Study On Effect Of Solid-Liquid Surface Free Energies Difference On Condensation Heat Transfer Enhancement

In order to study the influence of surface-free-energy difference of solid surface and condensate on the filmwise condensation heat transfer performance, a correlation of the condensation heat transfer coefficient with contact angle has been derived with respect to liquid film flow and heat transfer at vapor-liquid interface. The calculated results for steam filmwise condensation indicate that the heat transfer coefficient increases with the contact angle increasing when the contact angle ranged within a certain degree. When the contact angle is small or approaching 0? the condensation heat transfer coefficient predicted by the correlation is consistent with result of classic Nusselt theory.A series of specially designed experiments are conducted to verify the impact of the surface free energies difference on the dropwise and film condensation heat transfer characteristics. The magnitude of the surface free energies difference is regulated by only changing the condensation surfaces under the identical operation condensation, in particular, the vapor pressure, with the exclusion of thermo properties effect.The steam dropwise condensation heat transfer properties at different condensing pressures are experimentally investigated on a variety of treated surface films, such as ion-implanted Nitrogen surface, mechanically polished surface and diamond-like carbonate (DLCO surface on the substrates of brass and copper plates, respectively. The experimental results indicate that the condensation heat flux and heat transfer coefficient increase with the increasing of the magnitude of the surface free energies difference of the solid surface and the condensate liquid, at the identical operating conditions.Meanwhile, the dependence of filmwise condensation heat transfer on the surface free energies difference of solid surface and liquid on is experimentally studied with the ethylene glycol vapour condensation on surfaces of ion-implanted Nitrogen surface, mechanical polishing surface and DLC surface on the substrates of copper and brass plates, respectively. The experimental obtained heat transfer performance for the treated surfaces is higher than the calculated results of traditional Nusselt theory, also showing the same tendency with those of the correlation established in the present paper.