A direct numerical simulation study to elucidate the enhancement of heat transfer for nucleate boiling on surfaces with micro-pillars

Abstract

Recent experimental studies have demonstrated great potential of surface engineering in enhancing nucleate boiling heat transfer performance. However, the underlying mechanism remains unclear, especially the role of microlayer evaporation underneath bubbles. In this work, we investigate the heat transfer from microlayer evaporation underneath a growing bubble on micro-pillar arrayed surfaces using Direct Numerical Simulations (DNS). The evolution of the microlayer is reproduced in the DNS by considering a bubble growth driven by the local temperature gradient. The effects of micro-pillar structures on the microlayer profile and the heat transfer performance are systematically studied and analyzed. Our simulation results reveal three distinct microlayer morphologies related to micro-pillar structures: the undisturbed microlayer, the disturbed microlayer, and the disrupted microlayer. It can be further generalized as the greater the spacing and height of the micro-pillars, the more disrupted the microlayer becomes. Due to the reduction of microlayer thickness, more disruption means higher microlayer heat transfer coefficient. However, this accelerates microlayer depletion and thus reduces the overall heat transfer potential from microlayer evaporation during its life cycle in nucleate boiling. Based on these findings, a strategy is revealed for the design of micro-pillar arrayed surfaces to achieve optimal heat transfer performance of the microlayer.