On the role of confinement plate wettability on pool boiling heat transfer

Abstract

Remarkably high heat transfer coefficient observed during boiling makes it one of the most sought-after thermal management solutions. However, the heat dissipation potential deteriorates in practical scenarios of confined spaces typically encountered in electronic packages and compact heat exchangers, among others. Contrary to unconfined pool boiling, confinement hinders buoyancy aided vapor removal from the heater surface. Accordingly, vapor crowding inhibits the continuous supply of fresh liquid to the heater surface, eventually resulting in premature dryout/critical heat flux (CHF) in comparison to the baseline case of unconfined boiling on the same surface. While studies in literature report the effect of various parameters such as gap dimensions, heater surface to confinement plate area ratio, and surface inclination on confined pool boiling, the role of confinement plate wettability on bubble behavior and heat transfer has yet not been reported. Here we perform controlled experiments to show that superhydrophobic (SHPo) surfaces attract vapor/air bubbles and can be used to enhance heat transfer during confined boiling. In comparison to the typical case of boiling with hydrophilic (HPi) confinement plate, nucleating bubbles underneath a SHPo confinement plate detach easily from the heater surface to provide a continuous pathway for liquid re-supply and heater surface rewetting. Using this strategy, we shown a significant increase of up to 82% in heat dissipation capacity using SHPo confinement plate in comparison to the baseline case of the HPi confinement plate. Detailed parametric investigation of the effect of confinement gap and heater surface to confinement plate area ratio on heat transfer performance is also reported. We believe that the ability to improve confined boiling heat transfer performance by merely tuning the wettability of the confinement plate will find wide applications in two-phase heat sinks for high heat flux applications.