Understanding the non-isothermal fluid dynamics of the annular flow boiling regime inside a microchannel*

Flow boiling inside microchannel heat sinks have been recognized as one of the efficient ways of cooling advanced electronic devices which generate high heat such as micro-electronic chips, micro-electro-mechanical systems (MEMS), fuel cells etc. Extensive research has been carried out in the past to understand the heat transfer characteristics inside a single microchannel using numerical simulations, however, the focus has been mainly on elongated slug/confined bubble regime. While such flow pattern does dominate near the upstream of the microchannel, film evaporation in annular flow becomes prominent at the downstream, but the flow dynamics in annular flow are relatively poorly understood. In the present work, three dimensional numerical simulations have been performed to understand the fluid flow dynamics and heat transfer associated with the annular flow regime inside microchannels. For this purpose, direct numerical simulations are carried out using the volume-of-fluid method with an additional model to handle liquid-vapour phase change. Furthermore, bubble nucleation is found to occur even in the thin annular film, hence an attempt will also be made to understand the dynamics of such bubbles nucleating in the thin annular film and its effect on flow boiling instabilities.