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