Experimental Study of Effects of Volumetric Porosity and Critical Meniscus Radius on Evaporation/Boiling From Thin Capillary Wicks

Abstract

The evaporation/boiling heat transfer and critical heat flux (CHF) from surfaces coated with multiple, uniform layers of sintered isotropic copper mesh were studied experimentally in an atmospheric environment. Two series of investigations were conducted: one was designed to study the effects of the critical meniscus radius and effective pore size, which are controlled by the wire diameter and mesh number, with the volumetric porosity and wick thickness are held constant; and a second to study the effects of volumetric porosity for a constant wick thickness and effective pore size. The experimental results indicate that the critical heat flux (CHF) was strongly dependent on the critical meniscus radius and effective pore size, as well as the volumetric porosity; while the evaporation/boiling heat transfer coefficient was significantly affected by critical meniscus radius and effective pore size, but not strongly dependent on the volumetric porosity. The data further illustrate that the menisci at CHF are located in the corner formed by wire and heated wall and between the wires in both the vertical and horizontal directions. The minimum value of these three menisci determined the maximum capillary pressure generated through the capillary wick. Sample structure and fabrication processes as well as the test procedures, are described in detail and discussed. The experimental results and observations are systematically presented and analyzed.