1,721,093 research outputs found
CFD SIMULATIONS OF THE MIXING OF INERT POLYDISPERSE FLUIDIZED SUSPENSIONS USING QMOM & DQMOM
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Direct Quadrature Method of Moments for the Mixing of Inert Polydisperse Fluidized Powders and the Role of Numerical Diffusion
No full textInvestigation into the dynamics of polydisperse fluidized beds by using the direct quadrature method of moments
No full textNew quadrature-based moment method for the mixing of inert polydisperse fluidized powders in commercial CFD codes
Full text linkTo describe the behavior of polydisperse multiphase systems in an Eulerian framework, we solved the population balance equation (PBE), letting it account only for particle size dependencies. To integrate the PBE within a commercial computational fluid dynamics code, we formulated and implemented a novel version of the quadrature method of moments (QMOM). This no longer assumes that the particles move with the same velocity, allowing the latter to be size-dependent. To verify and test the model, we simulated the mixing of inert polydisperse fluidized suspensions initially segregated, validating the results experimentally. Because the accuracy of QMOM increases with the number of moments tracked, we ran three classes of simulations, preserving the first four, six, and eight integer moments of the particle density function. We found that in some cases the numerics corrupts the higher-order moments and a corrective algorithm, designed to restore the validity of the moment set, has to be implemented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
X-ray imaging of horizontal jets in gas fluidised bed nozzles
Full text linkThe design of the fluidising air distributors, or nozzles, is one of the most important aspects influencing operation of fluidised beds at industrial scale. In this work, the study of the hydrodynamics in gas-solid fluidized beds where the primary gas injection is achieved through a nozzle-type gas distributor has been carried out, using an innovative X-ray imaging technique. Qualitative and quantitative results are reported, with particular focus on jets penetration length and their evolution. Results show that the lighter and the finer are the particles, the larger is the jet penetration. Since the experimental data do not match predictions available in literature, a new non-dimensional correlation based on hydrodynamic scaling and Froude number is also proposed. The new correlation takes into account the effects of jet velocity, particle density and particle size. A tentative mechanistic explanation for the departure from purely hydrodynamic scaling is offered
Bulk flow properties of sieved samples of a ceramic powder at ambient and high temperature
No full textThe flow properties of five samples of a ceramic powder, characterized by different particle size distributions were measured at ambient temperature and at 500. °C with the High Temperature Annular Shear Cell. A significant increase of powder cohesion was observed at high temperature. A model combining a continuum approach and a particle-particle interaction description was used to correlate the powder tensile strength with the interparticle forces. The dependence of the tensile strength on powder consolidation and temperature is correctly described by the model
Detection and estimation of capillary interparticle forces in the material of a fluidized bed reactor at high temperature by powder flow characterization
Full text linkTwo ceramic powder samples having different compositions of surface impurities and particle size distributions were considered. These two samples resulted from a high temperature fluidized bed reactor which in its operation showed changes of working condition that might be attributed to the onset of strong interparticle forces. The flow behaviour of these powders was characterized by the High Temperature Annular Shear Cell (HT-ASC), between ambient temperature and 500 °C. Furthermore, a model is developed to relate the change of the powder flowability to the formation of a liquid phase due to the melting of particle impurities present on the particle surface. In particular, the model is used to predict, on the base of the salt composition, the intensity of the interparticle forces at different temperatures. The interparticle forces predicted by the model can be compared with those that can be inferred from the powder flow properties measured with the HT-ASC. Therefore, it is demonstrated that it is possible to derive a theoretical model to predict interparticle forces in a particulate material relevant to fluidized bed reactor, on the basis of the impurities composition. Furthermore, it is demonstrated the possibility to correctly estimate the intensity of average interparticle forces in the same kind of material by the interpretations of bulk flow properties measured with a shear tester, even in the case in which capillary forces take the place of the much weaker van der Walls forces. More in general, the paper suggests a method by which powder rheology can be used to indirectly evaluate the effects of the interparticle forces on fluidization processes even in case in which strong capillary interaction occur
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