Air/grains interactions in confined medium


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.
Publications

Variations de pression dans un écoulement granulaire dense intermittent 

Y. Bertho, Bull. Soc. Fr. Phys. 149, 46 (2005) 

Écoulements incontrôlés 

Y. Bertho, Pour la Science 311, 1819 (2003) 

Dynamiques d'écoulements gaz/particules en conduite verticale 
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Y. Bertho, Thèse de l'École Polytechnique (2003) 

Intermittent dry granular flow in a vertical pipe 
[  ] 
Y. Bertho, F. Giorgiutti and J.P. Hulin, Phys. Fluids 15, 33583369 (2003) 

Powder flow down a vertical pipe: the effect of air flow 
[  ] 
Y. Bertho et al., J. Fluid Mech. 459, 317345 (2002) 
