Saturation Boiling of HFE-7100 Dielectric Liquid on Copper Surfaces with Corner Pins at Different Inclinations

Abstract

Results of experiments investigating saturation boiling of HFE-7100 dielectric liquid on 10 X 10 mm copper surfaces with 3× 3 mm corner pins, 2-, 3-, and 5-mm tall, are presented and discussed. Also investigated are the effects of surface roughness and inclination, from 0° (upward facing) to 180°, on the thermal power removed and the temperature of the footprint surface. Results are compared to those measured for a plane Cu surface of the same footprint area and surface roughness. New heat transfer results in natural convection and nucleate boiling and of Critical Heat Flux (CHF) at various orientations are obtained and a heat transfer correlation for natural convection is developed. The latter is important to the cooling of computer chips while in the standby mode of operation. In addition to reducing and/or eliminating the temperature excursion prior to boiling incipience, large enhancements in the heat removal rate are measured in both natural convection and nucleate boiling. In natural convection in the upward-facing orientation, the thermal power removed is ∼68% higher than from the plane Cu, at the same surface superheat, and independent of the surface roughness and the pin height. Consistent with the reported results by other investigators for macrostructured surfaces, the thermal power removed in nucleate boiling and at CHF increases as the wetted area by the boiling liquid increases, but the surface average heat fluxes decrease. Increasing the surface roughness increases the thermal power removed in nucleate boiling by 10−15%. For the surfaces with 2-, 3-, and 5-mm-tall pins at 0° inclination, the thermal powers removed at CHF of 40.5, 41.5, and 58.1 W represent increases of 79%, 83%, and 157%, compared to the plane Cu surface (22.6 W). CHF (46.5 W) for the surface with the 5-mm-tall pins at 180° inclination is as much as 83% of that at 0° (58.1 W), compared to only 20% for the plane Cu surface. The surface with the 5-mm tall corner pins also has the smallest boiling resistance, increasing from 0.43 K/W at 0° to 0.55 K/W at 180°, compared to 0.85 K/W and 2.8 K/W for plane Cu.