VOF MODELING AND ANALYSIS OF FILMWISE CONDENSATION BETWEEN VERTICAL PARALLEL PLATES

Abstract

In this study, a computational model has been developed to predict condensation heat transfer between vertical parallel plates. Transient simulations of filmwise condensation in a small two-dimensional parallel plate passage are performed. The Volume of Fluid (VOF) method is used to track the vapor liquid interface. The Geometric Reconstruction Scheme, which is a Piecewise Linear Interface Calculation (PLIC) method, is employed to keep the interface sharp. The governing equations and the VOF equation with relevant source terms for condensation are solved explicitly. The surface tension is taken into account in the modeling and it is evaluated by the Continuum Surface Force (CSF) approach. Different methods to evaluate the source terms in the VOF and energy equations are summarized based on previous studies. The simulation is performed using the CFD software package, Ansys Fluent, and an in-house developed code. This in-house code is specifically developed to calculate the source terms associated with phase change, which are deduced from the Hertz-Knudsen equation based on the kinetic gas theory. The predicted results show that a laminar regime exists at the top of the wall, where the film is the thinnest. A wavy regime appears as a series of regular ripples/waves of condensate moving downwards under the action of both gravity and shear stress in the interface area. As a further step, the simulations have been run under different surface tension, wall temperature, and inlet velocity conditions. The predictions also indicate that the wave peak height decreases with increasing surface tension and decreases with increasing inlet velocity. This has an effect on the heat transfer characteristics of the condensation process. The condensation heat transfer increases sharply by increasing the temperature difference between the wall and saturation temperature of the inlet steam. (Less)