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Item type:Publication, Access status: without files , Dynamic model development based on experimental investigations of acoustically levitated suspension dropletsThe investigation and modeling of the evaporation rates and particle formation for spray drying processes is usually performed on the scale of single droplet drying experiments. Especially the solidification processes of suspension drops and the resulting evaporation rates in the second drying stages are not yet fully understood. In an extensive parameter study, the drying mechanisms in an insulated acoustic levitator are evaluated at varying gas temperatures, relative humidities and drop compositions. Based on design of experiments, a methodical approach for the empirical model development of the drying rates in the first and second drying stages is presented. It is shown, that the drop deformation has to be considered when modeling the evaporation. A qualitative analysis of the resulting particle morphologies is given and a dynamic model for the complete single droplet drying experiment is presented.Publicationtype: Journal Article139 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Measurement of residence time distributions in a continuously operated spouted bedContinuous gas-solid processes are applied in many industries with particulate products, e.g. for granulation or coating. In this contribution, the residence time behavior in a continuously operated prismatic spouted bed was determined by applying an impulse of magnetizable tracer particles. Experiments were performed with the original configuration and with separation plates including mouse holes of varying size between the different chambers of the ProCell 25 apparatus. It is shown that the shape of the residence time distribution is influenced by the separation plates. In order to quantify the backmixing between the chambers, discontinuous experiments were performed, and the bed mass distribution and the distribution of the tracer were measured and compared to the initial conditions.Publicationtype: Journal ArticleScopus© Citations 8 242 347 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of binary and ternary particle systems on the spouting stability in a three-dimensional prismatic spouted bed(2019-12-01); ; ; ; In this contribution, a three-dimensional prismatic spouted bed for coating and granulation purposes is investigated. To determine the influence of a particle size distribution on the spouting behavior, binary and ternary mixtures of different particle sizes (γ-Al2O3 particles) are used. The stability is quantified using the Fourier transforms of the pressure drop signals. The stability range of binary and ternary systems differs from the monodisperse systems. Both the lower and the upper velocity limits of stable spouting can be described by a power function dependent on the Reynolds number and the Archimedes number. A larger Archimedes number results in an increased Reynolds interval size of stable spouting, which refers to a larger size of the velocity interval. This correlation was found to be not valid for the mass equivalent mixture of three particle fractions where no stable spouting state was obtained. In addition, clustering and segregation effects were observed: Coarse particles accumulate in the spout and fine particles in the annulus region of the regarded prismatic spouted bed in case of the instable spouting regime. This is problematic for granulation and coating processes as a homogeneous droplet distribution and a proper mixing between spraying and drying zones is disabled if some particle fractions are inhibited to pass the spray zone.Publicationtype: Journal Article149 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Measurement of Residence Time Behavior in a Continuously Operated Spouted BedPublicationtype: Conference Paper43 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A novel method of quantifying the coating progress in a three-dimensional prismatic spouted bedPublicationtype: Journal Article94 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Novel production method of tracer particles for residence time measurements in gas-solid processesIn order to measure the residence time distribution (RTD) in continuous gas-solid processes tracer particles are used. In this contribution, a novel production concept for magnetizable particles has been developed and optimized. The process includes coating of a fraction of the investigated bed material with a magnetizable paint in a laboratory spouted bed. The coated particles fulfill the requirements of tracer material, are resistant, harmless to health and reusable. After passing a continuously operated process, the tracer material can be separated by a magnetic rod from the sample, which allows the fast and easy calculation of the exit age distribution as demonstrated in this contribution with a horizontal fluidized bed.Publicationtype: Journal Article205 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental and numerical investigation of a three-dimensional prismatic spouted bed with liquid injection(2018-04-22); ; ; ; In this contribution, a three-dimensional prismatic spouted bed for coating purposes is investigated experimentally and numerically. Spouting behavior was experimentally investigated by means of Fourier transform of the pressure drop signal. The spouting stability could be increased by two parallel draft plates and influenced by using binary or ternary mixtures of different particle sizes. Simulations were performed with a coupled CFD-DEM approach, whereby droplets were injected in a post-processing step, which allowed the estimation of the liquid surface coverage of the used Y-AI2O3 particles. It was found that the insertion of draft plates results in a broader liquid distribution in the first ten seconds of the process. By applying the recurrence CFD (rCFD) method, the broader liquid distribution could be confirmed for a process duration of 1 hour.Publicationtype: Conference Paper175 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of gas inflow modelling on CFD-DEM simulations of three-dimensional prismatic spouted beds(2018-04-15); ; ; ; In this contribution, coupled CFD-DEM simulations of a three-dimensional prismatic spouted bed with two tangential, parallel gas inlets are presented. Contact model parameters were calibrated. Simulations with different inlet conditions were performed, whereby an additional degree of freedom by merging the two inlets was found to match the experimentally observed bed behavior. Additionally, it was shown that the inlet slit pressure drop has an important influence on spouting stability. By adjusting the inlet conditions, calibrating the particle interaction model parameters and applying fluid-coarsening correction of the Beetstra drag model, an experimentally validated model was obtained.Publicationtype: Journal Article220 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , CFD-DEM modelling of circulation frequencies and residence times in a prismatic spouted bed© 2018 Institution of Chemical Engineers Coupled CFD-DEM simulations of a three-dimensional prismatic spouted bed with liquid injection were performed. Spouting stability is investigated by means of pressure drop fluctuation analysis and high speed camera recording. To determine the influence of flow stability on coating quality, droplets are injected in a post-processing step and deposited on colliding solid parcels. In order to estimate liquid holdup in the bed, heat transfer and subsequent evaporation of the surface liquid film were modelled. The coating quality of different process conditions is compared for a simulation time of 10 s and found to be broader distributed in the dense stable spouting operating regime. The analysis of particle circulation frequencies shows slower circulation under stable spouting conditions, resulting in a slower coating progress. This explains the inhomogeneous coating quality in the first 10 s for these cases. Nevertheless, the frequencies are less broadly distributed compared to the instable regime, which is advantageous for obtaining a homogeneous layer in real-time coating processes.Publicationtype: Journal Article237 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , CFD-DEM modeling of a three-dimensional prismatic spouted bedIn this contribution coupled CFD-DEM-simulations of a laboratory prismatic spouted bed with two horizontal gas inlets are presented. With regard to a feasible simulation time, the simulations are parallelized and a coarse-graining approach is used in order to handle a high amount of particles. Different drag models are used within the simulations to evaluate their applicability to represent the experimental results. The spouting stability is analyzed by means of the time-dependent pressure drop behavior. The influence of draft plates in the process chamber on the particle flow patterns and spouting stability is investigated both numerically and experimentally. By means of simulations, the residence times of particles within the spray zone are evaluated for different gas flow rates.Publicationtype: Journal Article127