Is the Surface Wickability the Single Descriptor of Critical Heat Flux During Pool Boiling?

Enhancement and estimation of critical heat flux (CHF) are two of the most important research areas of pool boiling. It is well-known that microstructured surfaces can extend the limit of CHF up to ~250% higher than that of a flat surface. The mechanism for this enhancement has generally been accepted as the wickability of structured surfaces originating from liquid propagation within the surface structures driven by capillary pressure. We investigated the applicability of this theory based on the accumulated data of previous studies and our experimental data. We first calculated capil- lary pressure and permeability of structured surfaces to characterize liquid propagation rate analytically. We then performed pool boiling experiments on silicon micropillar surfaces to measure CHF values.

We found that there is no distinct relationship between the CHF and wickability contrary to a general notion. Results suggest that although liquid wicking has been found to be important, the parameter wickability defined by previous works alone is not sufficient to describe CHF. In addition to the wickability, we propose that there may be other important parameters that also change along with the surface structures, e.g., the diameter of vapor columns and bubble departure size, among others, which need further investigation.