Heat transfer charcacteristics in a copper micro-evaporator and flowpattern-based prediction method for flowboiling in microchannels

Abstract

This article presents new experimental results for two-phase flow boiling of R-134a, R-1234ze(E) and R-245fa in a micro-evaporator. The test section was made of copper and composed of 52 microchannels 163μm wide and 1560μm high with the channels separated by 178μm wide fins. The channels were 13.2mm long. There were 35 local heaters and temperature measurements arranged in a 5×7 array as a pseudo-CPU. The total pressure drops of the test section were below 20kPa in all cases. The wall heat transfer coefficients were generally above 10'000W/m2K and a function of the heat flux, vapor quality and mass flux. A new flow pattern-based prediction method for flow boiling heat transfer coefficients in microchannels was developed based on the experimental results. The new prediction method also predicted published data for four other test sections accurately, capturing the trends versus vapor quality well.