Spécification des charges et des écoulements dans les silos métalliques

Abstract

RésuméCet article présente une partie des travaux effectués dans le cadre de la « Mis sion Silos » en collaboration avec le CTICM.Deux aspects nous ont intéressés : d'abord l'analyse des différents types d'écou lement durant la vidange caractérisés par la détermination des profils de vitesse sur modèle réduit ; ensuite l'interprétation des résultats des mesures expérimen tales des efforts en paroi comparés aux méthodes de calculs de WALTERS, SOKOL et à la norme DIN.Cette analyse comparative démontre que les modèles de calcul établis dans le cas d'un écoulement en masse ne peuvent pas être transposés aux cas de silos à vidange en cheminée. AbstractA part of the work developed with the CTICM for the « Mission Silo » is revea led in the paper. This part regroups two main subjects. On the one hand, the different flow pat terns which appear during discharge are analysed by the determination of the velocity profile in small-scale model silo. On the other hand, the comparison between experimental results of the wall pressure and the calculus wiht Wal ter's method, SOKOL's method and the norm DIN, is developed. This analysis shows that all the theoretical methods related to the mass flow are not veri fied for the funnel flow silo.• 54600 Villers-lès-Nancy.

A theory for pressures in cylindrical silos under concentric mixed flow

“…However, these authors did report that horizontal overpressures in the order of two have been observed for silos which exhibit an effective transition (e.g. Khelil, 1989;Khelil and Roth, 1990). It will be shown in what follows that the discharge overpressure predictions of the mixed flow theory are commensurate with observations from these and other past experiments (e.g.…”

Gravity mass powder flow through conical hoppers ‐ Part II: A mathematical model predicting the axial and radial profiles of normal stresses from flow velocity measurements

“…Contrary to Newtonian fluids, these two orthogonal stresses are not equal, and they are linked by a Janssen coefficient defined in the present work as k j [ 1,2 ] : These two normal stresses are presented in Mohr's circle; the vertical stress is presented as a major principal stress, and the small stress (horizontal stress) is a minor principal stress. Thus, k j is the ratio of the major and minor principal stresses; its value can be measured using shear testers (eg, an FT4 powder rheometer) as a function of internal angle friction as follows [ 3,4 ] : The analysis of the principal stresses inside cylindrical and conical hoppers is based on the Janssen model applied to the static or dynamic states of the granular system inside cylindrical hoppers. This model indicates that, for a shallow powder bed, the normal stresses are quasi‐equivalent to the static pressure of fluids, which is a linear function of powder depth.…”

A theory for pressures in cylindrical silos under concentric mixed flow

“…However, these authors did report that horizontal overpressures in the order of two have been observed for silos which exhibit an effective transition (e.g. Khelil, 1989;Khelil and Roth, 1990). It will be shown in what follows that the discharge overpressure predictions of the mixed flow theory are commensurate with observations from these and other past experiments (e.g.…”