Saturated pool boiling heat transfer from vertically oriented silicon surfaces modified with foam-like hexagonal boron nitride nanomaterials

Abstract

In this work, the ability of a foam-like hierarchical hexagonal boron nitride (h-BN) nanomaterial to act as a scalable surface modifier for improved pool boiling performance is investigated. The h-BN foam samples were grown using an atmospheric pressure chemical vapor deposition process onto the surfaces of open-cell nickel foam followed by selective etching. Saturated pool boiling experiments were conducted in degassed deionized water for unaltered silicon surfaces, silicon surfaces modified with planar or foam-like h-BN materials plus adhesion layer, and a silicon sample with only the adhesion layer present. Results from the unaltered silicon surface obtained in this study were found to be in excellent agreement with previous studies. For the planar h-BN control sample the observed critical heat flux (CHF) occurred at 24.2±2.4W/cm2 at wall superheat of 28.0±2.1K, a factor of three lower CHF than for the unaltered Si surface. CHF for h-BN foam samples occurred at 69.1±6.9W/cm2 at wall superheat of 25.0±2.1K and 87.9±8.8W/cm2 at wall superheat of 24.9±2.1K. These CHF results are comparable to the bare silicon values but significantly enhanced compared to the adhesion layer only and planar h-BN samples, thereby indicating foam-like h-BN nanomaterials have the potential to facilitate significant CHF enhancement but that means of integration is critical to determining overall performance. Comparison of boiling curves reveals the h-BN foam samples demonstrated higher heat transfer coefficient at moderate and high heat flux relative to bare silicon, with CHF being reached at ∼30% lower wall superheat.