Humid‐Air Condensation Heat Transfer on Hierarchical Structured Superhydrophobic Graphite Composites

ABSTRACT This study investigates wetting behavior, condensation dynamics, and humid‐air condensation heat transfer on stainless steel (SS), an untreated thermally conductive graphite composite (GC), and a hierarchically structured, superhydrophobic graphite composite (SHGC) under varying relative humidity (RH). Static and dynamic contact angle measurements confirm distinct wetting regimes, with SS being hydrophilic (), GC hydrophobic (), and SHGC superhydrophobic (). Condensation experiments reveal that performance is not governed by wettability alone but by a trade‐off between dropwise renewal, droplet pinning, and additional interfacial thermal resistances introduced by hierarchical textures and low‐surface‐energy functionalization. Under saturated conditions (100% RH), GC achieves the highest vapor‐side heat transfer coefficient of , followed by SHGC with , while SS reaches . The lower performance of SHGC compared to GC is consistent with Wenzel‐type pinning and an increased effective thermal resistance during operation. Computational fluid dynamics simulations confirm laminar internal flow in the cooling‐water channel and provide an independent cross‐check of the water‐side heat transfer coefficient used in the resistance‐based evaluation of vapor‐side HTCs. Overall, the results establish graphite composites as promising condenser substrates and highlight that maximizing apparent superhydrophobicity alone does not necessarily maximize condensation heat transfer under humid‐air conditions.