Velocity, Temperature, and Concentration Fields on Laminar Forced Film Condensation of Vapour–Gas Mixture

Abstract

A series of treatments on concentration- and temperature-dependent physical properties are successfully treated for laminar forced film condensation of vapour–gas mixture. The physical property factors of liquid film are temperature-dependent. The physical property factors of vapour–gas mixture film are concentration-dependent in the governing similarity mathematical model; however, after the analysis, it is found that they cover the temperature-dependent physical property factors of vapour and gas. Obviously, the concentration-dependent physical properties of vapour–gas mixture are closely dependent on the temperature-dependent physical properties of vapour and gas. Finally, and a set of physical property factors of governing similarity mathematical models becomes functions of the dimensionless temperature and concentration for convenient numerical calculation. Seven interfacial matching conditions, such as those for two-dimensional velocity component balances, shear force balance, mass flow rate balance, temperature balance, heat transfer balance, concentration condition, as well as the balance between the condensate mass flow and vapour mass diffusion, are considered and rigorously satisfied in the numerical calculation. Take the laminar forced film condensation of water vapour–air mixture as an example of the condensation, a formulation for rigorous determination of the water vapour condensate saturated temperature with variation of the vapour partial pressure is applied for rigorous determination of interfacial vapour saturation temperature. By means of the provided iterative calculation procedure, interfacial vapour saturation temperature is evaluated finally. All these lead to rigorous and reliable numerical results on the laminar forced film condensation of vapour–gas mixture. A system of rigorous numerical results is obtained for laminar forced film condensation of water vapour–air mixture, including velocity, temperature and concentration fields of the two-phase film flows. It is found that the noncondensable gas strongly reduced the wall subcooled grade, because it strongly reduces the interfacial vapour saturation temperature. Increasing the wall temperatures t _w causes decreasing the condensate liquid film thickness obviously, increasing the wall temperature gradient obviously, and increasing the vapour–gas mixture film thickness at accelerative pace. Furthermore, increasing the bulk water vapour mass fraction $C_{mv,\infty}$causes increasing the condensate liquid film velocity and thickness obviously, decreasing the wall temperature gradient obviously, and increasing the vapour–gas mixture film thickness obviously. However, with increasing the wall temperature, the effect of the bulk vapour mass fraction on the two-phase film flows will decrease. The study results of this work for laminar forced film condensation from vapour–gas mixture is a basis on a successive investigation for its heat and mass transfer.