(474c) A Novel Approach to Simulate Large-Scale Fluidized Beds By CFD-DEM

Coupling of
Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) is a recently
developed approach for the modelling of particulate flows, such as fluidized
bed, pneumatic conveying and cyclones. However, this approach suffers from
several shortcomings, including the need for highly calibrated drag laws of
particles (and swarms), the modeling of turbulence dampening/generation by
particles and the need for collisional models that account accurately for
enduring and short contacts. Moreover, the number of simulated particles is
restricted due to the extremely high computational time. Consequently, in this
study, we attempt to analyze a methodology to reduce the computational cost by
replacing the original particles with larger particles (decreasing the particle
number) while the characteristic dimensionless groups are kept constant for
both scaled and base cases. In other words, replacing original particles with
larger particles enables us to decrease the computational cost while having the
similar hydrodynamic behavior for both base and scaled cases. The dimensionless
numbers (groups) which are kept similar in both base and scaled simulations are
particle Reynolds number (Re), particle Froude number (Fr), particle to fluid
density ratio, bed-to-particle diameter ratio and bed-width to initial
bed-height ratio. The dynamic behavior of a fluidized bed for both, base case
and scaled case, is also analyzed to determine the significance of each
dimensionless number.

In the current study, our
high-performance GPU code XPS coupled with an CFD code is used. The adequacy of
the proposed methodology is tested on a pseudo 2D single-spout fluidized bed.
The setup under investigation was previously used to validate the coupled
CFD-DEM code [1]. To check the hydrodynamic similarity the
instantaneous solid volume fraction, instantaneous gas phase velocity and time-averaged
particle velocity at different locations of the fluidized beds are compared
between the base and scaled cases. A typical comparison of the instantaneous
gas velocities between base and scaled cases is presented in Figure 1.

The simulation results showed that similar dynamics can be
obtained for both base and scaled cases, proving that the proposed method may
be applied to simulate the large-scale fluidized beds with a reasonable
computational time.

Reference:

[1] D. Jajcevic, E. Siegmann, C. Radeke, J.G.
Khinast, Large-scale CFD?DEM simulations of fluidized granular systems,
Chemical Engineering Science, 98 (2013) 298-310.