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Thermal management is one of the most challenging problems of electronic devices today. As technology becomes increasingly miniaturized, extremely localized heat dissipation leads to the challenge of keeping devices away from overheating. Flow-boiling microchannel heat-sinks exploit the highly efficient thermal energy transport of phase change from liquid to vapor. However, the excessive consumption of liquid-phase by highly localized heat source causes the two-phase flow maldistribution, leading to greatly reduced heat transfer coefficient, high-pressure loss, and limited flow rate. In this study, we investigate two-dimensional flow-boiling morphological characteristics in a microgap with hydrophilic coating on hot-spot. The experiments are carried out on a Stainless Steel plate having a micro gap depth of 254 μm using deionized water with inlet at room temperature. A partial hydrophilic surface is created on the hot-spot (surface above the heater) which forms a wettability difference along the metal plate. A wide range of mass flux and heat flux are considered to quantify heat transfer coefficient. In addition, high-speed flow visualizations are performed to characterize the nucleation and bubble dynamics in flow boiling.

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As technology becomes increasingly miniaturized, thermal management becomes challenging to keep devices away from overheating due to extremely localized heat dissipation. Two-phase cooling or flow-boiling in micro-spaces utilizes the highly efficient thermal energy transport of phase change from liquid to vapor. However, the excessive consumption of liquid-phase by highly localized heat source causes the two-phase flow maldistribution, leading to a significantly reduced heat transfer coefficient, high-pressure loss, and limited flow rate. In this study, flow-boiling in a two-dimensional microgap heat sink with a hydrophilic coating is investigated with bubble morphology, heat transfer, and pressure drop for conventional (non-hydrophilic) and hydrophilic heat sinks. The experiments are carried out on a stainless steel plate, having a micro gap depth of 170 µm using deionized water at room temperature. Two different hydrophilic surfaces (partial and full channel shape) are fabricated on the heated surface to compare the thermal performance with the conventional surface. Vapor films and slugs are flushed quickly on the hydrophilic surfaces, resulting in heat transfer enhancement on the hydrophilic heat sink compared to the conventional heat sink. The channel hydrophilic heat sink shows better cooling performance and pressure stability as it provides a smooth route for the incoming water to cool the hot spot. Moreover, the artificial neural network prediction of heat transfer coefficient shows a good agreement with the experimental results as data fits within ±5% average error.

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