Nano/micro-scale surface modifications using copper oxidation for enhancement of surface wetting and falling-film heat transfer

The copper oxidation in NaOH aqueous solutions by a chemical immersion method was used to create nano/micro-scale surface morphology on heat transfer surfaces and control their liquid wettability. Different oxidation conditions, depending on nano/micro-scale surface morphologies, created hydrophilic surfaces (contact angle < 90°) with nano-whisker structures of CuO, and hydrophobic surfaces (contact angle > 90°) with nano/micro-crystal structures of Cu2O. A heat transfer experiment using a horizontal-tube, falling-film evaporator was performed to study the effect of the nano/micro-scale surface morphology of the evaporator tubes on surface wetting and heat transfer. The surface wetting and heat transfer performance of three different evaporators of plain (untreated), oxidized, and porous-layer coated tubes were compared.