A computational study on the effects of surface tension and Prandtl number on laminar-wavy falling film condensation

[+] Author and Article Information
Mahdi Nabil

Department of Mechanical and Nuclear Engineering The Pennsylvania State University University Park, PA, 16802

Alexander S Rattner

Department of Mechanical and Nuclear Engineering The Pennsylvania State University University Park, PA, 16802

1Corresponding author.

ASME doi:10.1115/1.4037062 History: Received June 04, 2016; Revised June 04, 2017


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 many 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, and Capillary 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 evaluate interface dynamics accurately. The numerical model is first validated for smooth falling-film condensation heat transfer and wavy falling film thickness. The simulation approach is applied to isolate and quantify Nusselt number variations with Reynolds, Prandtl, and Capillary numbers. Finally, based on the collected simulation data, a new Nusselt number correlation for laminar-wavy falling film condensation is proposed.

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