DEM numerical investigation of wet particle flow behaviors in multiple-spout fluidized beds

Effects of Particle Diameter and Inlet Flow Rate on Gas-Solid Flow Patterns of Fluidized Bed

The complex multiscale characteristics of particle flow are notoriously difficult to predict. In this study, the evolution process of bubbles and the variation of bed height were investigated by conducting high-speed photographic experiments to verify the reliability of numerical simulations. The gas-solid flow characteristics of bubbling fluidized beds with different particle diameters and inlet flow rates were systematically investigated by coupling computational fluid dynamics (CFD) and discrete element method (DEM). The results show that the fluidization in the fluidized bed will change from bubbling fluidization to turbulent fluidization and finally to slugging fluidization, and the conversion process is related to the particle diameter and inlet flow rate. The characteristic peak is positively correlated with the inlet flow rate, but the frequency corresponding to the characteristic peak is constant. The time required for the Lacey mixing index (LMI) to reach 0.75 decreases with increasing inlet flow rate; at the same diameter, the inlet flow rate is positively correlated with the peak of the average transient velocity; and as the diameter increases, the distribution of the average transient velocity curve changes from "M" to linear. The results of the study can provide theoretical guidance for particle flow characteristics in biomass fluidized beds.

Numerical Investigation of the Particle Dynamics in a Rotorgranulator Depending on the Properties of the Coating Liquid

In the pharmaceutical industry, the coating of particles is a widely used technique to obtain desired surface modifications of the final product, e.g., controlled release of the active agents. The production of round, coated particles is particularly important, which is why fluidized bed rotor granulators (FBRG) are often used for this process. In this work, Computational Fluid Dynamics (CFD) coupled with the Discrete Element Method (DEM) is used to investigate the wet particle dynamics, depending on the properties of the coating liquid in a FBRG. The DEM contact model was extended by liquid bridge model to account for capillary and viscous forces during wet contact of particles. The influence of the relative contact velocity on the maximum length of the liquid bridge is also considered in the model. Five different cases were compared, in which the particles were initially wetted, and the liquid loading as well as the surface tension and viscosity of the liquid were changed. The results show that increasing viscosity leads to a denser particle bed and a significant decrease in particle rotational velocities and particle motion in the poloidal plane of the FBRG. Reducing the liquid loading and surface tension results in increased particle movement.

Computational Modeling of Fluidized Beds with a Focus on Pharmaceutical Applications: A Review

The fluidized bed is an essential and standard equipment in the field of process development. It has a wide application in various areas and has been extensively studied. This review paper aims to discuss computational modeling of a fluidized bed with a focus on pharmaceutical applications. Eulerian, Lagrangian, and combined Eulerian-Lagrangian models have been studied for fluid bed applications with the rise of modeling capabilities. Such models assist in optimizing the process parameters and expedite the process development cycle. This paper discusses the background of modeling and then summarizes research papers relevant to pharmaceutical unit operations.

Comparison of Euler-Euler and Euler-Lagrange Approaches for Simulating Gas-Solid Flows in a Multiple-Spouted Bed

In this work, a comparative study of Euler-Euler and Euler-Lagrange approaches for modeling gas-solid flows in the multiple-spouted bed has been carried out to investigate the hydrodynamics of gas-solid flows. The influence of inlet gas velocity on the hydrodynamics of gas-solid flows in the multiple-spouted bed is investigated as well. Hydrodynamic characteristics of gas-solid flows such as flow behaviors, solid volume fraction, particle velocity and particle trajectory are analyzed and discussed in detail, providing some basic mechanism analysis of the gas-solids in the multiple-spouted bed. It is found that the central spout gas jet is a little confined by the auxiliary gas jets, and the hole-to-hole synergy is quite obvious when the auxiliary spout gas velocity is higher than the central spout gas velocity. When central/auxiliary gas velocity is 10/20 m/s, the maximum vertical particle velocities predicted by Euler-Euler and Euler-Lagrange approaches are 452 mm/s and 721 mm/s at the height of 10 mm respectively. A typical cycle period of a single particle is about 1.25 s, and the residence time in the spout regions is about 0.14 s in one cycle period in auxiliary dominant pattern. The curves of bed expansion height versus time calculated by Euler-Lagrange approach rise and fall periodically, while the curves calculated by Euler-Euler approach keep steady with little change. It is much easier for particles to be blew in the multiple-spouted bed using the Euler-Lagrange approach. The simulation results obtained from two models can provide some guidance for modifying the multiple-spouted bed to optimize physical operations such as drying and coating in the multiple-spouted bed.