A Computational Study on the Effects of Surface Tension and Prandtl Number on Laminar-Wavy Falling-Film Condensation

Characterization of wavy film heat and mass transfer is essential for numerous energy-intensive chemical and industrial applications. While surface tension is the underlying cause of film waviness, widely used correlations for falling-film heat transfer do not account for surface tension magnitude as a governing parameter. Furthermore, although the effect of Prandtl number on wavy falling-film heat transfer has been highlighted in some studies, it is not included in most published Nusselt number correlations. Contradictory trends for Nusselt number variation with Prandtl number are found in correlations that do account for such effects. A systematic simulation-based parametric study is performed here to determine the individual effects of Reynolds, Prandtl, capillary, and Jakob numbers on heat transfer in laminar-wavy falling-films. First-principles based volume-of-fluid (VOF) simulations are performed for wavy falling condensation with varying fluid properties and flow rates. A sharp surface tension volumetric force model is employed to predict wavy interface behavior. The numerical model is first validated for smooth falling-film condensation heat transfer and wavy falling-film thickness. The simulation approach is applied to identify Nusselt number trends with Reynolds, Prandtl, capillary, and Jakob numbers. Finally, based on the collected simulation data, a new Nusselt number correlation for laminar-wavy falling-film condensation is proposed.