Compaction
and dilation rate dependence of stresses in gas-fluidized beds
Abstract:
A particle dynamics-based hybrid model, consisting of monodisperse
spherical solid particles and volume-averaged gas hydrodynamics, is used
to study traveling planar waves (one-dimensional traveling waves) of
voids formed in gas-fluidized beds of narrow cross sectional areas.
Through ensemble-averaging in a co-traveling frame, we compute solid
phase continuum variables (local volume fraction, average velocity,
stress tensor, and granular temperature) across the waves, and examine
the relations among them. We probe the consistency between such
computationally obtained relations and constitutive models in the
kinetic theory for granular materials which are widely used in the
two-fluid modeling approach to fluidized beds. We demonstrate that solid
phase continuum variables exhibit appreciable ``path dependence'',
which is not captured by the commonly used kinetic theory-based models.
We show that this path dependence is associated with the large rates of
dilation and compaction that occur in the wave. We also examine the
relations among solid phase continuum variables in beds of cohesive
particles, which yield the same path dependence. Our results both for
beds of cohesive and non-cohesive particles suggest that path-dependent
constitutive models need to be developed.
submitted
to Physics of Fluids, (2006); http://arxiv.org/abs/cond-mat/0602156
Manuscript available in PDF and PS formats.