Observations of axisymmetric tracer particle orientation during flow through a dilute fixed bed of fibers

  • Paul L. Frattini
    Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
  • Eric S. G. Shaqfeh
    Department of Chemical Engineering, Stanford University, Stanford, California 94305
  • Jeffrey L. Levy
    Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
  • Donald L. Koch
    School of Chemical Engineering, Cornell University, Ithaca, New York 14853

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<jats:p>Direct microstructural evidence for net tracer particle orientation induced solely by hydrodynamic interactions in a dilute, disordered, fibrous media is reported. A dilute fixed bed of randomly placed fibers was constructed and glycerol/water suspensions of either synthetic akaganeite (βFeOOH, average aspect ratio 6.3) or hematite (αFe2O3, average aspect ratio 1.6) tracer particles were made to flow axially through the bed at prescribed flow rates. Conservative linear dichroism, a noninvasive light scattering technique, was employed to provide a direct measure of the orientational order parameter for the tracer particle population at the end of the bed. The effect of Brownian motion on the hydrodynamically induced order in the suspensions was studied over three orders of magnitude in scaled rotary Peclet number, 5&lt;P&lt;2000. The steady degree of particle alignment exhibited by each suspension as it exited the fiber bed was found to be in good quantitative agreement with theory [Phys. Fluids 31, 728 (1988); ibid. 31, 2769 (1988)]. Time scales characterizing the development of net order induced in the tracer populations were investigated and compared qualitatively to theoretically derived bounds.</jats:p>

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