Experimental study on the application of surface wettability difference in condensed water behavior between double surfaces

The difference in surface wettability plays a crucial role in the process of condensation and drainage between fin surfaces. Four surfaces were fabricated: three with homogeneous wettability and one with hybrid wettability. These included a superhydrophobic copper surface (SHO), a hydrophobic copper surface (HOCS), a bare copper surface (BCS), and a hybrid bare/superhydrophilic copper surface (BCS/SHI). Two surfaces were placed vertically with set spacing to simulate fin arrangements, constituting seven different combinations: Combination 1: BCS-HOCS, Combination 2: SHO-BCS, Combination 3: SHO-HOCS, Combination 4: BCS-BCS, Combination 5: HOCS-HOCS, Combination 6: SHO-SHO, and Combination 7: BCS/SHI-BCS/SHI. Due to the presence of wettability difference, the thickness of the liquid film on the BCS/SHI is only about 200 μm, and even at a surface spacing of 1.0 mm, Combination 7 still did not form a liquid bridge. Combination 7 exhibited the highest condensate drainage rate. In Combination 2, the small spherical droplets on the SHO were completely “absorbed” by the adjacent BCS and carried away, preventing liquid bridge formation at a surface spacing of 2.0 mm. Considering both drainage performance and the cost of surface modification, recommended combinations for different spacings are provided. At a surface spacing of 2.0 mm, Combination 2 is the optimal choice. Combination 7 is the best choice when the surface spacings are 1.5 mm and 1.0 mm.