Characteristics of microlayer formation and heat transfer in mini/microchannel boiling systems: A review

Abstract

This paper reviews recent research on microlayer formed by confined vapor bubbles during boiling in mini/microchannels. Experimental measurements, simulations and theoretical studies are described and compared. As a reference to clarify the mechanism for the formation of a microlayer, Taylor flow (i.e. elongated bubble flow in mini/micro circular tubes under adiabatic conditions and at Re << 1) and elongated bubble flow at high velocity, with consideration of the influence of inertia, are also reviewed. Compared to the steady adiabatic conditions, one of the distinct points for the boiling condition is that the bubble grows exponentially due to rapid evaporation of the microlayer. A pattern of two regions (i.e., surface tension-viscosity controlled and boundary layer controlled regions) seems to be presently acceptable to describe microlayer formation for a wide range of bubble growth velocity. In addition, the effect of microlayer evaporation on the boiling heat transfer in mini/microchannel is reviewed.