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Caractérisation par trajectographie tridimensionnelle du mélange dans un réacteur agité

Abstract : This work deals with the utility of a lagrangian approach for flows and mixing characterisation. This novel approach fills the gap between complete eulerian descriptions and global systemic methods. Using two CCD cameras, it consists in tracking over a long period (twenty minutes to one hour) the displacements of a small particle (diameter: 2 mm) that is supposed to be a perfect passive tracer of the fluid. After image analysis, the threedimensional trajectory can be reconstructed. The trajectory represents a compact but high amount of information. Thus, this information is analysed thanks to a series of tools, which are more or less linked with usual mixing parameters : velocity properties, fluid homogenization, spatial and temporal trajectories structures. This characterisation is applied to turbulent flows (three different impellers, effect of rotation speed and their vertical position), viscous newtonian fluids (influence of both viscosity and rotation speed, as proposed by the Reynolds number definition) and non-newtonian fluids (existence of cavities and modification of flows structure with operating conditions). Those applications underscore the capacities of the trajectography method to characterise mixing processes and to classify several agitation configurations. At last, through an investigation on the flow in an open reactor, the Residence Time Distribution (RTD) obtained with the particle is compared to the usual molecular RTD. Moreover, this last application of trajectography contributes to the illustration of the Trajectory Length Distribution (TLD) concept and leads to a comparison between RTD and TLD.
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Pascal Pitiot. Caractérisation par trajectographie tridimensionnelle du mélange dans un réacteur agité. Alimentation et Nutrition. Institut National Polytechnique de Lorraine, 1999. Français. ⟨NNT : 1999INPL080N⟩. ⟨tel-01750632⟩



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