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Item type:Publication, Access status: without files , Comparison of fibre optical measurements and discrete element simulations for the study of granulation in a spout fluidized bed(2006-04); ; ; ; Spout fluidized beds are frequently used for the production of granules or particles through granulation. The products find application in a large variety of applications, for example detergents, fertilizers, Pharmaceuticals and food. Spout fluidized beds have a number of advantageous properties, such as a high mobility of the particles, which prevents undesired agglomeration and yields excellent heat transfer properties. The particle growth mechanism in a spout fluidized bed as function of particle-droplet interaction has a profound influence on the particle morphology and thus on the product quality. Nevertheless, little is known about the details of the granulation process. This is mainly due to the fact that the granulation process is not visually accessible. In this work we use fundamental, deterministic models to enable the detailed investigation of granulation behaviour in a spout fluidized bed. A discrete element model is used describing the dynamics of the continuous gas-phase and the discrete droplets and particles. For each element momentum balances are solved. The momentum transfer among each of the three phases is described in detail at the level of individual elements. The results from the discrete element model simulations are compared with local measurements of particle volume fractions as well as particle velocities by using a novel fibre optical probe in a fluidized bed of 400 mm I.D. Simulations and experiments were carried out for two different cases using Geldart B type aluminium oxide particles: a freely bubbling fluidized bed and a spout fluidized bed with the presence of droplets. It is demonstrated how the discrete element model can be used to obtain information about the interaction of the discrete phases, i.e. the growth zone in a spout fluidized bed. Eventually this kind of information can be used to obtain closure information required in more coarse grained models.Publicationtype: Conference Paper17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical solutions of a two-dimensional population balance equation for aggregationA new discretization for a two dimensional aggregation population balance equation is developed. The discretization is an extension of the cell average technique proposed by the authors (J. Kumar et al. 2006, Chem. Eng. Sci. 61, 3327-3342) for one dimensional aggregation problems. The scheme is based on an exact prediction of certain moments of the population. The formulation is quite simple to implement, computationally less expensive than previous approaches and highly accurate. Numerical diffusion is a common problem with many numerical methods while applied on coarse grids. The presented technique nearly eliminates numerical diffusion and predicts three moments of the population at high accuracy. This is achieved by taking the average of all newborn particles in a cell and then assigning them to neighboring cells according to the cell average and the distance to neighboring nodes. The technique may be implemented on any type of grid. The accuracy of the scheme has been analyzed by comparing analytical and numerical solutions of a test problem. The numerical results are in excellent agreement with the analytical results and show the ability to predict higher moments very precisely. Additionally, an extension of the proposed technique to higher dimensional problems has been discussed.Publicationtype: Conference Paper35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical bifurcation analysis of the nonlinear dynamics in continuous fluidized bed spray granulation systems(2006-04); ; ; ; Nonlinear oscillations in continuous fluidized bed spray granulation with external product classification are analyzed. Using methods from numerical bifurcation analysis the size and location of the instability regions in the space of the design parameters and the adjustable operating parameters are predicted and discussed. Analysis is based on a new relatively simple population balance model, which is formulated on a mass basis and provides first qualitative insights into the nonlinear dynamic behavior of continuous fluidized bed spray granulation processes.Publicationtype: Conference Paper10