Drag on two nonuniformly structured flocs moving along the axis of a cylindrical tube |
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Authors: | Jyh-Ping Hsu Shu-Jen Yeh Shiojenn Tseng |
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Institution: | (1) Department of Chemical Engineering, National Taiwan University, 10617 Taipei, Taiwan;(2) Department of Mathematics, Tamkang University, Tamsui, 25137 Taipei, Taiwan |
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Abstract: | The boundary effect on the drag on two identical, nonuniformly structured flocs moving along the axis of a cylindrical tube
filled with a Newtonian fluid is investigated at a small to medium larger Reynolds number. A two-layer model is adopted to
simulate various possible structures of a floc, and the flow field inside is described by Darcy–Brinkman model. The results
of numerical simulation reveal that a convective flow is present in the rear region of a floc when Reynolds number is on the
order of 40. The presence of the tube wall and/or the porous structure of a floc has the effect of reducing that convective
flow. For a fixed level of the volume-average permeability of a floc, the influence of the tube wall on the drag depends upon
floc structure; the influence on a nonuniformly structured floc is more significant than that on a uniformly structured floc.
The more nonuniform the floc structure, the more appreciable the deviation of the drag coefficient–Reynolds number curve from
a Stokes’-law-like relation becomes. The smaller the volume-average permeability of a floc and/or the smaller the separation
distance between the two flocs, the greater is the deviation, but the presence of the tube wall has the effect of reducing
that deviation. |
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Keywords: | Drag on two flocs Nonuniformly structured Boundary effect Flocs in cylindrical tube |
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