Enhancing condensation heat transfer and water harvesting using nanostructured copper surfaces

• SHPB copper reached the highest hD (17,841 W/m 2 .K) via dropwise condensation. • SHPL surfaces collected 1.46 g/h, >65 % more condensate than other surfaces. • SHPL maintained performance after 310 h; SHPB coatings showed degradation. • A 243 mm tube gave the best thermal performance for all surface types. • Clear trade-off: SHPB boosts heat transfer, SHPL ensures durability and water yield. Droplet surface interactions critically influence condensation heat transfer and water harvesting. On hydrophilic surfaces, liquid films increase thermal resistance, whereas on hydrophobic surfaces, dropwise condensation can enhance heat transfer but is sensitive to wetting-state changes. This study evaluates the heat transfer performance, droplet collection efficiency, and long-term durability of bare copper tubes, nanostructured superhydrophilic (SHPL) surfaces fabricated by NaOH-(NH 4 ) 2 S 2 O 8 etching, and superhydrophobic (SHPB) surfaces obtained by PDMS coating. Condensation experiments were performed using a thermoelectric cooler (TEC) and a cooling water-in-tube setup for droplet collection, and a shell-and-tube heat exchanger for heat transfer testing. Consistent results from both setups showed that SHPB surfaces exhibited the highest heat transfer coefficient (hD ≈ 17,841.13 W/m 2 .K) and largest temperature difference (ΔT = 11.7 °C), whereas SHPL surfaces recorded the lowest hD (≈ 2,930.20 W/m 2 .K) and ΔT (10.8 °C). In water harvesting, SHPL surfaces outperformed other samples with an average condensate collection rate of 1.46 g/h, compared to 0.74 g/h for SHPB and 0.87 g/h for bare copper. After 310.24 h of operation, SHPL retained its superhydrophilicity with no measurable contact angle, while SHPB showed partial degradation due to dust and residue accumulation. These findings highlight a trade-off between heat transfer efficiency, droplet collection, and surface stability, and point to the need for hybrid or patterned surfaces to combine the advantages of both wetting states in future applications.