On the Critical Role of Surface Tension in Film Condensation onto a Horizontal Cylinder

We explore the subtle role of surface tension on condensate drainage onto a horizontal cylinder. Our study considers a subcooled cylindrical surface exposed to a pool of saturated water vapour. The condensate film flow is assumed to be  steady and laminar. We appropriately reduce the Navier–stokes equations in the cylindrical coordinate system invoking certain assumptions and build a simplified mathematical theory. We model the effects of surface tension by the well-known Laplace formula. We have used the temperature- dependent thermos-physical properties of liquid water for generalisation. The Reynolds’ correlation is used to predict the viscosity of the liquid water. The model governing equations are solved for a suitable set of boundary conditions by the Runge–Kutta method. It is observed that the role of surface tension is predominant near the bottom of the cylinder, whereas it is reasonably weak in the upper part of the cylinder. We found that the film dynamics strongly depend on the cylinder radius. Furthermore, we develop correlations for predicting the local and average Nusselt number, which would be useful for engineering applications.