“…The drag force is considerably influenced by the drag coefficient . This coefficient is related to the Reynolds number of the particles, which takes into account the superficial velocity differences between particles and the surrounding fluid [ 33 , 34 ]: where, is the dynamic viscosity of the fluid. The influence of the particle concentration in a mesh cell on the drag force in Equation (5) is modeled with a function [ 32 ]: …”
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.
“…The drag force is considerably influenced by the drag coefficient . This coefficient is related to the Reynolds number of the particles, which takes into account the superficial velocity differences between particles and the surrounding fluid [ 33 , 34 ]: where, is the dynamic viscosity of the fluid. The influence of the particle concentration in a mesh cell on the drag force in Equation (5) is modeled with a function [ 32 ]: …”
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.
“…According to Wen and Yu [50], the minimum fluidization velocity of spheres of equal volume was about 0.91 m s -1 . Similar to our previous works [5,51], we used different experimental setups to obtain the particle properties needed for the contact model in DEM. In order to determine the Young's modulus and the coefficient of restitution, a Nanoindenter (Hysitron TI Premier, Bruker Corporation) was used.…”
Dedicated to Prof. Dr.-Ing. Joachim Werther on the occasion of his 80th birthdayThe fluidization behavior of cylindrical particles in a spouted bed was first investigated experimentally using a camera setup. The obtained average spouted bed height was used to evaluate the accuracy of different drag models in CFD-DEM simulations with the superquadric approach to model the particle shape. The drag model according to Sanjeevi et al. showed the best agreement. With this model, cylindrical particles were simulated in a rotor granulator and the particle dynamics were compared with the fluidization of volume equivalent spherical particles.
“…Using DEM-CFD models based on comprehensive material characterization of lactose powders, Hesse et al [ 34 ] showed that the vertical pressure gradient is significantly impacted by the horizontal airflow, and thereby the discharge rates can be different from expectation (Fig. 4 ).…”
Section: Modeling Of Batch Processesmentioning
confidence: 99%
“… Fig. 4 Relative airflow (arrows), air pressure (left half), and absolute particle velocity (right half) at steady state for varying hopper angles from CFD-DEM simulations; dead zones (particle velocity < 4 cm/s) are emphasized [ 34 ] …”
Most challenges during the development of solid dosage forms are related to the impact of any variations in raw material properties, batch size, or equipment scales on the product quality and the control of the manufacturing process. With the ever pertinent restrictions on time and resource availability versus heightened expectations to develop, optimize, and troubleshoot manufacturing processes, targeted and robust science-based process modeling platforms are essential. This review focuses on the modeling of unit operations and practices involved in batch manufacturing of solid dosage forms by direct compaction. An effort is made to highlight the key advances in the past five years, and to propose potentially beneficial future study directions.
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