## Fluidization by lift of 300 circular particles in plane Poiseuille flow by
direct numerical simulation

*H.G. Choi and Daniel D. Joseph*

#### Abstract

We study the transport of a slurry of heavier than liquid circular particles
in a plane pressure driven flow in a direct simulation. The flow is calculated
in a periodic domain containing 300 circular particles. The study leads to the
concept of fluidization by lift in which all the particles are suspended by
lift forces against gravity perpendicular to the flow. The study is framed as
an initial value problem in which a closely packed cubic array of particles
resting on the bottom of the channel are lifted into suspension. All the
details of the flow are resolved numerically without model assumptions. The
fluidization of circular particles first involves bed inflation in which liquid
is driven into the bed by high pressure at the front and low pressure at the
back of each circle in the top row. This kind of bed inflation occurs even at
very low Reynolds numbers but it takes more time for the bed to inflate as the
Reynolds number is reduced. It appears that the bed will not inflate if the
shear Reynolds number is below the critical value for single particle lift-off.
The flows with a single particle are completely determined by a shear Reynolds
number and a gravity parameter when the density ratio and aspect ratio
parameters are specified. In the multi particle case the volume fraction and
distribution also matters. The transition to a fully fluidized slurry by waves
is discussed.

An analytical model of the steady motion of a single particle dragged
forward in a Poiseuille flow is derived and compared with a simulation. The
undisturbed fluid velocity is always larger than the particle velocity
producing a fluid hold-up. The effect of the hold-up in the many particle case
is to greatly reduce the velocity of the mixture which may be described by a
two-fluid model in which the solid laden mixture is regarded as a second fluid
with effective properties.

Download PDF files,
Part-A
Part B.

February 2000. Contact H.G. Choi
for questions about this article.

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*Last Modified: Friday, 07-Dec-2001 13:00:17 CST*