LAUSR

Abstract Biphilic surfaces with heterogeneous wettability and hierarchical topography can significantly enhance the condensation heat transfer performance due to the mutual benefits of the hydrophilic patterns and global superhydrophobicity, which facilitate fast nucleation and frequent droplet departure. To investigate the underlying physics of the condensation process on a biphilic surface and further explore the optimal design to achieve preferable heat transfer performance, we develop a comprehensive model that can capture the recurrent transition of filmwise-to-dropwise condensation on biphilic topographies by considering the dynamics of droplet morphology for individual droplet growth and droplet departure, and the associated droplet size distribution. The numerical results indicate that the varying droplet contact angle and the stepwise increase of the droplet contact base area substantially influence the droplet growth and the coalescence-induced droplet departure during the condensation process, and therefore contribute directly to the overall heat transfer enhancement. The model is validated by comparing the results with the heat flux measured in a custom-designed environment chamber. The developed model not only reveals the physics of condensation on biphilic surfaces but also provides important guidelines for the design and optimization of biphilic topographies for high heat flux applications.