Convective Condensation of Vapor in Laminar Flow in a Vertical Parallel Plate Channel in the Presence of a High-Concentration Noncondensable Gas

Abstract

The problem of laminar film condensation of a vapor from vapor-gas mixture in laminar flow in a vertical parallel plate channel is formulated theoretically. The flowing gas-vapor mixture contains a noncondensable gas in high concentration. An example of this case is the flow of humid air, in which air is present in high concentration. Vapor condenses at the dew point temperature corresponding to mass fraction of vapor in the gas-vapor mixture and the total pressure. The rate of condensation is controlled by the diffusion of the vapor through the noncondensable gas film. Thus the problem of convective condensation is treated as a combined problem of heat and mass transfer. The problem is governed by the mass, momentum and energy balance equations for the vapor-gas mixture flowing in a channel, and the diffusion equation for the vapor species. The flow of the falling film of condensate is governed by the momentum and energy balance equations for the condensate film. The boundary conditions for the gas phase and the condensate film are considered. The temperature at the gas-to-liquid interface is estimated by making use of the equations of heat and mass balance at the interface. The local condensation Nusselt number, condensation Reynolds number, and temperature at the gas-to-liquid interface are estimated from the numerical results for different values of the system parameters at the channel inlet, such as relative humidity, temperature of vapor-gas mixture, gas phase Reynolds number, and total pressure. The condensation heat transfer coefficients computed from the present theory are compared with the experimental data available in literature, and the agreement is found to be good. The present work is an extension of the earlier work, in which the problem of in-duct condensation of humid air in turbulent flow was solved theoretically. Humid air is considered as the gas-vapor mixture, since various physical and thermal properties have to be specified during the analysis.