Limits of dropwise condensation heat transfer on dry nonwetting surfaces

Surface condensation is ubiquitous in applications such as power generation and desalination. Nonwetting surfaces have been studied extensively for their dropwise condensation potential with reports of dramatic improvements relative to the classical Nusselt equation for film-wise condensation that has long served as a reference theoretical <i>lower bound</i> on the condensation heat transfer coefficient. However, a theoretical <i>upper bound</i> on the <i>maximum</i> possible condensation heat transfer over a given surface is not available. Considering actual surface topographies as fractal surfaces, we present theoretical upper bounds for gravity-driven and jumping droplet condensation modes in a unified manner. Experimental data on steam condensation from this study as well as the literature on dry nonwetting surfaces are compared to the bounds to identify the opportunity gap to the theoretical maximum. Solid-infused surfaces, introduced recently by the authors, are shown to fall in this opportunity space, closer to the upper bound.