Publication

Even though dropwise condensation (DWC) has received significant attention for its potential to enhance heat transfer performance at a higher order than filmwise condensation (FWC), the scalability of durable DWCpromoting surfaces to sustain prolonged condensation remains challenging. The spray coating presents itself as a potential scalable method to deposit hydrophobic coating onto a metallic substrate. However, the conventional sprayable fluoropolymer exhibits poor adhesion to the substrate and thus requires a base coat before it can be deposited on a metallic substrate. To address this challenge, this study investigated dropwise condensation performance on a polytetrafluoroethylene/imide-based binder/copper oxide composite (PTFE/PI/CuO) coating that is deposited into a copper substrate using simple one-step spray coating and thermal annealing. The PTFE particles provide the necessary hydrophobic characteristics. At the same time, the polymer binder fills the pores between the particles, preventing droplet nucleation within the structure and minimizing the occurrence of flooding that can lead to undesirable droplet pinning. The PTFE/PI/CuO coating successfully promotes pinnedfree dropwise condensation, leading to approximately two times higher heat transfer enhancement than filmwise condensation. Moreover, the formation of micro-scale hydrophilic CuO clusters at the top of the coating surface acts as nucleation sites that increase droplet growth rate and departure frequency without altering the droplet departure radius. As a result, PTFE/PI/CuO exhibits 1.4x times higher heat transfer over the PTFE/PI. Furthermore, a durability enhancement was obtained by adding sub-micron copper particles. While PTFE/PI coating failed after exposure to steam, no visible damage was observed from PTFE/PI/CuO, thus indicating enhanced durability. Moreover, the PTFE/PI/CuO composite also exhibited resistance against mechanical damage as its heat transfer performance remained similar even after being subjected to abrasion. Finally, the pull-off adhesion test revealed that PTFE/PI/CuO has higher adhesion strength than PTFE/PI, making it more suitable for dropwise condensation application.