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Item type:Publication, Access status: with files , Numerical investigation of the particle dynamics in a rotorgranulator depending on the properties of the coating liquid(Multidisciplinary Digital Publishing Institute (MDPI), 2023-01-31); ; 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.Publicationtype: Journal ArticleScopus© Citations 1 29 239 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , CFD-DEM simulation of superquadric cylindrical particles in a spouted bed and a rotor granulator(Wiley-VCH, 2023-01); ; ; ; The 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.Publicationtype: Journal ArticleScopus© Citations 4 30 52 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Workshop GRK 2462 "Processes in Natural and Technical Particle-Fluid-Systems" (PintPFS) : 26th & 27th of September 2022, Hamburg, Germany : conference proceedings(2022-09-26); ; ; ; In the framework of Research Training Group GRK 2462 “Processes in Natural and Technical Particle-Fluid-Systems” (PintPFS), funded by the German Research Foundation (DFG), researchers from the fields of civil engineering, mechanical engineering, process engineering, and materials sciences investigate natural and technical Particle-Fluid-Systems (PFS) in an interdisciplinary approach. As PFS are ubiquitous in everyday life and relevant for many processes in industry, pharmacy, and food production, they represent a fascinating field of research with potential for promising and useful discoveries in many aspects.Publicationtype: Conference Proceedings408 2183 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigation of the influence of wetting on the particle dynamics in a fluidized bed rotor granulator by MPT measurements and CFD-DEM simulations(2022-08); ; ; In many processes, particles are coated or agglomerated. Thus, it is of considerable interest how liquid affects the particle dynamics. The production of round, coated pellets is particularly important in the pharmaceutical industry, which is why fluidized bed rotor granulators (FBRG) are often used for this process. In this work, the influence of liquid content on the particle dynamics in a FBRG was investigated experimentally by magnetic particle tracking measurements (MPT) and numerically using Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM coupling). A liquid bridge model was implemented in the DEM contact model to take the capillary and viscous forces during wet contact of particles into account. In addition, the model considers the influence of the relative contact velocity on the maximum liquid bridge length. In order to show that numerical simulations can correctly predict the particle dynamics in the process, the non-intrusive MPT technique was used for the continuous measurement of the particle position and orientation of a single tracer particle during experiments. Thus, the residence probability, the trajectories, as well as the translational and angular velocities of the particles were determined. The simulation results agree well with the experimental measurements.Publicationtype: Journal Article40 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigation of the influence of impact velocity and liquid bridge volume on the maximum liquid bridge length(2022-06); ; ; Several models exist to predict the capillary forces due to liquid bridges during static particle contacts. However, for dynamic impacts, there is still a lack of knowledge to accurately describe the geometry and rupture of liquid bridges. This is essential in order to calculate correctly the energy dissipation in numerical models. Therefore, the liquid bridge volume during the rebound phase of collision, the restitution coefficient, the rupture time and the maximum liquid bridge length were analyzed for a wide range of contact velocities from 0.0001 to 4.0 m∙s−1. To perform experiments at different velocities three experimental setups were developed. First, free-fall experiments with spherical particles colliding on a glass pane covered with a water layer were performed at different impact velocities from 0.3 to 1.5 m∙s−1 and water layer thicknesses. Secondly, a pneumatic setup was developed for investigating the maximum liquid bridge length at constant liquid bridge volume and contact velocities from 0.3 to 4.0 m∙s−1. A third setup was used to investigate the liquid bridge behavior during low velocities from 0.0001 to 0.04 m∙s−1. Based on the experimental results, a new model is presented to account for the significant influence of impact velocity on the maximum liquid bridge length.Publicationtype: Journal Article23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Novel approach for measurement of restitution coefficient by magnetic particle tracking(Elsevier, 2022-01); ; ; ; Inter particular contacts between particles are of great interest, as the intensity and quantity of contacts impact the behavior of a wide variety of industrial processes. The coefficient of restitution is commonly used to describe the collision of a particle either with other particles or with walls and components of plant equipment. The coefficient considers the amount of energy that is dissipated in the collision event. Usually the restitution coefficient is examined by the use of high speed cameras and image velocimetry. In this study a new method based on magnetic particle tracking (MPT) was developed to measure the restitution coefficient of magnetic particles. By performing simultaneous image velocimetry and MPT measurements, the novel approach is validated. The comparison shows a high coincidence of the results from both measurement methods, both for normal direction impacts as well as impacts on oblique surfaces. Furthermore, the rotation of particles was investigated (by rolling down a tilted plate), which has also shown the applicability of the MPT measurement method.Publicationtype: Journal ArticleScopus© Citations 11 129 306 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , CFD-DEM simulation of a coating process in a fluidized bed rotor granulator(Multidisciplinary Digital Publishing Institute (MDPI), 2020-09-02); ; ; ; Coating of particles is a widely used technique in order to obtain the desired surface modification of the final product, e.g., specific color or taste. Especially in the pharmaceutical industry, rotor granulators are used to produce round, coated pellets. In this work, the coating process in a rotor granulator is investigated numerically using computational fluid dynamics (CFD) coupled with the discrete element method (DEM). The droplets are generated as a second particulate phase in DEM. A liquid bridge model is implemented in the DEM model to take the capillary and viscous forces during the wet contact of the particles into account. A coating model is developed, where the drying of the liquid layer on the particles, as well as the particle growth, is considered. The simulation results of the dry process compared to the simulations with liquid injection show an important influence of the liquid on the particle dynamics. The formation of liquid bridges and the viscous forces in the liquid layer lead to an increase of the average particle velocity and contact time. Changing the injection rate of water has an influence on the contact duration but no significant effect on the particle dynamics. In contrast, the aqueous binder solution has an important influence on the particle movement.Publicationtype: Journal ArticleScopus© Citations 22 188 175 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Contact behavior of microcrystalline cellulose pellets depending on their water content(Wiley-VCH, 2020-03-12); ; ; ; Microcrystalline cellulose pellets for oral drug delivery are often produced by a combined wet extrusion-spheronization process. During the entire process, the cylindrical as well as the spherical pellets are exposed to various stresses resulting in a change of their shape and size due to plastic deformation and breakage. In this work, the effect of moisture content of pellets on their mechanical behavior is studied. In static compression tests, the strong influence of water content on deformation behavior of pellets is confirmed. Moreover, impact tests are performed using a setup consisting of three high-speed cameras to record pellet-wall collisions. Material properties, such as stiffness, restitution coefficient, breakage force, and displacement, were analyzed depending on the water content.Publicationtype: Journal ArticleScopus© Citations 10 175 324 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental Study and DEM Modelling of the Contact Behaviour of Cylindrical Particles(Curran Associates, Inc., 2019-05); ; ; Publicationtype: Conference Paper6 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dependencies between internal structure and mechanical properties of spray dried granules – Experimental study and DEM simulation(2017-01-01); ; ; The mechanical properties of spray dried granules are decisive with regard to further applications and can be modified via internal granule structure. To obtain the correlations between structural and mechanical properties, necessary experiments are often time and resource consuming. The simulation of varied granule structures and their effect on resulting mechanical properties seems to be a promising approach. In this paper, a model of the particulate internal structure of a spray dried granule was generated with the Discrete Element Method (DEM) based on real structure parameters. The model considers real primary particle number, particle size distribution and radial granule inhomogeneity, what results in the implementation of granule shell thickness and macro void. The internal structure of simulated granules showed significant influence on their mechanical properties. An increase of granule shell thickness and packing density of the primary particles within the shell results in fracture strength increase accompanied by decreasing fracture strain. The simulated reduction of the solid bridge bond size between the primary particles representing the decreasing binder amount leads to decreasing fracture strength and strain as previously determined experimentally (Eckhard et al., 2014). Consequently, the DEM is appropriate for evaluating the effect of changed real internal structure parameters on resulting mechanical granule properties.Publicationtype: Journal Article135