Convective condensation of vapor in the presence of a non-condensable gas of high concentration in laminar flow in a vertical pipe

Abstract

The problem of laminar film condensation of vapor in the presence of high concentration non-condensable gas such as humid air flowing in a vertical pipe under laminar forced convection conditions is formulated theoretically. The vapor condensing at dew point temperature releases both sensible and latent heats and diffuses on to the surface of the pipe through a non-condensable gas film. Thus it is treated as combined heat and mass transfer problem governed by mass, momentum and energy balance equations for the vapor–gas mixture and diffusion equation for the vapor species. The flow of the falling condensate film is governed by the momentum and energy balance equations. The temperature at the gas-to-liquid interface, at which the condensation takes place, is estimated with the help of the heat balance and mass balance equations at the interface. The local and average values of the condensation Nusselt number, condensate Reynolds number, gas–liquid interface temperature and pressure drop are estimated from the numerical results for different values of the system parameters at inlet, such as relative humidity, temperature of vapor–gas mixture, gas phase Reynolds number and total pressure. The gas phase convection Nusselt and Sherwood numbers are also computed from numerical results. The predictions of the present study are compared with the experimental data available in literature, and the agreement is found to be reasonably good. An implicit pressure correction method developed by the authors is used in solving the momentum balance equation for the gas phase.