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Test surfaces promoting liquid spreading at a contact angle less than 10°. (a) SEM images and (b) apparent static contact angle. As the anodic oxidation time increases, surfaces develop nano, micro/nano, and microstructures in that order. Surfaces composed of nanostructures (or nanotubes) have near-complete wetting (2°–9.2°). Micro/nano and microsurfaces have perfect complete wetting (0°). Their CHF values could not explained by only wettability effect as Fig. 2.
CHF experimental data and Kandlikar’s prediction [CHF enhancement ratio: . At a contact angle less than 10°, the liquid spreading on a heating surface is the dominant CHF enhancement mechanism. (a) nanostructure, (b) nanostructure, (c) micro/nanostructure, and (d) microstructure.
Liquid spreading model for the absorption layer. The difference between the volumes of the original and the remained (spreading) droplets is the volume of the liquid absorbed by the absorption layer. (a) Calculation concept of the absorbed liquid volume through the dynamic wetting test of liquid droplet. (b) The curvature radius and the dynamic contact angle on microstructured surface. The available region consisted both advancing and spreading by precursor layer inside micro, nano, and micro/nanostructures (Ref. 15). (c) Schematic diagram of the CHF model including liquid spreading.
CHF values of experimental data and the developed prediction based on Eq. (2). The heat fluxes due to liquid spreading are: (a) nanostructure: , (b) nanostructure: , (c) micro/nanostructure: , and (d) microstructure: . The micro/nanoduplicated structure has the highest CHF value due to its having the most liquid spreading.
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