Experimental investigation on steam condensation heat transfer enhancement with vertically patterned hydrophobic-hydrophilic hybrid surfaces

The maximum droplet radius and droplet size distribution are significant for dropwise condensation heat transfer. Adjusting the maximum droplet radius and droplet size distribution with vertically patterned hydrophobic-hydrophilic hybrid surface is an effective method to enhance and optimize condensation heat transfer performance. The maximum droplet radius and droplet size distribution adjustment with hydrophobic-hydrophilic hybrid surface, and the resultant heat transfer performance are investigated experimentally in this paper. The results indicate that with the increase of hydrophobic region width, the maximum droplet radius on hydrophobic region increases while the droplet population density decreases. An optimum hydrophobic region width exists and the steam condensation heat transfer performance decreases with the increase of hydrophilic region width. And the performance can be larger than that of complete dropwise condensation for appropriate hybrid surfaces. The steam condensation heat transfer performance on the optimum hybrid surface is about 23% higher than that of complete dropwise condensation at surface subcooling of 2.0 K. Steam condensation heat transfer enhancement factor increases with the increase of hydrophobic region width first and then decreases with its further increase. The optimum hydrophobic region width is about 0.55 mm and the corresponding optimum maximum droplet radius is about 0.25 mm. Heat transfer enhancement factor decreases with the increase of surface subcooling and the optimum heat transfer enhancement factor is also significantly dependent on the surface subcooling. When the surface subcoolings are 2.0 K, 4.0 K and 6.0 K, the optimum heat transfer enhancement factors are about 1.23, 1.11 and 1.07, respectively. Steam condensation heat transfer can be enhanced with hydrophobic-hydrophilic hybrid surface more effectively at low surface subcooling. The experimental results and theoretical analysis agrees well to each other.