Exploring the limits of condensation heat transfer: A numerical study of microscale-confined condensation between parallel surfaces having wetting contrast

Dropwise condensation has received extensive interest due to its potential to enhance the efficiency of power generation, water harvesting, and thermal management systems. The degree of heat transfer enhancement during dropwise condensation is hindered by the delicate balance between nucleation, droplet growth rate, and condensate shedding. Condensation between parallel surfaces having wetting contrast, termed microscale-confined condensation (MCC), presents a promising method to break the fundamental limits of dropwise condensation by decoupling droplet nucleation and growth from condensate removal. The key mechanisms governing MCC enable spontaneous condensate transfer from the condensing surface to a highly wetting absorbing surface to limit the maximum droplet size. Here, we developed and explored numerical simulations of MCC to elucidate the upper limits of the condensation heat transfer rate. To optimize MCC with respect to heat transfer, we examined the effects of surface gap or maximum droplet size, and condensing surface contact angle on droplet size distribution and overall condensation heat flux. We then developed a regime map in terms of surface wettability and shedding droplet size, and showed that smaller surface gaps and smaller condensing surface contact angles are preferential to achieve a higher heat flux in pure vapor condensation conditions. The optimized MCC outperforms state-of-art condensation including classic dropwise condensation and jumping-droplet condensation, with a 250% enhancement of heat transfer coefficient at a steam temperature of 100 °C. Through numerical simulations, our study not only calculates the upper bound of condensation heat transfer, but also provides guidelines for further enhancement of condensation via decoupling droplet shedding from nucleation.