Effect of Mini/Micro/Nanostructures on Filmwise Condensation of Low-Surface- Tension Fluids

摘要

Microanostructured surfaces have been widely explored to enhance condensation heat transfer over the past decades. When there is no flooding, microanostructures can enable dropwise condensation by reducing solid-droplet adhesion. However, microanostructures have mixed effects on filmwise condensation because the structures can simultaneously thin the condensate film and increase the fluid–solid friction. Although oil infusion of structured surfaces has recently been shown to render filmwise condensation dropwise in many cases, challenges remain in the case of extremely low-surface-tension fluids. This work aims to provide a unified experimental platform and study the impact of mini/microanostructures on condensation heat transfer of low-surface-tension fluids in a customized environmental chamber. We first investigate the effect of microstructures, hydrophobic coating, as well as oil infusion on the filmwise condensation of a low-surface-tension fluid, e.g., refrigerant, on microporous aluminum surfaces. And we show that for low-surface-tension condensates, microstructures, hydrophobic coating, or oil infusion do not play a considerable role in enhancing or deteriorating heat transfer. Next, we study how the addition of nanostructures affects the condensation performance of the refrigerant on copper mini-fin structures. It is found that nanostructures slightly deteriorate the condensation performance due to the dominance of solid–liquid friction, although the performance of these mini-fins with nanostructured surfaces is still better than that of the mini-pin-fins. These results provide guidelines of designing mini/microanoscale surface structures for enhanced condensation applications.