Film boiling heat transfer from micro heat sinks driven by Bénard-Marangoni convection

Abstract

Bénard-Marangoni convection and its significance with regard to film boiling heat transfer from micro heat sinks is discussed. In recent works cooling performance of micro heat sinks has been studied showing that two-phase cooling could be more efficient than single-phase cooling. However, in those previous works was also found that the critical heat flux (CHF) i.e., the transition from a nucleate boiling regime to an almost insulating film boiling regime was the main limitation of two-phase cooling. Here, it is shown that owing to the induced thermal gradient along the fin and the very small fin-spacing, Bénard-Marangoni convection (which was neither considered nor mentioned so far) can play an important role and in fact driven the entire film boiling heat and mass transfer process. The reason behind this lies in the fact that in film boiling the interfacial vapor-liquid velocity is the capital factor rather than the bulk velocity, and this can be at least one order of magnitude higher from Bénard-Marangoni convection. Utilizing a simplified physical model, an analytical expression for the film boiling heat transfer coefficient driven by Bénard-Marangoni was derived. Computational Fluid Dynamics (CFD) simulations were performed and comparison between natural and Bénard-Marangoni convective heat transfer presented