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Dynamiques d'écoulements gaz/particules en conduite verticale

Abstract : The dynamics of dry granular flows in a vertical pipe has been studied both experimentally and theoretically.
At high and medium grain flow rates, one observes respectively a free fall regime and a density waves regime (sequences where dense regions and dilute zones alternate). A model has been developed to predict the relations between different parameters (flow rate, pressure, particle fraction); it demonstrates, in particular, the key part played by the interactions between air and the grains. This allows one to estimate friction forces between the grains and the walls and the various components of air and grain transport in the tube.
At low grain flow rates, an intermittent compact flow where pressure and particle fraction are strongly correlated is observed. A clear amplification of the pressure and particle fraction variations as the decompaction wave propagates upwards at the onset of the flow has been observed. These results can be reproduced by numerical simulations demonstrating the key role of the interactions between air and the grains. We have realized a specific study of the variation of the screening of the grains weight in a packing inside a vertical tube in relative motion. This study demonstrates that Janssen's model remains valid over a broad range of velocities. In addition, the motion of the walls induces a readjustment of the force distribution in the packing, reaching a very reproducible state. The dependence of these results on the relative humidity has been investigated and a strong influence on the grains/walls interactions has been demonstrated.
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Contributor : Yann Bertho <>
Submitted on : Wednesday, September 12, 2007 - 9:46:48 PM
Last modification on : Wednesday, September 16, 2020 - 4:32:22 PM
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Yann Bertho. Dynamiques d'écoulements gaz/particules en conduite verticale. Analyse de données, Statistiques et Probabilités [physics.data-an]. Ecole Polytechnique X, 2003. Français. ⟨tel-00171722⟩

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