An Integrated Workflow for Numerical Generation and Meshing of Packed Beds of Non-Spherical Particles: Applications in Chemical Reaction Engineering

An integrated workflow for numerical generation and meshing of packed beds of non-spherical particles: Applications in chemical reaction engineering

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.In particular, packed bed models are needed where different particle shapes are used to fill low tube-to-particle diameter ratio (N) beds. 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, see first figure).

             

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. Finally, for the first time the generated and meshed geometries are successfully used for resolved particle fixed bed CFD simulations. An ethylene epoxidation reaction mechanism² is coupled to three-dimensional CFD simulations of randomly packed bed of spheres, Raschig rings, and quadrilobes. Ethylene mass fraction gradients on the surface of the quadrilobe particles as well as velocity contours are shown in the second figure.

References

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

2- Linic S, Barteau MA. Construction of a reaction coordinate and a microkinetic model for ethylene epoxidation on silver from DT calculations and surface science experiments. J. Catal. 2003; 214:200-2012