Condensation heat transfer of CO₂ on Cu based hierarchical and nanostructured surfaces

Phase-change processes such as condensation are efficient means of heat transfer. However, condensation is also an energy-intensive process and extensive research is conducted to increase the heat transfer efficiency. Increasing the effective heat transfer area in terms of surface structures on macro or microscale is one such technique of heat transfer enhancement. In this work, we have studied micro- and nanostructured surfaces for their potentials in increasing heat transfer during condensation of CO₂. Three Cu-based surfaces on which CuO nanoneedles have been grown, have been investigated. We hypothesize three competing mechanisms govern the overall heat transfer on structured surfaces: 1) increased heat transfer area, 2) lower thermal conductivity of oxides, and 3) condensate flooding of the structures. Our study has shown that in some cases, the effect of these mechanisms can be neutralized. More importantly, the results show that superior heat transfer can be achieved by optimizing the surface structure. The best of the structured surfaces resulted in a heat transfer coefficient 66% higher than that of the unstructured surface.