Effects of hole patterns on surface temperature distributions in pool boiling

Abstract

This paper presents the results of a study on critical heat flux (CHF) and boiling heat transfer (BHT) enhancements of a heating surface modified through the addition of holes of various dimensions. A layer of indium tin oxide was used as the heater material and holes of various patterns were incorporated onto the heating surfaces. The hole sizes and positions were controlled for precision using conventional microelectromechanical fabrication processes. Four types of heating surfaces were considered: (1) plain (i.e., no holes), (2) 9-hole, (3) 49-hole, and (4) 225-hole surfaces. For the 9 hole, 49 hole, and 225 hole patterned surfaces, and as compared to the plain heating surface, the CHF was enhanced by 16.7, 27.3, and 33.1%, respectively and heat transfer coefficients enhanced by 9.8, 26, and 26%, respectively. For the hole-patterned heating surfaces, distinct temperature distributions were observed consistently in the high heat flux regions - that is to say, the patterned areas exhibited lower temperature fields than the non-patterned areas. This indicates that heat was transferred more efficiently at the hole-patterned regions than at the neighboring non-patterned regions. The CHF and BHT performances were enhanced at the patterned surfaces because the high-temperature regions were well dispersed resulting in an increased effective heat transfer area. The CHF enhancement can be explained by the concept of the additional water supply on the heating surfaces.