(740c) Oscillatory Flow Behavior in Vertical Riser Flow Simulations

Oscillatory flow
behavior in vertical riser flow simulations

Xiaokang Yan^*,
William Holloway, Sankaran Sundaresan

Department of
Chemical and Biological Engineering, Princeton University, Princeton, NJ

      A time-dependent quasi-periodic flow
behavior is observed in kinetic theory based two-fluid model simulations of
gas-particle flows in vertical risers.  Simulations were carried out in both 2D channels and
3D cylinders invoking
periodic boundary conditions in the axial direction and Johnson-Jackson[1] boundary conditions at the confining walls. Regular oscillations in the particle volume fraction
profile were observed,
manifested as
oscillatory flow patterns in 2D channel flow simulations and swirling patterns
in simulations performed in 3D
cylindrical geometries.
Oscillatory flow patterns of this type have
been reported in the
literature by Benyahia and coworkers using quasi-1D simulations [2, 3]. Simulations performed with different grid resolutions and flow
conditions in this work
confirmed that oscillations in both 2D and 3D axially periodic
simulations are robust. The period of the oscillations in 2D channels are found to depend primarily on the
particle Froude number, volume fraction, and channel width. This
spinning flow behavior is shown to provide an additional mechanism for
particle migration towards the wall that cannot be adequately captured in 2D
axisymmetric flow simulations.

References

1.      Johnson, P.C. and R. Jackson, Frictional collisional
constitutive relations for granular materials, with application to plane
shearing. J. Fluid Mech., 1987. 176: p. 67-93.

2.      Benyahia, S., A time-averaged model
for gas-solids flow in a one-dimensional vertical channel. Chem. Eng. Sci.,
2008. 63(9): p. 2536-2547.

3.      Benyahia, S., M. Syamlal, and T.J.
O'Brien, Study of the ability of multiphase continuum models to predict
core-annulus flow. AIChE J., 2007. 53(10): p. 2549-2568.

^*From School of Chemical
Engineering, China University of
Mining and Technology, Xuzhou, China