Fluid flow and heat transfer in microchannel devices for cooling applications: Experimental and numerical approaches

Abstract

• Two phase flow in microchannels is characterized by numerical and experimental approaches. • Transition from bubbly flow to slug plug flow is numerically predicted but transition from bubbly flow to churn flow is not. • The proposed numerical tool is sensitive enough to capture particular effects of the studied parameters. Microchannel heat sinks are pointed to have a great potential in cooling systems. This paper presents a systematic study to develop a microchannel heat sink to be used in cooling applications. Particular emphasis is given to PV panels cooling. A systematic experimental approach is used to optimize the heat sink geometry. Then the potential advantage of using flow boiling conditions is explored in both numerical and experimental approaches. The two-phase flow is characterized in two different sets of conditions. In the experimental approach, a constrained bubble flow was observed with a stable pattern and bubble frequency in the narrower channel. In the wider channel a bubbly flow was observed with increased bubble diameters. Numerical simulations were also performed in order to examine the first transient stages of the two-phase flow development close to the inlet of the considered microchannels assuming an initial arbitrary distribution of nucleation sites. For this purpose, a previously developed and validated numerical simulation framework was utilised. The proposed customized tool has been developed in the general context of OpenFOAM CFD Toolbox and it accounts for phase-change (boiling/condensation) as well as for Conjugate Heat Transfer between solid and two-phase flow domains. The numerical predictions reveal that the proposed tool is sensitive enough to capture the effects of channel aspect ratio, applied heat flux and applied mass flux on the generated transient bubble dynamics and the associated heat transfer characteristics and it can constitute an important tool for quantifying the underpinned complex physical mechanisms, providing further insight into the experimental observations and measurements.