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A comprehensive physical model describing the agglomeration behavior present during fluidization of fine powders is still missing in literature. A model of balance of forces acting on a single solid particle is introduced, aiming at predicting and locally estimating the size of the agglomerates created in the bed. Computational fluid dynamics (CFD) have been used to investigate the hydrodynamics of a gas-solid fluidized bed operated with particles belonging to group A of Geldart classification.1 The key issue is that, in the gas and particle flow field, both hydrodynamic and interparticle forces are of importance. The model is incorporated into simulations based on an Eulerian approach and using the kinetic theory of granular flow. In the simulations, the closure models describing the hydrodynamics of the solids phase are directly affected by the behavior of the agglomerates. No empirical data or parameters were used to close the model. The simulations are compared with experiments of an independent research group, through the time-averaged solids volume fraction in a fluidized bed operated at different gas velocities. The agreement obtained between the simulation results and data from the literature is very good. Also, it is shown that, under flow conditions treated in this work, agglomerates of size of several single particle diameters are present in the fluidized bed.

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In the current work a detailed study is performed of the turbulent-to-laminar transition at the inlet of an automotive monolithic reactor. The effects of the transition on the conversion of gaseous species and on the deposition of particulate matter are investigated using numerical simulations. Two main effects of the turbulence on the conversion in the monolith have been identified: slow fluctuations due to turbulent eddies that are too large to enter the channels and rapid fluctuations due to smaller turbulent eddies that penetrate the channels. It is also shown that inertial particles may deposit inside the monolith channels, providing a likely explanation of the experimentally observed spatial deposition profiles of elements that chemically deactivate automotive catalysts.

Crystallization has been observed in laser-induced cavities in saturated solutions, but the mechanisms behind nucleation of crystals are not entirely clear. A hypothesis is that high solution supersaturation during the bubble growth period triggers the nucleation. Because of small spatiotemporal scales of the cavitation event, the supersaturation is very difficult to measure experimentally. To test the nucleation hypothesis, we perform a two-dimensional axisymmetric direct numerical simulation of an experimentally observed laser-induced cavitation event with crystallization. We demonstrate a significant degree of supersaturation and argue that the nucleation hypothesis is indeed plausible. To analyze factors that lead to a high supersaturation, we develop a comprehensive one-dimensional model for spherical laser-induced cavities. We conduct an extensive investigation on how the solute solubility, solute diffusivity, laser pulse energy, and superheated liquid volume affect the supersaturation. We show that high supersaturation is possible under a range of relevant conditions but not readily obtained for all solutions and laser setups. Guidelines are provided to identify if a specific solution or laser setup may attain high supersaturation. The insights obtained and the numerical methods formulated in this work can be applied to assess and design new laser-induced cavitation setups that allow for precise control of the duration and degree of the supersaturation.

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