Effects of surface characteristics on flow boiling heat transfer

The present study focuses on examining the effect of surface characteristics on flow boiling heat transfer by obtaining experimental data for flow boiling of subcooled water over heater surfaces with different surface treatments. Four surfaces with average roughness values of 0.188, 0.363, 0.716 and 3.064 urn, and a commercially prepared sintered surface are employed in a flow boiling setup using water at atmospheric pressure. The apparatus consists of a 9.5 mm circular heater placed on the lower wall of a 3 mm x 40 mm horizontal channel. The results show that surface characteristics can influence heat transfer and are responsible for the scatter in flow boiling data. Cavity geometry seems to be a more important parameter. Only large differences in surface characteristics, such as a sintered surface, produce large increases in heat transfer. A microscope and an imaging software program are used to obtain the cavity distributions for each of the roughened surfaces. The cavity distributions on the surfaces are looked at in light of their experimentally determined heat transfer performance. The differences in the data sets for the four roughened surfaces are in the range of 0% to 28.8%. This comparable to the scatter observed in the flow boiling data from different investigators for experiments conducted under otherwise similar conditions. A discussion is then presented on the possible mechanisms responsible for the enhanced heat transfer due to surface characteristics