CFD-DEM Modeling of Laboratory-Scale Fluidized BED Containing Binary Mixtures: Validation with Radioactive Particle Tracking (RPT) Experiments

Gas-fluidized beds are extensively utilized in industrial processes owing to the fact that these systems offer advantages like uniform particle mixing, possibility to operate in continuous state, uniform temperature gradients. Due to complex hydrodynamics and lack of complete understanding of these systems, accurate scale-up of such units is challenging. Therefore, gaining more insights into the complex hydrodynamics is of utmost importance and this can be achieved through development and validation of underlying hydrodynamic models. Euler–Lagrange model/ Discrete Particle Model arguably gives more physically realistic results, as this method is based on the tracing of each particle inside the system. The present study seeks to capture these complicated flow patterns at various conditions using Euler-Lagrange approach.

CFD-DEM simulation of a laboratory-scale 3D binary fluidized bed has been carried out consisting of glass beads of 0.5- and 2-mm diameter particle sizes. To determine the contact forces between particles, Hertzian model was used. Effect of bed composition was checked on overall hydrodynamics of the system by varying the coarser particle fraction from 10 – 40% at different superficial gas velocities. Effect of different drag models like Gidaspow, Di Felice and Koch-Hill were also observed in the simulations. For validation of the efficacy of the simulations, a direct comparison is made of the results obtained, i.e., minimum fluidization velocity, time averaged axial mean velocity and RMS velocity of solid, with an experimental technique that is Lagrangian in nature, viz. Radioactive Particle Tracking (Roy et al., 2021). The observations from simulation include not only comparisons of the mean profiles, but also the fluctuating components of velocity from the flotsam and jetsam phases. As the bed consists of a distribution of particle sizes, the mixing pattern of the polydisperse bed is also studied.

Keywords: Computational Fluid Dynamics, Discrete Element Model, Binary Fluidized Bed, Radioactive Particle Tracking