Analysis of Confined Jet Impingement in Converging Annular Microchannel Heat Sinks

Abstract

Jet impingement cooling is deemed an excellent choice for the thermal management of high-power electronics. However, high-pressure drop penalties and low local heat transfer coefficients in regions far from the jet zone are its drawbacks. Although it is reported that recirculation areas appear because of the entrainment, the effects of recirculation size on thermal behavior are not understood well enough. Here, jet impingement heat sinks with converging annular channels are employed in a numerical investigation to minimize the adverse cooling effects associated with an impinging jet in a microchannel. The realizable $k-\epsilon$ turbulent model is used for modeling thermal and turbulent flow fields ($\mathrm{Re}=\mathrm{5,000}$ to 25,000). It was found that the different flow recirculation zones in small scales are responsible for the enhanced heat transfer rate. While the thermal performance of a converging wall jet impingement heat sink is higher than its flat wall counterpart at low $\mathrm{Re}$ numbers, the thermal performance results are in favor of the flat wall jet impingement heat sink at high $\mathrm{Re}$ numbers. The flow recirculation area shrinks in converging channels at high $\mathrm{Re}$ numbers, thereby deteriorating the thermal performance of the converging channel compared with a flat wall jet heat sink. Also, it was found that employing steeper converging channels shrinks the flow recirculation region, resulting in up to 59% lower pressure drops at $\mathrm{Re}=\mathrm{25,000}$. The present study examines the role of flow recirculation at different $\mathrm{Re}$ numbers on the thermohydraulic performance of jet impingement converging annular heat sinks.