Axial dispersion in coiled tubular reactors : The Effect of Curvature at Low Dean Numbers |
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Authors: | Denys F Leclerc Carr J Smith EClifford Toren |
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Institution: | Department of Pathology, University of South Alabama Medical Center, 2451 Fillingim Street, Mobile, AL 36617 U.S.A. |
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Abstract: | Deforming tubing (e.g., coiling) reduces axial dispersion in flow-injection systems and post-column reactors. An improvement is presented for a previous theoretical treatment of axial dispersion in coiled tubes. New experimental data are also presented for different coil radii. Changes were necessary because smaller-than-predicted dispersion improvements were observed. This contradicts earlier treatments that predict a linear dependence on the aspect ratio of the coil. Evidence is presented that this is explained by assuming a boundary layer thickness much smaller than the radius of the tube and proportional to the ratio of radial velocities. This is a special case of earlier theory and it predicts an almost curvature-independent change in dispersion. The inclusion of the critical Reynolds number, Rec, to form a reduced parameter, (Re/Rec), accounts for all observations, including some previously-defined empirical constants. The dispersion is found to increase as (Re/Rec)2/3Sc at low fluid velocities and to decrease as (Re1/6c/(Re/Rec)4/3Sc0.08) at higher velocities. Experiments are reported for several coil radii and with a range of proteins and protein mixtures. |
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