The present paper is dedicated to numerical and experimental study of the hydrodynamic of a non-reactive isothermal pressurized fluidized bed. Experimental data have been obtained using PEPT technique allowing to track a particle trajectory inside a dense fluidized bed. A specific post-processing approach has been developed to compute the Eulerian time-averaged particle velocity field. The comparison with 3-dimensional numerical model predictions shows a good agreement in the core of the fluidized bed. In contrast, in the near wall region the numerical model overestimate the downward particle velocity. The modification of particle phase wall boundary condition improves the numerical predictions.
Re´sume´-É tude multi-e´chelle d'un lit fluidise´dense re´actif de type re´ge´ne´rateur FCC -Ce travail porte sur les e´coulements re´actifs gaz-particules tels que ceux que l'on rencontre dans la combustion du coke pour la re´ge´ne´ration des particules de catalyseurs de FCC. Les e´tudes re´alise´es pour de tels e´coulements montrent qu'en ge´ne´ral le taux de re´action global au cours du temps est mal pre´dit. La raison peut eˆtre lie´e a`la cine´tique chimique utilise´e qui est en ge´ne´ral base´e sur des expe´riences macroscopiques. Le lien entre des releve´s macroscopiques et une cine´tique chimique de re´action he´te´roge`ne locale qui a lieu a`l'interface meˆme entre la surface de la particule et le gaz environnant n'est pas imme´diat. Nous avons utilise´des re´sultats cine´tiques issus d'expe´riences afin d'identifier les proble`mes qui apparaissent lorsque l'on utilise cette meˆme cine´tique pour des e´chelles diffe´rentes. Une analyse multi-e´chelle est donc effectue´e. Nous montrons alors que la fraction volumique de particules a une influence sur le taux de re´action. Par ailleurs, nous montrons la ne´cessite´de de´velopper un mode`le de sous-maille pour le taux de re´action lie´a`la pre´sence de clustering dans les e´coulements gazparticules. Dans les calculs effectue´s couramment, le taux de re´action est calcule´en conside´rant une re´partition homoge`ne des particules a`l'inte´rieur de la maille de calcul. En effet l'analyse microscopique montre que lorsque les particules sont regroupe´es en nuages denses, la fraction massique de dioxyge`ne a`l'inte´rieur de ce nuage est rapidement nulle et donc le dioxyge`ne est en de´faut. La re´action he´te´roge`ne est donc limite´e.Abstract -Multiscale Study of Reactive Dense Fluidized Bed for FCC Regenerator -This study deals with reactive gas particle flows like the coke combustion during the regeneration of FCC particles. In this kind of reactive flow, the global reaction rate is usually bad predicted. In a first approximation, the chemical scheme can be the reason because of the limitation of its modeling. It is usually based on macroscopic experimental results. The link between these macroscopic measurements and a local kinetics of the heterogeneous reaction occuring at the gas-particle interface is not confirmed. Results of kinetics coming from experimental measurements are used and we try to highlight the problems that appear when the same kinetics are used at different scales. In common industrial computations, coarse meshes are used to solve continuity equations. Averaged or filtered Navier-Stokes and species continuity equations have to be solved in which additional correlation terms appear because of non-linear terms in the original equations, including reaction rate correlation. Therefore a multiscale analysis is performed in order to improve the modeling of this terms. This paper, shows that the eulerian formulation of kinetics has to be improved due to the impact Oil & Gas Science and Technology -Rev. IFP Energies nouvelles, Vol. 68 (2013), No. ...
<div class="section abstract"><div class="htmlview paragraph">This paper introduces the Lagrangian particle tracking technology readily available in Ansys Fluent in the in-flight icing simulation workflow, which normally uses the Eulerian approach for droplet flows. The Lagrangian solver is incorporated in the Fluent Icing workspace which is to become the next-gen in-flight icing simulation tool provided by Ansys. Lagrangian tracking will eventually be used for SLD and ice crystal rebound and re-impingement calculations in the Ansys workflow. Here we introduce some preliminary results with the current state of its implementation as of Fluent Icing release 2023R2. Example cases include several selections from the 1<sup>st</sup> Ice prediction workshop with experimental comparisons as well as results obtained earlier with the Eulerian droplet solution strategy. Collection efficiency comparisons on clean geometries show good agreement between Eulerian and Lagrangian methods when the particle seeds are in the millions range. Shadow zones are resolved with more clarity when Lagrangian tracking is used. SLD and ice crystal rebound simulations significantly benefit from the Lagrangian method, as all wall interaction instances per track can be resolved in a single pass. Turbulent dispersion effects that are built-in to Fluent’s Lagrangian tracking are studied. The impact of turbulent boundary layers on small droplets is investigated. A change in collection efficiency due to particle velocities redistribution when they go across a turbulent structure is observed on a simple test case but the impact of turbulent dispersion on the validation cases collection efficiency is negligible. Multi-shot icing simulations on swept wings produce more detailed ice shapes for the same number of shots when Lagrangian method is swapped in for the Eulerian solver.</div></div>
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