Abstract
Boiling is an important heat and mass transfer process that has tremendous benefits in thermal management applications where timely and efficient heat removal is critical for operation. Boiling is inherently limited by the critical heat flux (CHF), which is the maximum heat flux that can be dissipated from the heated surface via liquid-to-vapor phase change. Heat fluxes that exceed CHF cause surface dry-out that initiates thermal runaway and eventual device failure or burnout. Past studies have used micro/nanoengineered surfaces to improve wicking and liquid replenishment mechanism to delay CHF and/or increase the CHF limit. In this work, we investigate the CHF limit of micro-nanotextured oil-impregnated surfaces in pool boiling. Pool boiling experiments in water were conducted for copper plates with different surface morphologies, including Krytox oil impregnation. The bubble nucleation, growth, and departure behaviors were captured using a high-speed camera at 1000 frames per second during nucleate boiling. Due to the presence of an annular wetting ridge, which forms near the base of the growing bubble, the bubble growth and coalescence mechanism on oil-impregnated surfaces was distinct from that on un-impregnated micro-nanostructured hydrophobized (i.e., superhydrophobic) surfaces. Our experimental results show that (a) the bubble departure diameter on the oil-impregnated surfaces was 1.6-times larger than that on the superhydrophobic surfaces and (b) the CHF on oil-impregnated surfaces was similar to that on the un-impregnated superhydrophobic surfaces (≈20–30 W/cm2), a result that we attribute to oil depletion. Results show that oil impregnation does not improve the CHF limit in boiling.
