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Item type:Publication, Access status: without files , Magnetic monitoring of a single particle in a prismatic spouted bed(2009-09-23); ; ; In this work a non-intrusive measuring technique for continuous tracking of a magnetic marked particle during fluidization in a prismatic spouted bed is presented. The magnetic monitoring system provides besides the spatial coordinates x, y and z the orientation of the particle, whereby the trajectory, the velocity, the acceleration as well as the rotation of the particle are obtained. It will be demonstrated that the characteristic particle trajectories and particle velocity distributions in dependency of the gas throughput and of the bed mass can be detected in this type of spouted bed. Furthermore, a calculated particle velocity distribution obtained by a CFD continuum simulation will be favorably compared with a measured distribution.Publicationtype: Journal Article17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of liquid layers on energy absorption during particle impact(2009-08); ; ; The influence of the thickness of a covering liquid layer and its viscosity as well as the impact velocity on energy loss during the normal impact on a flat steel wall of spherical granules with a liquid layer was studied. Free-fall experiments were performed to obtain the restitution coefficient of elastic-plastic γ-Al2O3 granules by impact on the liquid layer, using aqueous solutions of hydroxypropyl methylcellulose with different concentrations for variation of viscosity (1-300 mPa s). In the presence of a liquid layer, increase of liquid viscosity decreases the restitution coefficient and the minimum thickness of the liquid layer at which the granule sticks to the wall. The measured restitution coefficients were compared with experiments performed without liquid layer. In contrast to the dry restitution coefficient, due to viscous losses at lower impact velocity, higher energy dissipation was obtained. A rational explanation for the effects obtained was given by results of numerically solved force and energy balances for a granule impact on a liquid layer on the wall. The model takes into account forces acting on the granule including viscous, surface tension, capillary, contact, drag, buoyancy and gravitational forces. Good agreement between simulations and experiments has been achieved.Publicationtype: Journal Article12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Characterization and CFD-modeling of the hydrodynamics of a prismatic spouted bed apparatus(2009-07-15); ; ; ; Recently the importance of spouted bed technology has significantly increased in the context of drying processes as well as granulation, agglomeration or coating processes. However, the understanding of the complex interactions within and between the single phases is still low and needs further improvement. Several research groups apply both continuum as well as discrete element simulations to understand the hydrodynamics of the spouting process. This work focuses on the simulation of the hydrodynamic behavior of a prismatic spouted bed apparatus by applying the Euler/Euler continuum approach in the commercial computational fluid dynamics (CFD) software package FLUENT 6.2. The simulations are validated by experiments. Calculated and experimental (by PIV-measurements) obtained velocity vector maps, as well as measured and calculated gas phase pressure fluctuations over the entire bed are compared. The aim of this work is to improve the understanding of the hydrodynamics of the spouting process.Publicationtype: Journal Article29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Energetic aspects of granule impact: Influence of the liquid layers(2009-07); ; The influence of the thickness (40 um - 1 mm) and the viscosity (1-300 mPa-s) of the liquid layer at the contact as well as impact velocity (1-2.4 m/s) on the energy dissipation during the normal impact of spherical granules was investigated. Using a free-fall device the restitution coefficients of γ-Al2O3 granules impacted on a steel wall with a liquid layer were measured. With increasing liquid viscosity the restitution coefficient and the critical thickness of liquid layer at which the granule sticks decreased. With decreasing impact velocity the restitution coefficient greatly decreases. A rational explanation of obtained effects was given by results of numerically solved force and energy balances.Publicationtype: Conference Paper19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Three-dimensional computational fluid dynamics modeling of a prismatic spouted bed(2009-05-20); ; ; ; Modern simulation tools like discrete particle models or continuum models have been established as precious methods to gain insight into the complex processes in fluidized and spouted beds. Valuable information on parameters influencing the hydrodynamics can be obtained directly from computer simulations. Numerous researchers applied two-dimensional discrete and continuum models to simulate fluidized and spouted beds. However, only few publications deal with three-dimensional continuum simulations, and very often results of three-dimensional experiments are compared with two-dimensional results. In this work, a three-dimensional simulation by application of a continuum model is presented in a prismatic spouted bed with slit-shaped gas inlets. Comparisons with two-dimensional simulations in the same geometry (Gryczka et al. 2009, Chem. Eng. Sci., in press) are also part of this publication. The influence of the third dimension on the hydrodynamic behavior (bubble formation, bubble size, etc.) will be discussed. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.Publicationtype: Journal Article21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , New developments in fluidization technology(2009-05-20); Werther, JoachimPublicationtype: Editorial10 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Discrete particle simulation study on the influence of the restitution coefficient on spout fluidized-bed dynamics(2009-05-20); ; ; ; Spout fluidized beds find widespread application in the process industry in granulation processes, in which efficient contacting between large particles, droplets and gas is of paramount importance. However, detailed understanding of the complex behavior of these systems is lacking. In this paper, we study the effect of the inter-particle interaction on the bed dynamics, by investigating the bed dynamics as a function of the restitution coefficient. This is done computationally, with the use of an extended discrete particle model. The examined flow regimes comprise the intermediate/spout-fluidization regime (B1), the spouting-with-aeration regime (B2) and the jet-in-fluidized-bed regime (B3). The pressure drop and the vertical particle velocity are compared to experimental data obtained by Link (Chem. Eng. Sci. 2007, 62, 195). The computed results with en = 0.97 show the same resemblance with the experiments. It is shown that, if the restitution coefficient decreases, more bubbles are present causing more pronounced heterogeneity (instability) in the overall flow structure of the bed, to more or less extent dependent on the flow regime. The particle velocity and root mean square profiles confirm the effect on the stability of the bed and show that the spout channel for cases B1 and B3 becomes unstable when the restitution coefficient decreases. For case B2, a transition occurs from the spouting-with-aeration to the intermediate/spout-fluidization regime at low restitution coefficient. These findings show the great importance of the influence of the restitution coefficient on the dynamics of the bed. During the granulation process, when the particles contain different moisture contents, regions in the bed exist that contain particles with different restitution coefficients. These regions thus experience different dynamics, resulting in varying performance. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.Publicationtype: Journal Article23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Wood gasification in a lab-scale bubbling fluidized bed: Experiment and simulation(2009-05); ; ; ; In theory, an integrated biomass gasification and fuel cell system has a higher overall plant efficiency when compared to the efficiency of biomass gasification combined with simple combustion systems and gas engines. In order to develop a prototype of this new concept of power plant operating in the range of 150kW to 5MW, several institutes of the Max Planck Society and the Fraunhofer-Gesellschaft in Germany have been working on the ProBio project with focus on the theoretical and experimental investigation of an integrated 1-2kWe system. The paper will firstly describe the gasification unit of the system: a lab-scale atmospheric bubbling fluidized bed gasifier. Wood gasification experiments were conducted and the influence of operation parameters, i.e. gasification agents, equivalence ratio ER and steam to biomass ratio S/B on gas yield and gas composition was analyzed. In parallel with the experimental work, chemical kinetics of wood gasification was studied and simulated. Furthermore, simulation of bubbling fluidized bed hydrodynamics at high temperature, using commercial computational fluid dynamics (CFD) software FLUENT, was also conducted to better understand the phenomenon of fluidization inside the bed.Publicationtype: Conference Paper15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , CFD modeling of a prismatic spouted bed with two adjustable gas inletsSince the invention of the spouted bed technology by Mathur and Gishler (1955), different kinds of apparatus design were developed and a huge number of applications in nearly all branches of industry have emerged. Modeling of spouted beds by means of modern simulation tools, like discrete particle models or continuum models, has become a precious opportunity to understand the complexity of multiphase flows in these apparatus. In this work, two-dimensional continuum simulations of a novel kind of spouted bed apparatus with adjustable gas inlets are presented. Different gas-particle drag models are used to obtain a realistic flow structure. Simulated solid phase concentrations are compared with images taken during experiments. Furthermore, simulated and measured gas phase pressure fluctuations over the entire bed are contrasted allowing more accurate comparisons between the simulated and the real hydrodynamic behaviour of the spouted bed. Depuis I'invention de la technologie du lit jaillissant par Mathur et Gishler (1955), unegrande variété de systèmes a été mise au point et un nombre considérable d'applications dans presque toutes les branches de I'industrie ont vu le jour. La modelisation de I its jaillissants au moyen d'outils de simulation modemes, tels que les modeles de particules disc rets ou les modeles en continu, est une excellente occasion pour comprendre la complexité des écoulements multiphasiques dans ces appareils. Dans ce travail, des simulations en continu bidimensionnelles d'une nouveau type de lit jaillissant avec des entrees de gaz ajustables sont présentées. On a testé différents modèles de trainée gaz-particules pour obtenir une structure d'écoulement réafiste. Les concentrations de phases solides simulées sont comparées a des images prises lors des expériences. Par ailleurs, les fluctuations de pression de phase gazeuse simulées et mesurées dans la totalité du lit sont contrastées, ce qui permet des comparaisons plus precises entre le comportement hydrodynamique simule et reel du lit jaillissant. © 2009 Canadian Society for Chemical Engineering.Publicationtype: Journal Article15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A discrete element study of wet particle-particle interaction during granulation in a spout fluidized bedIn this article we study the effect of the inter-particle interaction on the bed dynamics, by considering a variable restitution coefficient. The restitution coefficient is varied in time and space depending on the moisture content due to the particle-droplet interaction and evaporation. This study is done computationally, by using an extended discrete element model (DEM). The examined flow regimes comprise the intermediate/spout- fluidization regime (B1), spouting-with-aeration regime (B2) and the jet-in-fluidized-bed regime (B3). For all flow regimes, the averaged bed height increases with decreasing restitution coefficient. Moreover, the averaged bed height for a variable restitution coefficient is larger for all flow regimes compared to a case with a constant restitution coefficient, indicating that the distribution of the restitution coefficient influences the bed dynamics. The effect of evaporation on the distribution of the restitution coefficient is only observed for the jet-in-fluidized-bed regime (B3), where the background velocity is relatively high leading to enhanced evaporation from the particles in the annulus region. This is reflected in the averaged bed height for the evaporation test case, which is larger compared to a test case without evaporation. A larger bed height for cases with variable restitution coefficient is due to the pressure build up in the spout region caused by the longer closing period of the spout channel. This is confirmed by the recorded pressure fluctuation signal and its root mean square which are larger for the cases with the variable restitution coefficient. On étudie dans cet article I'effet de I'interaction entre les particules sur la dynamique de lit, en considerant un coefficient de restitution variable. On a fait varier le coefficient de restitution dans le temps et dans I'espace en fonction de la teneur en humidite due à I'interaction particules-gouttelettes et a I'evaporation. Cette étude a été réalisée par ordinateur, à I'aide d'un modèle d'elements discrets étendu (DEM). Les regimes d'écoulernent examinés comprennent le régime de fluidisation intermediaire/jaillissement (BI), le régime de jaittissement avec aeration (B2) et le régime de jet en lit fluidisé (B3). Pour tous ces régimes d'écoulernent, la hauteur de lit moyennée augmente avec la diminution du coefficient de restitution. En outre, la hauteur de lit moyennée pour un coefficient de restitution variable est plus grande pour tous les régimes d'écoulernent comparativement au cas du coefficient de restitution constant, ce qui indique que la distribution du coefficient de restitution influence la dynamique de lit. L'effet de I'évaporation sur la distribution du coefficient de restitution s'observe seulement pour le régime de jet en lit fluidisé (B3), ou la vitesse de fond est relativement élevée, augmentant ainsi I'evaporation des particules dans la région de I'espace annulaire. Ceci se reflete dans la hauteur de lit moyennée pour le cas testé avec évaporation, qui est plus grande que dans le cas testé sans evaporation. Une hauteur de lit plus grande pour les cas avec coefficient de restitution variable est due à la montée de la pression dans la région du jaillissement qui est causée par la période de fermeture plus longue de la conduite de jaillissement. Ceci se continue par le signal de fluctuation de pression enregistré et son écart quadratique moyen qui sont plus grands pour les cas avec coefficient de restitution variable.Publicationtype: Journal Article29