Compaction and dilation rate dependence of stresses in gas-fluidized beds

TL;DR

This study uses a hybrid particle and gas dynamics model to analyze stresses in gas-fluidized beds, revealing significant path dependence in solid phase variables during dilation and compaction, which challenges existing kinetic theory models.

Contribution

It demonstrates the existence of path dependence in solid phase variables in fluidized beds, highlighting the need for new constitutive models that account for large dilation and compaction rates.

Findings

Solid phase variables show path dependence during waves.

Kinetic theory models do not capture this path dependence.

Path dependence occurs in both cohesive and non-cohesive particle 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.