Substrate thermal conductivity-mediated droplet dynamics for condensation heat transfer enhancement on honeycomb-like superhydrophobic surfaces

The efficiency of dropwise condensation heat transfer has been improved significantly by the development of superhydrophobic surfaces, which are usually fabricated by coating a thin superhydrophobic layer on different kinds of substrates (e.g., different metals/alloys). However, the effects of the thermal conductivity of the substrate on condensation heat transfer over such superhydrophobic surfaces remain unclear. In this paper, we investigated experimentally the condensation heat transfer and droplet dynamics on honeycomb-like superhydrophobic (HCLS) surfaces with hierarchical microporous structures, fabricated by an electrochemical method on four metallic substrates with different thermal conductivities, i.e., copper, brass H96, brass H65 and stainless steel SS316. We observed spontaneous droplet jumping on all these HCLS surfaces at a relatively low degree of subcooling. We also demonstrated the interplay between the substrate thermal conductivity and condensation heat transfer performance during the flooding condensation transition (FCT) by numerical simulations. In the jumping-droplet condensation and flooding condensation regimes, the condensation heat flux and heat transfer coefficient were found to be almost unchanged for different substrates. However, the substrate with a higher thermal conductivity leads to a higher condensation heat transfer coefficient as well as a higher droplet departure frequency at moderate degrees of subcooling, indicating the synergistic effect between the substrate thermal conductivity and droplet dynamics during FCT. The substrate thermal conductivity-mediated droplet dynamics enables a way for further enhancing condensation heat transfer on the HCLS surfaces. © 2021 Elsevier Ltd