A fundamental understanding of the relevant heat and mass transfer processes is necessary to further improve, from a theoretical basis, the design of condensing heat exchangers. The objective was to develop an experimentally supported mathematical model of vapor condensation from a mixture of noncondensable gas and vapor. The model was obtained from an analytically derived, exact, explicit, two-dimensional solution to the concentration boundary-layer equation. Both boundary-layer and fully developed flow in a channel were considered. Included in the model was an experimentally obtained diffusion inhibition correlation.;Water vapor concentration and temperature profiles of humid air were measured over a cooled fin model at velocities typical of a dehumidifying heat exchanger. A wet-bulb concentration probe was developed to make these measurements. A three-dimensional finite element analysis of velocity and temperature further reconciled experimental measurements and model predictions. The experimental data supports an inhibited diffusion hypothesis. The hypothesis defines a relationship between the degree of diffusion inhibition and Reynolds number. Explanations of this relationship, based on boundary-layer gradients, are postulated.;Exchanger sensible heat ratio was found to increase with increasing inlet velocity, mainly due to increasing inhibition of diffusion. Using the finite element model and smoke visualization, it was confirmed that buoyancy induced convection currents disturb the laminar boundary layer, increasing heat and mass transfer. A noncondensable gas film was detected which decreases in thickness with increasing inlet velocity or diffusion resistance.;It was concluded that condensation rate is related to the gradient across the noncondensable film and the effective mass diffusivity of the vapor-gas mixture. It appears that the concentration gradient near the interface may be a strong function of gas film thickness. Condensation rate may be significantly increased by increasing the diffusion rate through the boundary layer or decreasing the gas film thickness.
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