CONDENSATION PHASE CHANGE BEHAVIORS ON A ROUGH SURFACE CHARACTERIZED BY FRACTAL CANTOR

Abstract

Understanding the fundamental mechanisms of vapor condensation on rough surfaces is crucial to a wide range of industrial applications. A hybrid thermal lattice Boltzmann model of the condensation heat transfer process on downward-facing rough surfaces characterized by the Cantor fractal is developed and numerically analyzed to investigate the condensation phase change behaviors on rough hydrophobic and hydrophilic surfaces. The dynamic behaviors of vapor condensation, including the evolutions of vapor–liquid interface, heat flux, condensate mass, and temperature distribution, on the hydrophilic and hydrophobic rough surfaces are presented and compared with corresponding smooth surfaces. The results indicate that the rough surface preferred a filmwise condensation under hydrophilic conditions but a hybrid dropwise–filmwise condensation under hydrophobic conditions. On the rough hydrophobic surface, the liquid film can rapidly adsorb droplets, maintaining a high-efficiency dropwise condensation. The absorption of droplets accelerates the liquid film growth and detachment process on the rough hydrophobic surface, which reduces the time-averaged thermal resistance of the filmwise region. These two behaviors together enhance condensation heat transfer on the downward-facing rough hydrophobic surface. Besides, stable dropwise condensation could also be formed on smooth hydrophilic surfaces and has better heat transfer performance than corresponding hydrophobic surfaces under the same heat transfer condition.