(139d) An Integrated Workflow for Numerical Generation and Meshing of Packed Beds of Non-Spherical Particles

An
integrated workflow for numerical generation and meshing of packed beds of
non-spherical particles

Behnam Partopour, Anthony G. Dixon

Department of Chemical Engineering,
Worcester Polytechnic Institute,

Worcester, MA, USA, 01609

            Packed
beds are widely used in different areas of the chemical industry such as
reaction engineering and separation processes, and researchers from different
disciplines such as chemical and mechanical engineering and material science
are interested in studying them. Therefore, along with experimental methods, the
numerical generation of these beds is extensively investigated. Unlike packed
beds of spherical particles, the contacts between non-spherical particles could
include lines and surfaces. Therefore, collision detection and subsequent
meshing in those areas can computationally be challenging.

In this work we introduce the automated
packed bed generator (PBG) package for spherical and non-spherical particles
based on the Bullet physics library. The library includes a robust collision
detection module which uses the impulse based collision detection method¹.
The package gets the user input for parameters such as shape, dimensions and
number of particles, as well as friction and restitution factors, etc., and
returns an STL file of the constructed geometry along with the bed properties
(e.g. void fraction and angle distributions).

The constructed packed bed STL file
then is imported to meshing software and a 3-dimensional mesh is generated
based on the shrink-wrap method. The bed properties for packed beds of
different shapes of particles are validated against existing experimental and
computational data in the literature. The meshed geometries are imported to CFD
software, and momentum and heat transfer simulations are carried out. Velocity
and temperature profiles are validated against the experimental data, and
previous CFD simulations, respectively. The package has shown to have two
important advantages over similar tools such as the Discrete Element Method
(DEM). First, the PBG simulation time is significantly lower than DEM tools (~1
hour for a packed bed of 1500 particles). Second, Bullet physics uses direct
mesh representations of the original objects to detect the collisions and
contact points while DEM tools use multi-spherical approximate shapes to detect
the contact points and then replace them by the original representations of the
particles (e.g. cylinders or rings). Several studies have raised concerns about
the accuracy as well as computational cost of such methods^{2, 3}.
Finally, for the first time the generated and meshed geometries are
successfully used for resolved particle fixed bed CFD simulations.

References

1- Pytlos M, Gilbert M, Smith CC. Modelling granular soil
behaviour using a physics engine. Géotechnique
Letters 2015; 5:243–249

2-
Marigo M, Stitt EH. Discrete element
method (DEM) for industrial applications: 
comments on calibration and validation for the modelling of cylindrical pellets,
KONA Powder & Particle J 2015;
32:236-252.

3- Guo Y, Wassgren
C, Ketterhagen W, Hancock B, Curtis J. Some
computational considerations associated with discrete element modeling of
cylindrical particles. Powder Technol 2012; 228;193–198.