Scalable micro/nanostructured superhydrophobic surface modifications for enhanced energy efficiency and heat transfer performance in stainless steel and titanium

Abstract

Condensation refers to the change of a substance from a gaseous phase to a liquid phase, an example of which is the condensation of water vapor in nature. Condensation is used in many industries, such as energy generation and seawater desalination. On a general surface, filmwise condensation is the main phenomenon in which gaseous water vapor is condensed in the form of a film. However, film condensation acts as a factor that reduces energy efficiency as the liquid film formed on the surface interferes with heat transfer. A phenomenon opposite to film condensation is dropwise condensation, which is immediately separated after condensation in the form of droplets, and thus a film is not formed, greatly improving heat transfer efficiency. Because of these advantages, many studies have been conducted, and most studies have induced dropwise condensation by modifying the surface to be superhydrophobic. However, in the case of a superhydrophobic surface, it takes a lot of time and money in the process, so there is a great difficulty in increasing the area. Among them, stainless and titanium, which are most materials for industrial heat exchangers, have high robustness, so there are few studies on improving the condensation performance after surface modification due to the difficulty of processing. For this reason, there is a large gap between the currently conducted studies and the actual industry. Our research team succeeded in modifying the surface of a stainless steel and titanium tube the size of an actual heat exchanger into superhydrophobicity with a simple process. We confirmed that the condensation performance was improved on the superhydrophobic surface through experiments under various conditions. By comparing the improvement in the heat transfer performance of stainless steel and titanium under several conditions, the main cause of the performance improvement was proved. This study is expected to play a major role in the eco-friendly future industry where energy efficiency is important by improving the heat transfer performance of stainless and titanium, which are mainly used throughout the industry.

Superhydrophobicity on AISI 304 stainless steel through surface sensitization process and etching

“…In addition, SH surfaces can be used as a surface for efficient water condensation from vapor phase through the dropwise condensation mechanism, which is different to the condensation mechanism on regular surfaces, i.e., film condensation. Since the film condensation of vapor on the surface (in applications such as heat exchanger) leads to the reduces in the efficiency of the heat transfer [14]. Hence, the super-hydrophobicity on stainless steels which are the common materials used in the industrial heat exchangers is very interesting.…”