Self-activated elastocapillary wave promotes boiling heat transfer on soft liquid metal surface

Abstract

Current studies use stiff micro/nano structure to augment boiling heat transfer, there is a superheating boundary layer near the hard structure to dominate the boiling process. Here, comparative studies were performed for pool boiling of ethanol on a hard copper surface and a ~100 μm soft Galinstan liquid metal surface. The latter behaves significant heat transfer enhancement, which is more evident for saturated boiling, under which heat transfer coefficients are raised by 60.5% compared to bare copper surface, maximally. The soft surface decreases bubble departure size by half, and increases bubble departure frequency by ~7 times. These distinct characteristics of bubble dynamics result in the decrease of wall superheating at onset of nucleate boiling from ~13 K on hard copper surface to ~5 K on soft surface. Elastocapillary wave and dynamic wrinkles are observed to disturb the near wall boundary layer for heat transfer enhancement, which are formed by the energy and force interactions between departing bubbles and soft liquid metal. The easier bubble nucleation on soft surface agrees with the bubble nucleation theory for a system including two immiscible liquids. Our study provides an alternative way using self-activated elastocapillary wave to promote boiling heat transfer.