Ultrathin Durable Organic Hydrophobic Coatings Enhancing Dropwise Condensation Heat Transfer

Abstract

Organic hydrophobic layers targeting sustained dropwise condensation are highly desirable but suffer from poor chemical and mechanical stability, combined with low thermal conductivity. The requirement of such layers to remain ultrathin to minimize their inherent thermal resistance competes against durability considerations. Here, we investigate the long-term durability and enhanced heat-transfer performance of perfluorodecanethiol (PFDT) coatings compared to alternative organic coatings, namely, perfluorodecyltriethoxysilane (PFDTS) and perfluorodecyl acrylate (PFDA), the latter fabricated with initiated chemical vapor deposition (iCVD), in condensation heat transfer and under the challenging operating conditions of intense flow (up to 9 m s –1 ) of superheated steam (111 °C) at high pressures (1.42 bar). We find that the thiol coating clearly outperforms the silane coating in terms of both heat transfer and durability. In addition, despite being only a monolayer, it clearly also outperforms the iCVD-fabricated PFDA coating in terms of durability. Remarkably, the thiol layer exhibited dropwise condensation for at least 63 h (>2× times more than the PFDA coating, which survived for 30 h), without any visible deterioration, showcasing its hydrolytic stability. The cost of thiol functionalization per area was also the lowest as compared to all of the other surface hydrophobic treatments used in this study, thus making it the most efficient option for practical applications on copper substrates.

Out-of-Plane Biphilic Surface Structuring for Enhanced Capillary-Driven Dropwise Condensation

“…On the other hand, hydrophobic surfaces usually enable dropwise condensation wherein water droplets nucleate, grow, coalesce, and depart periodically. This leads to a significantly higher overall heat-transfer coefficient. − For this reason, several works in recent years have investigated surface characteristics enabling passive, controlled droplet departure during dropwise condensation on metallic surfaces. − …”

“… 3 − 5 For this reason, several works in recent years have investigated surface characteristics enabling passive, controlled droplet departure during dropwise condensation on metallic surfaces. 6 − 10 …”

Hybrid nanofluid flow over a slippery surface for thermal exploration

“…Viewed in this way, the attention of many researchers and scientists has gathered in a concerted effort to analyze heat and mass transfer. [1][2][3] Scientists and scholars introduced a novel class of liquid they declared ''nanofluids'' (NF) as a result of solids' superior heat transmission characteristics to those of ordinary fluids. 4 Gowda et al 5 scrutinized the impact of activation heat with chemical reactions on energy transmission of the Marangoni flow of a non-Newtonian nanofluid.…”

Acrylonitrile Butadiene Polystyrene–SiO2 Composite Nanostructures for Self-Regulated Superhydrophobic Liquid Dosage Systems

“…The binder increases the durability of the coating against mechanical abrasion; however, it sometimes adversely affects the performance of the coating. In particular, when a superhydrophobic polymer coating is applied for enhanced condensation heat transfer through heat exchanger tubes, phenomena such as “blistering” can occur at the coating-tube interface, which decreases the overall heat-transfer performance of the system. , Therefore, a coating should be firmly attached to the substrate surface without any imperfections. In our previous report, we introduced a binder-free coating strategy for developing a durable superhydrophobic nanostructured coating over the polymer surface through a simple dip-coating process, where the superhydrophobicity was established by the swelling and self-stratification processes of the polymers in good solvents .…”