Surface roughening for hemi-wicking and its impact on convective boiling heat transfer

Abstract

Superhydrophilicity accompanying hemi-wicking driven by interfacial capillary force can be induced by constructing interfacial structures. We uncover the underlying mechanism for the morphologically driven hemi-wicking, and extend its impact into the practical heat transferring scheme of convective boiling system: the morphologically-driven hemi-wicking on a roughened interface can contribute greatly to the enhancement of boiling heat transfer performance of the convective heat dissipation capacity of critical heat flux (CHF). We present design prerequisites on controlling characteristic lengths of nanoscale interfacial structures that initiate hemi-wicking and consequently enhance boiling performance. Interfacial liquid refreshing through morphologically driven hemi-wicking leads to a greater than 100% increase in CHF by roughening surfaces using vertically aligned silicon nanowire structures (SiNWs). We confirm strong wicking characteristics are essential to increase CHF, however it must be differentiated from surface roughening. Even though the roughening is a prerequisite for leading to the wicking, it can even deteriorate CHF without involving advantage of the interfacial re-wetting. Dimensional prerequisites that initiate hemi-wicking by modulating the characteristic length of SiNWs can be design guidelines for pragmatic engineering applications to enhance feasibility and reliability. We use our findings to put forward a guideline to improve boiling performance, and suggest a way to make breakthrough in heat and energy transfer systems through the functionalized interface.