Article

Film‐penetration model for mass and heat transfer

Carnegie Institute of Technology, Pittsburgh, Pennsylvania
AIChE Journal (Impact Factor: 2.49). 06/2004; 4(1):97 - 101. DOI:10.1002/aic.690040118
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    ABSTRACT: A theoretical analysis using the surface-renewal and film-penetration models, which includes gas-phase resistance to mass transfer, is presented for the rate of absorption of a gas and its transfer to the bulk liquid in the case where the solute gas undergoes a first-order chemical reaction in the liquid phase. It reveals that: (a) The fraction of absorbed gas transported to the bulk liquid depends upon the Hatta number Ha in case of the surface-renewal model and on Ha as well as a dimensionless hydrodynamic parameter in case of the film-penetration model. (b) The widely assumed law of addition of resistances is valid for the surface-renewal and film-penetration models. (c) The reaction influences both the overall mass-transfer coefficient and the nature of the driving force, i.e. the increased rate of absorption due to the reaction is not solely due to the enhancement factor multiplying the liquid-phase mass-transfer coefficient for physical absorption as has been conventionally assumed in the literature. It is also shown that in a gas-liquid reactor the film and surface-renewal models give close predictions for both the rate of absorption and concentration of dissolved gas in the liquid leaving the reactor. For values of Ha ≥ 0.5, the bulk-liquid concentration of dissolved gas predicted by both models is negligible compared to its interfacial concentration.
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    ABSTRACT: The aim of this study is to quantify the mass transfer velocity using turbulence parameters from simultaneous measurements of oxygen concentration fields and velocity fields. The surface divergence model was considered in more detail, using data obtained for the lower range of β (surface divergence). It is shown that the existing models that use the divergence concept furnish good predictions for the transfer velocity also for low values of β, in the range of this study. Additionally, traditional conceptual models, such as the film model, the penetration-renewal model, and the large eddy model, were tested using the simultaneous information of concentration and velocity fields. It is shown that the film and the surface divergence models predicted the mass transfer velocity for all the range of the equipment Reynolds number used here. The velocity measurements showed viscosity effects close to the surface, which indicates that the surface was contaminated with some surfactant. Considering the results, this contamination can be considered slight for the mass transfer predictions. © 2009 American Institute of Chemical Engineers AIChE J, 2010
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H. L. Toor