Spatially-selective cooling by liquid jet impinging orthogonally on a wettability-patterned surface

• Directional jet impingement cooling using wettability patterning.
• Water jet impinging orthogonally on surface is redirected laterally.
• Single and two-phase heat transfers are investigated in open-air heat exchanger.
• Two-phase heat transfer showed ∼4 times higher efficiency than closest competitor.
• Cooling of multiple spots is demonstrated using multiple patterned tracks.

Jet impingement finds application in high-rate cooling because of its numerous merits, which, however, do not include selective directionality. The present study introduces a new configuration employing a wettability-patterning approach to divert an orthogonally-impinging laminar water jet onto a pre-determined portion of the target surface. Diverging wettable tracks on a superhydrophobic background provide the means to re-direct the impinging jet and enable spatially-selective cooling on the heated surface. An open-surface heat exchanger is constructed using this approach, and its heat transfer performance is characterized. Sensible heat transfer is quantified in terms of the extracted cooling flux and the heat transfer coefficient. Since this approach facilitates prolonged liquid contact with the underlying heated surface through thin-film spreading, evaporative cooling is also promoted. Thus, phase-change heat transfer is also facilitated, and results in the extraction of 12.4 W/cm2 at water flow rate of ∼1.5 mL/min. By comparing with other jet-impingement cooling approaches, the present method provides roughly four times more efficient cooling by using less amount of coolant. The reduced coolant use, combined with the gravity-independent character of this technique, offer a new paradigm for compact heat transfer devices designed to operate in reduced- or zero-gravity environments. Multiple hot spot cooling is also demonstrated using a single jet to feed two different tracks by minimally displacing or splitting the impinging jet.

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