A Generalized Diffusion Layer Model for Condensation of Vapor With Noncondensable Gases

Abstract

The diffusion layer model for condensation heat transfer of vapor with noncondensable gases was originally derived on a molar basis and developed from an approximate formulation of mass diffusion, by neglecting the effect of variable vapor–gas mixture molecular weights across the diffusion layer on mass diffusion. This is valid for gases having a molecular weight close to that of the vapor or for low vapor mass transfer rates, but it may cause serious error if a large gradient in the gas concentration exists across the diffusion layer. The analysis herein shows that, from the kinetic theory of gases, Fick’s law of diffusion is more appropriately expressed on a mass basis than on a molar basis. Then a generalized diffusion layer model is derived on a mass basis with an exact formulation of mass diffusion. The generalized model considers the effect of variable mixture molecular weights across the diffusion layer on mass diffusion and fog formation effects on sensible heat. The new model outperforms the one developed by Peterson when comparing with a wide-ranging experimental database. Under certain limiting conditions, the generalized model reduces to the one developed by Peterson.

Transition from natural to mixed convection for steam–gas flow condensing along a vertical plate

“…9. This is of practical importance to the heat and mass transfer analogy approach in engineering calculations, where a convection-regime dependent correlation must be decided [27]. In contrast to Fig.…”

Review of vapor condensation heat and mass transfer in the presence of non-condensable gas

“…Liao and Vierow et al [137,138] and Hogan et al [139] then expanded the diffusion layer model to the generalized diffusion layer model. They proposed that, from the kinetic theory of gases, Fick's law of diffusion was more appropriately expressed on a mass basis than on a molar basis; they also 9.…”

Condensation of a hydrocarbon in the presence of a non-condensable gas: Heat and mass transfer

“…Authors presented three different correlations, implementing the degradation factor method, diffusion layer theory, and the mass transfer conductance model. Liao and Vierow [13] indicated that the original diffusion model is valid for gases having a molecular weight close to that of the vapor or low vapor mass transfer rates, but serious error may arise if a large gradient in the gas concentration exists across the diffusion layer. The authors presented a generalized model which included the effect of variable mixture molecular weights across the diffusion layer on mass diffusion and the effect of fog formation on the sensible heat.…”

“…A theoretical model was developed based on Liao's modified diffusion layer theory [13] including the roughness and the suction effect. The predicted values agreed well with their experimental and literature data.…”