Numerical investigation into transport phenomena of subcooled and saturated flow boiling in large length-to-diameter ratio micro-channel heat sinks

Abstract

This numerical study investigates subcooled and saturated flow boiling of R134a in large length to diameter ratio micro-channel at different mass velocities and heat fluxes. The flow pattern ranging from bubbly flow to annular flow occurs inside large length to diameter ratio micro-channel. This study develops the two-dimensional CFD model for flow pattern which includes bubbly flow, slug flow, and annular flow without any initial conditions for bubble interfaces. The analysis for this CFD model is performed by using the OpenFOAM library. The volume of fluid (VOF) with the phase change model (Lee model) is adopted for capturing the interface between liquid and vapor. To simulate the thermal interaction of solid and fluid regions, the CFD model contains the conjugate heat transfer. Subsequently, the results obtained by numerical simulations and previous experimental research are compared to confirm the validity of the CFD model. The local flow patterns of numerical simulations show good agreement with the flow pattern and bubble behavior of experiments which is captured by high-speed video through the transparent channel top. The predicted void fractions at each location are concurred with the results of the empirical correlation. The computed results which are local channel wall temperatures, heat transfer coefficients, and cross-sectional averaged fluid temperature at the channel outlet agree with the experimentally measured data. The two-dimensional model is hard to simulate the redistribution of liquid films caused by surface tension at the annular flow region along the channel width. Accordingly, there are restrictions to simulate heat transfer phenomena inside the liquid film and dry-out occurring in the annular flow region by using the two-dimensional CFD model. Although the partial dry-out is hard to predict, the characteristic of heat transfer and boiling flow that includes all flow pattern without dry-out is successfully predicted by the current CFD model.