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Abstract
The additivity assumption underlying Giddings' coupling model for the eddydispersion in laminar flows through heterogeneous media is critically analyzed and a potential solution for its nonadditivity in the high velocity limit is presented. Whereas the unit cell in Giddings' model only consists of a single velocity bias step, the unit dispersion cell of the newly proposed model comprises two consecutive velocity bias steps. Consequently, the unit cell of this new model allows to account for the occurrence of an internal velocity bias rectification at high reduced velocities and is therefore additive in both the low and high velocity limit.
First, a mathematical expression for the velocity and diffusiondependency of the model's dispersion characteristics has been established. Subsequently, the physical behavior of the model is discussed. It is shown the relation between the eddydispersion plate height h and the reduced velocity ν can be expected to display a local maximum in systems where the transversal dispersion purely occurs by molecular diffusion, as is the case in perfectly ordered flowthrough media. In disordered media, where the transversal dispersion also contains a significant advective component, the model predicts a velocitydependency that is qualitatively similar to that described by Giddings' coupling model but, all other conditions being equal, converges to a significantly smaller horizontal asymptote at high reduced velocity. The latter might shed new light on earlier eddydispersion studies pursuing a quantitative agreement between experimental data and the Giddings model.
First, a mathematical expression for the velocity and diffusiondependency of the model's dispersion characteristics has been established. Subsequently, the physical behavior of the model is discussed. It is shown the relation between the eddydispersion plate height h and the reduced velocity ν can be expected to display a local maximum in systems where the transversal dispersion purely occurs by molecular diffusion, as is the case in perfectly ordered flowthrough media. In disordered media, where the transversal dispersion also contains a significant advective component, the model predicts a velocitydependency that is qualitatively similar to that described by Giddings' coupling model but, all other conditions being equal, converges to a significantly smaller horizontal asymptote at high reduced velocity. The latter might shed new light on earlier eddydispersion studies pursuing a quantitative agreement between experimental data and the Giddings model.
Original language  English 

Article number  461195 
Number of pages  10 
Journal  Journal of Chromatography. A 
Volume  1624 
Publication status  Published  2 Aug 2020 
Keywords
 Eddydispersion
 Modelling
 Band broadening
 Packed bed
 Column Technology
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SRP6: Strategic Research Programme: Exploiting the Advantages of Order and Geometrical Structure for a Greener Chemistry
Desmet, G., Denayer, J., Denayer, J., Desmet, G. & Denayer, J.
1/11/12 → 31/10/22
Project: Fundamental