Improved modeling of heat transfer in dropwise condensation

摘要

Dropwise condensation has drawn significant attention due to its efficient heat transfer performance compared to filmwise condensation. In this paper, typical experimental data for dropwise condensation on smooth hydrophobic surfaces were collected as well as the typical available heat transfer models. The comparisons between the prediction results and the experimental data indicated that the existing models were not generally applicable to various conditions. A new model for a vertical smooth surface was developed to predict the heat transfer characteristics of dropwise condensation. The new model was based on the nucleation condensation mechanism, and the total heat transfer on the surface includes the heat through all the droplets and the heat through the surface between the droplets. For the latent heat through the droplets the effect of the contact angle was taken into consideration on the basis of the nucleation condensation mechanism. The surface area between the droplets on the surface was thought to be the bare surface, and sensible heat transferred on the bare surface and the droplets surface was viewed as forced convection heat transfer. The calculation results from the model show that, although the heat transferred by forced convection is greatly dependent on the experimental parameters, it is three orders of magnitude smaller than the latent heat through the droplets. Comparisons show that the present model has better prediction precision, with an error range of -35-20% for 87.39% of the data and an error range of -35-25% for 90.37% of the data. The findings obtained from the model suggest that the heat transfer rate and the critical nucleation radius for a single droplet and the droplet size distribution are remarkably affected by the contact angle. In fact, a smaller contact angle enhances the condensation heat transfer and increases the nucleation density. In addition, the thickness of the promoter layer weakens the condensation heat transfer and decreases the nucleation density.