ranging from 18% to 76% over a mass velocity range of 275–868 kg/m2s and at an inlet temperature of Tin=Tbubble-20℃. The testing results show a number of intriguing characteristics of micro-scale mixture flow boiling. Both dissipative heat flux and micro-channel wall temperature at the onset of flow boiling in the micro-channels decreased with increasing methanol molar fraction. Flow boiling heat transfer coefficient decreased with increasing methanol molar fraction for a fixed vapor quality. Testing also showed two-phase pressure drop across the micro-channels increased appreciably once flow boiling occurred in micro-channels. Correlations used to predict the heat transfer coefficient and two-phase pressure drop in pure fluids were applied to the experimental results in this study to determine their predictive capabilities for two-component mixture fluids.