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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Hot-spot cooling by directional transport of jet impinging orthogonally on wettability-patterned surface




Abstract

Spatially-selective cooling is vital in several thermal engineering applications, ranging from electronic devices and gas turbine blades, to nuclear reactors. Although air cooling – primarily due to the associated low cost and favorable dielectric properties – is often used in several applications, it suffers from poor thermal transport properties, which cause poor performance. Better cooling results can be achieved with jet impingement of high Prandtl number liquids. Direct access of the jet to the hotspot is required in order to maximize the cooling in such arrangements – the heat transfer coefficient drops rapidly radially outwards from the jet impingement point. Aligning the jet directly with the hot spot often imposes problems in compact electronic components packaging. To circumvent this issue, we use wettability patterning to lay a diverging superhydrophilic track on a superhydrophobized metallic substrate that mimics the back end of a heat spreader. The liquid jet impinges on the narrow end of the wettable wedge-shaped track, several centimeters from the hot spot. The wettability-confined track carrying the liquid generates a capillary force that diverts the liquid towards the wider track-end, where the hot spot is located. This pumpless, directional transport of the liquid is eventually harnessed for hot-spot cooling. Several track designs are compared for their cooling efficacy. The influence of design and flow parameters, liquid and solid properties, and secondary effects (e.g., thermocapillary transport) related to the unique nature of this cooling approach are evaluated. General guidelines to design an effective and stable system are discussed.

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