Effects of geometry and dimension of micro/nano-structures on the heat transfer in dropwise condensation: A theoretical study

Condensation is a phase change phenomenon which has many applications in the field of refrigeration, power plants and air-conditioning. It is well-known that dropwise condensation (DWC) has a considerably higher heat transfer than filmwise condensation. DWC occurs on hydrophobic and superhydrophobic surfaces (SHS). Research has shown that micro/nano structures are necessary for producing SHS. The geometry and dimensions of the structures could affect DWC heat transfer. In this research, a numerical study has been done to explore how much the configuration of these structures could change heat transfer in DWC. To attain this goal, two different structures, including semi-conical and semi-pyramidal and their limit states including prismatic and cylindrical structures have been considered. Effects of different parameters including the shape of the structures, roughness factor, and solid fraction on the single droplet and total heat transfer have been studied. Results show that the configuration of structures could significantly affect DWC heat transfer. For instance, at a constant roughness factor and solid fraction, semi-conical or pyramidal pillars have about 2.5-4.5 times higher total heat transfer than prismatic or cylindrical pillars. The shape of pillars could change the small droplet population by about 10%.