Enhanced Saturation Boiling of HFE-7100 Dielectric Liquid on Extended Copper Surfaces

Experiments are performed, which investigated the enhancement in saturation boiling of HFE-7100 dielectric liquid on copper surfaces having a footprint of 10 × 10 mm and four 3 × 3 mm corner pins that are 2, 3 and 5 mm tall. These pins increase the geometrical surface area, by 96%, 144%, and 240%, respectively, and the surfaces are prepared using #400 and #1500 emery papers to investigate the effect of roughness on boiling heat transfer. Still photographs and video footage are recorded of the boiling processes. Nucleate boiling starts at a few isolated sites on the inside of the pins, close to the common line with the base surface, markedly reducing or eliminating the temperature excursion prior to boiling incipience. Measurable enhancements are obtained in both natural convection and nucleate boiling heat transfer. On the plane Cu surfaces prepared with emery paper #1500, the maximum nucleate boiling heat transfer coefficient, based on the foot print area, h_B^*, is 1.16 W/cm².K and increases to 1.80, 2.03 and 2.37 W/cm².K on the surfaces with 2, 3, and 5 mm tall pins. Similarly, the Critical Heat Flux (CHF), based on the foot print area, increases linearly with increased pin height, at a rate of ∼ 32% per mm. Increased surface roughness increases both h_B^* and CHF by additional 15% and 10% and markedly enhances nucleate boiling heat transfer at high surface superheats (ΔT_sat > ∼10 K), but causes only little enhancement at lower superheats.