Investigation of the effect of maximum droplet radius on condensation heat transfer on hydrophobic-hydrophilic hybrid surfaces with the effect of Marangoni convection

Condensation occurs in two modes, including filmwise and dropwise condensation. On a hybrid surface, the maximum radius of the condensed droplet on the surface in the dropwise region significantly affects the rate of heat transfer. In this paper, the effect of maximum droplet radius on heat transfer on hybrid surfaces is investigated. In this paper, the effect of Marangoni convection-current due to the temperature gradient- is considered as a resistance in the heat transfer process. The results indicate that an optimum value of the maximum droplet radius exists to enhance the condensation heat transfer of steam in the hybrid surface that is dependent on the surface subcooling degree, filmwise region width and the contact angle. As the surface subcooling degree increases from 1.0 K to 10 K, the optimum maximum radius of the droplet in the dropwise region increases from about 0.25 mm to 0.3 mm. Also, the optimum maximum radius of the droplet increases from about 0.25 mm to 0.35 mm when the filmwise region width is increased from 0.5 mm to 1.0 mm. Finally, the results of applying the effect of Marangoni convection indicate a 30% increase in the heat transfer coefficient in the case of applying Marangoni convection.