Role of Wickability on the Critical Heat Flux of Structured Superhydrophilic Surfaces

TLDR

Superhydrophilic coatings improve pool boiling critical heat flux, but the influence of nanostructures on this enhancement remains unclear. Biotemplating with Tobacco mosaic virus produced surfaces of diverse scales, morphologies, and roughness, and wickability was quantified by a wicked volume flux parameter analogous to contact angle to assess its impact on CHF. Wickability alone governs CHF on structured superhydrophilic surfaces, as shown by repeatable results across varied substrates, morphologies, and scales, yielding a validated correlation and a record CHF of 257 W cm⁻² for water.

Abstract

While superhydrophilic coatings with enhanced wetting properties have been shown to increase the pool boiling critical heat flux (CHF), the role of nanostructures on its enhancement is not clear. Here, biological templates have been used to demonstrate that wickability is the single factor dictating CHF on structured superhydrophilic surfaces. The flexibility of biotemplating using the Tobacco mosaic virus has been leveraged to create surfaces with varying scales, morphologies, and roughness factors. Their wickabilities have been quantified via the wicked volume flux, a phenomenological parameter analogous to the contact angle, and the role of wickability on CHF has been demonstrated using data from over three dozen individual surfaces. These results are repeatable and independent of the substrate material, surface fouling, structure material, morphology, and contact angle as well as the structure scale. An experimentally validated correlation for CHF has been reported on the basis of the dimensionless wickability. Additionally, the surfaces have achieved a CHF of 257 W/cm(2) for water, representing the highest reported value to date for superhydrophilic surfaces. While the role of wickability on CHF has often been cited anecdotally, this work provides a quantitative measure of the phenomena and provides a framework for designing and optimizing coatings for further enhancement.