The discrete modelling and understanding of the particle dynamics in fluidized bed apparatuses, mixers, mills and others are based on the knowledge about the physical properties of particles and their mechanical behaviour during slow, fast and repeated stressing. In this paper model parameters (modulus of elasticity, stiffness, yield pressure, restitution coefficient and strength) of spherical granules ( γ -Al 2 O 3 , zeolites 4A and 13X, sodium benzoate) with different mechanical behaviour have been measured by single particle compression and impact tests. Starting with the elastic compression behaviour of granules as described by Hertz theory, a new contact model was developed to describe the force-displacement behaviour of elastic-plastic granules. The aim of this work is to understand the energy absorption during compression (slow stressing velocity of 0.02 mm/s) and impact (the impact velocity of 0.5-4.5 m/s) of granules. For all examined granules the estimated energy absorption during the impact is found to be far lower than that during compression. Moreover, the measured restitution coefficient is independent of the impact velocity in the examined range and independent of the load intensity by compression (i.e. maximum compressive load). In the case of repeated loading with a constant load amplitude, the granules show cyclic hardening with increasing restitution coefficient up to a certain saturation in the plastic deformation. A model was proposed to describe the increase of the contact stiffness with the number of cycles. When the load amplitude is subsequently increased, further plastic deformation takes place and the restitution coefficient strongly decreases.

No abstract

In this paper we experimentally study the effect of collision properties of different particle systems on the bed dynamics of a spout fluidized bed. This is done in different flow regimes: the spout-fluidization regime (case A), the jet-in-fluidized-bed regime (case B) and the spouting-with-aeration regime (case C). The considered particle systems comprise glass beads, γ-alumina oxide and zeolite 4A particles, which are all classified as Geldart D. A non-intrusive measurement technique is used, viz. particle image velocimetry (PIV) to measure the particle flow field in a pseudo two-dimensional (2D) spout fluidized bed. Additionally, digital images are analyzed using a newly developed digital image analysis (DIA) algorithm to evaluate the particle volume fraction. It is demonstrated that the new proposed DIA algorithm provides reliable information on the particle volume fraction, showing that it is a powerful tool when combined with PIV. The added value of DIA is confirmed by comparing the particle velocity fields and volumetric particle fluxes. The particle fluxes display only small differences between the particle systems for each of the examined flow regimes, with the largest difference in the jet-in-fluidized bed regime. In this regime, the flow behaviour of the zeolite 4A particles does not show any features of the spout fluidized bed anymore, but behaviour of an ordinary fluidized bed. This is due to the direct bubble formation above the bottom plate, which results in a large disturbance near the spout entrance. It seems that zeolite 4A particles -because of their small restitution coefficient-tend to cluster in a more pronounced way, producing more bubbles compared to glass beads and γ-alumina oxide particles.

In 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/spoutfluidization 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.Onétudie dans cet article l'effet de l'interaction entre les particules sur la dynamique de lit, en considérant un coefficient de restitution variable. On a fait varier le coefficient de restitution dans le temps et dans l'espace en fonction de la teneur en humidité dueà l'interaction particules-gouttelettes età l'évaporation. Cetteétude aété réalisée par ordinateur,à l'aide d'un modèle d'éléments discretsétendu (DEM). Les régimes d'écoulement examinés comprennent le régime de fluidisation intermédiaire/jaillissement (B1), le régime de jaillissement avec aération (B2) et le régime de jet en lit fluidisé (B3). Pour tous ces régimes d'écoulement, 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'écoulement 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 l'évaporation sur la distribution du coefficient de restitution s'observe seulement pour le régime de jet en lit fluidisé (B3), où la vitesse de fond est relativementélevée, augmentant ainsi l'évaporation des particules dans la région de l'espace annulaire. Ceci se reflète dans la hauteur de lit moyennée pour le cas testé avecévaporation, qui est plus grande que dans le cas testé sansévaporation. Une h...

und mit einer rheologischen Messmethode durchgeführt und deren Aussagekraft mit einander verglichen.Der Vergleich beider Methoden zeigt, dass die rheologische Messmethode besser für diese Aufgaben geeignet ist, denn sie liefert detaillierte und signifikante Aussagen über die Materialeigenschaften.