Improved Heat Transfer Modeling of Moist Air Condensation on Hydrophobic Metallic Surface

For dropwise condensation of water over a textured surface, the condensation rate is limited by the conduction resistance of the droplet. Conduction models with varying levels of approximation have been reported in the literature. In the present study, the conduction resistance of a spherical-cap droplet is derived by regression analysis of data generated by 3D numerical simulation. Results show that conduction resistance is sensitive to the choice of contact angle and droplet radius. The proposed model has significant differences from reported models which are based on 1-D and 2-D approximations. An important source of discrepancy is traced to additional heat flux localized at the three-phase contact line. Equivalently, high local heat flux serves to lower thermal resistance between the vapor-liquid interface and the condensing wall. The prediction of the droplet growth rate using the proposed conduction model is in good agreement with the experiments reported in the literature. The improved conduction resistance correlation is incorporated in the model for a space- and time-resolved dropwise condensation cycle for vapor condensing from moist air. Simulations with the improved condensation model show close agreement with experimental data, justifying the utility of an improved correlation for conduction resistance.