Study on the flow and evaporation characteristics of falling film on dot-matrix hydrophilic-hydrophobic composite surfaces

A new method for enhancing falling film evaporation through wettability modification was introduced in this study, which is different from enhanced pool boiling and flow boiling. The dot-matrix hydrophilic-hydrophobic composite surface is proposed as a novel strategy to actively regulate liquid film dynamics and cause liquid film disturbances to improve evaporation heat transfer. In order to study the enhancement of falling film evaporation heat transfer by hydrophilic-hydrophobic composite surfaces, an experimental system and a comprehensive mathematical model were established. The effects of wettability, surface structure and superheat degree on film flow and heat transfer were also investigated theoretically and experimentally. The mathematical model is coupled with the surface tension model based on the volume of fluid model, enabling quantitative prediction of liquid film evolution and evaporation. The results indicate that regardless of the combination of the wettability on the composite surface, its heat transfer coefficient is always greater than that of the surfaces with uniform wettability. Heat flux of the composite surface under the optimal combination can be increased by 139.7% compared with the uniform surfaces. It reveals the hydrophobic regions effectively cause the liquid film to undergo periodic flow and convergence around it, which accelerates the flow field and enhances the heat transfer efficiency. This research not only provides a new idea for enhancing the falling film evaporation through wettability modification, but also offers references for the design of enhanced surface evaporation.