Analysis of condensation heat transfer on hydrophilic-hydrophobic composite surfaces considering droplets dynamic behavior

Abstract

In order to reveal the enhancement effect of the hydrophilic-hydrophobic composite structure surface on condensation heat transfer and the effects of dynamic behavior characteristics of condensate droplets, an experimental system and a mathematical model of condensation on the hydrophilic-hydrophobic composite surface was established. The model is based on the theories of dropwise condensation (DWC) and filmwise condensation (FWC), in combination with the effects of droplets nucleation, coalescence, detachment, and sliding sweeping. The effects of surface structure size, wettability, operating temperature and droplet dynamic behavior on condensation efficiency were analyzed by the model. The surface has circular hydrophobic patterns with a diameter of W_DWC and hydrophilic channels separated by W_FWC. The results show that under the same conditions, the condensation heat transfer coefficient increases first and then decreases with the increase of W_DWC, and there is only one optimal W_DWC corresponding to W_FWC, which maximizes the condensation heat transfer coefficient. Moreover, the optimal W_DWC is only affected by W_FWC and is insensitive to other factors. The average condensation heat transfer coefficient of the optimal structure size can be increased by 78.8 % and 316.6 % compared with that of the completely hydrophobic surface and hydrophilic surface. The results illustrate the possibility of enhanced condensation with composite surfaces, which provide guidance for the design and preparation of composite surfaces with hydrophobic patterns for enhanced heat transfer in steam condensation.