Fully Coupled Elliptic Numerical Model for Film Condensation From Vapour-Gas Mixtures in Vertical Parallel Plate Channels

Abstract

Laminar film condensation is an important phenomenon which occurs in numerous industrial applications such as refrigeration, chemical processing, and thermal power generation industries. It is well known that film condensation heat transfer is greatly reduced in the presence of a non-condensing gas. The present work performs a numerical analysis of the steady-state, laminar film condensation from a vapour-gas mixture in vertical parallel plate channels to demonstrate a computer model that could assist engineering analysts designing systems involving these phenomena. The present model has three new aspects relative to other current work. First, the complete elliptic two-dimensional governing equations are solved in both phases. Thus, the entire channel domain is solved rather than using an approach that marches along the channel from inlet to a prescribed length. Second, a dynamically determined sharp interface is used between the phases. This sharp interface is determined during the solution on a non-orthogonal structured mesh. Third, the governing equations are solved in a fully-coupled approach. The equations for two velocities, pressure, temperature, and gas mass fraction are solved in a coupled method simultaneously for both phases. Discretisation has been done based on a finite volume method and a co-located variable storage scheme. An in-house computer code was developed to implement the numerical solution scheme. Detailed results are presented for laminar film condensation from steam-air mixtures flowing in vertical parallel-plate channels. The results include velocity and pressure profiles, as well as axial variations of film thickness, Nusselt number and interface gas mass fraction. Detailed comparisons are made with results from a parabolic solution approach.