Performance Assessment of Hybrid Microchannel-Pin Fin Heat Sink for Hotspot Thermal Management Under Flow Boiling Conditions

Two-phase microchannel heat sinks are widely used for miniature microelectronic cooling due to their significantly high heat transfer coefficients. However, in complex heterogeneous 2.5D and 3D integrated circuit (IC) architectures, conventional plate-fin microchannel heat sinks often fail to provide uniform cooling across the localized high heat-flux hotspots and low heat-flux background zones owing to their limited heat transfer surface area and eventually result in high temperature gradient, high thermal stress, and ultimate failure. To address this challenge, this paper introduces a novel hybrid microchannel-pin fin heat sink layout consisting of parallel plate-fin microchannels over the background zone and clustered pin fins over the hotspot zone. The clustered pin fins locally increase the surface area in the hotspot region, while parallel plate fins over the background zone ensure uniform coolant flow and avoid flow bypassing around the clustered pin fins. Moreover, parallel plate fins upstream of the hotspot effectively suppress flow boiling instability. A coupled three-dimensional (3D) volume-of-fluid (VOF) and phased-change model has been developed to assess the thermal-hydraulic performance of the proposed hybrid microchannel-pin fin heat sink under flow boiling conditions over a wide range of hotspot heat flux using saturated water as coolant. The flow boiling performance of the hybrid microchannel-pin fin heat sink has also been compared with the conventional plate-fin microchannel heat sink. The results obtained from the developed numerical model reveal that the proposed hybrid microchannel-pin fin heat sink layout effectively dissipates both background and hotspot heat fluxes and subsequently, enhances temperature uniformity across the hotspot and background zones with a marginal increment in pressure drop compared to the conventional microchannel heat sink. The numerical model provides deep insights into the bubble dynamics and corresponding transient thermal-hydraulic response, which can be used for the optimization of the hybrid microchannel-pin fin heat sink layout.