Experimental investigation on effects of surface texturing and surfactant on pool boiling performance of a vertically downward-faced copper surface

The orientation dependence of boiling surfaces poses a significant challenge to the heat transfer performance of two-phase thermal management systems working based on boiling heat transfer. Substantial reductions in performance were reported when the boiling surface is downward faced (at 180^⁰ orientation) compared to upward faced (0^⁰ orientation). The present study investigated the pool boiling performance of a downward-facing surface, incorporating surface modification via electrical discharge machining (EDM) and modification of the base working fluid, deionised (DI) water, by adding 10 % of the critical micelle concentration (CMC) of Dodecyl Trimethylammonium Bromide (DTAB), an ionic surfactant. The results demonstrated a significant enhancement in heat transfer coefficient in the margin of 50 % and a reduction in wall temperature in the range of 5.5 °C compared to the performance of a plain surface in DI water at a heat flux of 200 kW/m². The combined effect of surface modification and fluid modification on pool boiling heat transfer presented in this study effectively addresses the boiling instabilities, such as poor bubble dynamics and vapor bubbles hovering on boiling surfaces at lower heat fluxes encountered in downward-facing (adverse gravity conditions) surfaces.