Surface-roughness-boosted critical heat flux enhancement during quenching boiling on wicking surfaces

Abstract

Wicking surfaces have been widely proven to enhance critical heat flux (CHF) by improving liquid replenishment when approaching the dry-out area during vapor bubble evolution within the nucleate boiling regime. However, different than the vapor column growth mechanism for CHF of regular boiling by heating up a surface, during rapid-cooling-induced quenching boiling processes, CHF occurs upon collapse of vapor film within the transition boiling regime, resulting in a difference in the effect of surface properties on CHF. In this work, we show experimentally that the surface wickability is unable to fully elucidate the enhancement of quenching CHF on wicking surfaces with superhydrophilicity, and that the surface roughness could facilitate collapse of vapor film, thus leading to an extra boost of quenching CHF over the contribution of surface wickability. We propose an improved CHF correlation based on the introduction of a roughness-weighted wicking number, which accounts for the extra contribution of surface roughness in breaking the vapor film barrier and promoting the occurrence of wicking phenomena.