Numerical Solution For Vapor Condensation In The Presence Of Noncondensable Gas

This thesis aims to study condensation heat transfer in the presence of a noncondensable gas. Different models are proposed for condensation on a vertical surface and in condensers, respectively.First, numerical two-phase flow model for laminar film condensation with a noncondensable gas on vertical surface is developed. The full boundary layer model consists of mass, momentum, energy and species (mixture only) conservation equations for both the liquid and vapor-gas mixture. Apply a finite control volume method to disperse the partial differential equations, which were transformed to a new coordinate system. Calling REFPROP software to evaluate the local fluid properties, numerical results are obtained by using TDMA to solve discrete equations. The liquid film thickness and the effect of air content on condensation are presented as results.Second, numerical single-phase flow model for laminar film condensation with a noncondensable gas on vertical surface is developed. Neglecting the impact of liquid film on flow field, and assuming that vapor condensation only happens in the computational cell adjacent to the wall, the condensation model is carried out with ANSYS FLUENT by means of user-defined functions (UDF). Simulation results are in good agreement with those are solved by the two phase model, which proves the feasibility of single phase flow model.Last, numerical single-phase flow model for laminar film condensation with a noncondensable gas in condenser is developed. The porous media method is employed to model the presence of tube bundles in the condenser. The effect of tubes on flow field is reflected by distributed resistance with adding source to momentum equations. The condensation heat transfer coefficient is obtained by computing the thermal resistances from tube side cooling water to the shell side vapor-air mixture. The condensation is realized with adding the mass source to continuity equation. All of noncondensable gas and remaining vapor are extracted by vent as mass sink. After numerical calculating the experimental condenser to check the accuracy of the model results due to comparison with experimental data, the industrial condenser simulation is implemented, followed by heat transfer analysis.