Optimal contact angle for dropwise condensation: an experimental study

• First experimental validation of optimal contact angle for dropwise condensation, confirming semi-analytical model predictions with experimental data. • Systematic investigation across contact angles from 84° to 115° using self-assembled thiol monolayers on gold-coated smooth surfaces. • Identified an optimal contact angle range (96°–105°) for enhancing condensation heat transfer rate, showing that intermediate, not highly hydrophobic, surfaces yield superior heat transfer rate in dropwise condenation. Dropwise condensation, widely recognized as a highly efficient heat transfer mechanism, is yet to be implemented in industrial applications. Recent advances in semi-analytical modeling of condensation have led to predictions of an optimal contact angle for enhancement of this phase change heat transfer process. Here, we present the first experimental study supporting these predictions. Using self-assembled monolayers of thiols on gold-coated smooth surfaces, we systematically investigated contact angles in the range 84° to 115° in a pressure- and temperature-controlled environmental chamber in the absence of non-condensable gases. Our experimental results reveal that the optimal contact angle for condensation falls between 96° and 105° . Interestingly, while our results support predictions regarding the existence of an optimal contact angle, the specific values and their impact differ from previous reports. By experimentally demonstrating higher condensation heat transfer rates at intermediate contact angles, this study unequivocally shows that high hydrophobicity is not necessarily a desired property for a condenser surface. The insights gained from this work open new avenues for improving dropwise condensation in various industrial processes such as the steam cycle and liquid separation.