Use of Liquid Film Evaporation in Biporous Media to Achieve High Heat Flux Over Large Areas

Abstract

Boiling characteristics of three biporous and one monoporous sintered wick are tested. The monoporous wick has the same wick thickness as a comparable biporous wick. Diameters of the clusters of the comparable biporous wick are equal to the powder diameter of the monoporous wick. A second biporous wick has the same configuration as the first, but is sintered in a thicker layer. The third biporous wick that is tested has smaller cluster sizes then the first two. All three biporous wicks have clusters sintered from powder with the same size distribution. The results demonstrate the advantages of a biporous capillary structure. All biporous wicks reached higher critical heat flux (CHF) then the monoporous wick. Experiments show that larger clusters are better than smaller. Comparing two different wick thicknesses, we can see that even though there is a dryout region inside the thick wick, it is still able to continuously remove heat at constant superheat. No sudden changes in superheat are seen. This process of heat removal is not possible with the thin wick. The working fluid in all runs is methanol. 4-mm thick wick with powder diameter ranging from 53 to 63 microns and cluster diameter ranging from 500 to 707microns is able to remove 377W/cm2 at temperature difference 110°C. A partial pressure inside the test chamber at this heat flux is 0.68atm and the interface temperature 167°C.