Condensation Enhancement on Hydrophobic Surfaces Using Electrophoretic Method and Hybrid Paint Coating

Abstract

Condensation heat transfer on stainless steel tube utilizing superhydrophobic coatings was investigated. The electrophoretic deposition and spraying methods were employed to coat the tubes’ outer surface. The mixture that was synthesized for spray coating was a hybrid paint. It incorporated polyurethane matrix and a colloidal suspension containing organic nanoparticles. The hybrid paint had a proper adhesion to the substrate which caused more durability compared to the electrophoretic coating. The agglomeration of nanoparticles in the hybrid paint caused the formation of particles with larger size compared to the particles in the electrophoretic coating. Consequently, contact angle hysteresis over electrophoretic coating was much lesser than spraying method. Dropwise condensation regime was observed over both the coatings as a result of hydrophobicity. Nonetheless, the condensation heat flux declined over the hybrid paint at high subcooling temperatures due to transition to the flooding condensation regime. This was due to the accumulation of ultra-small droplets as a result of high nucleation sites. The continuation of droplets sweeping was hindered by sticking to the substrate. The dropwise condensation was maintained over the electrophoretic coating and the transition to the film-wise condensation happened at larger wall subcooling temperature. The ability of the electrophoretic coating in shedding droplets efficiently was caused by higher hydrophobicity, high roughness density, and minimum droplet pinning.

Additional information

Notes on contributors

Sahand Najafpour

Sahand Najafpour received his Bachelor’s degree (2015) and Master’s degree (2018) under the supervision of Prof. Mahmoud Saadat Foumani and Prof. Ali Moosavi; respectively, in mechanical engineering at Sharif University of Technology. He then worked in the nano/micro fluidic lab with Prof. Ali Moosavi in the Center of Excellence in Energy Conversion at Sharif University of Technology as a senior researcher in the Heat Transfer group (2018 till now). His research interests are mainly on functional hydrophobic/hydrophilic coatings, heat transfer enhancement during phase change and interfacial fluid dynamics.

Ali Moosavi

Ali Moosavi received his Bachelor’s degree (1995) and Master’s degree (1997) in mechanical engineering at University of Tehran. He then moved to Lappeenranta University of Technology (Finland) to pursue his studies and worked in the group of Prof. Pertti Sarkomaa on multi-phase transport pheneomena. Then he joined the group of Prof. Siegfried Dietrich at the Max-Planck Institute (Stuttgart) and worked on micro- and nanofluidic systems for more than 4 years. Now he is an associate professor in the mechanical engineering department of Sharif University of Technology.

Hosein Najafkhani

Hosein Najafkhani received his Bachelor’s degree (2014) and Master’s degree (2016) under the supervision of Prof. Abolghasem Dolati in material science and engineering at Sharif University of Technology. He then worked in the nano/micro fluidic lab with Prof. Ali Moosavi in the mechanical engineering department of Sharif University of Technology as a chief researcher in the surface engineering group (2016 till now). Currently he is the CEO of Behsan Nano Taak Co. as a producer of the new generation of the hydrophobic nanocoatings. His research interests focus on fabricating multi-scale hydrophobic coatings for self-cleaning, drag reduction and anti-corrosion properties.