Optimized Expanding Microchannel Geometry for Flow Boiling

Abstract

This study discusses the simulation of flow boiling in a microchannel and numerically predicts the effects of channel geometry variation along the flow direction. Experimental studies by Pan and collaborators and suggestions from Mukherjee and Kandlikar have generated interest in expanding the cross section of a microchannel to improve boiling heat transfer. The motivation for this geometry change is discussed, constraints and model selection are reviewed, and Revellín and Thome's critical heal flux criterion is used to bound the simulation, via MATLAB, of separated flow in a heated channel. The multiphase convective heat-transfer coefficient is extracted from these results using Qu and Mudawar' s relationship and is compared to reported experimental values. Expanding channel geometry permits higher heat rates before reaching critical heat flux.

Flow patterns and heat transfer mechanisms during flow boiling over open microchannels in tapered manifold (OMM)

“…Previous research efforts in this area have focused on overcoming these challenges by using various structures, such as inlet restrictors [8], artificial nucleation sites [9], reentrant cavities [10], vapor venting [11] and increasing flow cross-sectional area [12,13]. Further details on these techniques that provide enhanced heat transfer and reduced flow instability have been addressed in a previous publication by the authors [14].…”

A thermosiphon loop for high heat flux removal using flow boiling of ethanol in OMM with taper

“…They found diverging microchannels instrumental in stabilizing the flow, with artificial nucleation sites enhancing heat transfer performance and minimizing wall temperature. Miner et al [14] numerically studied the effect of microchannel with expanding base on flow boiling performance. Their model used CHF as a measure of performance enhancement in microchannels.…”