Theoretical study of stable dropwise condensation on an inclined micro/nano-structured tube

In this paper, a numerical model for dropwise condensation on a micro/nano-structured inclined tube is developed based on previous theoretical and experimental studies for flat plates. Thermal resistances consisting of conduction through a droplet, vapor-liquid interfacial resistance, droplet curvature, promoter layer, and micro/nano-pillars are included into the model and incorporated in calculating the heat transfer rate across an individual droplet. Droplet morphologies (Wenzel, Cassie, and partially wetting) are considered in the model. Effects of various parameters are investigated on single droplets behaviors and total heat transfer. Results show that average droplets radii on a horizontal tube are higher than on a vertical tube; consequently, vertical tubes have better heat transfer rate. For example, vertical tubes have five times higher overall heat flux than horizontal tubes in some cases. In addition, partially wetting droplets have higher heat transfer rates in comparison with Wenzel or Cassie state in all configurations.