Granular materials hopper flows

W. Reisner. The behaviour of granular materials in flow out of hoppers. Powder Technology, l(5) 257-264,1968. 

Whitaker, S. (1969). Advances in Theory of Fluid Motion in Porous Media. I EC., 61,4. Zeininger, G. and Brennen, C. E. (1985). Interstitial Fluid Effects in Hopper Flows of Granular Materials. ASME Cavitation and Multiphase Flow Forum, Albuquerque, N. Mex. 

The onset of powder motion in a hopper is due to stress failure in powders. Hence, the study of a hopper flow is closely related to the understanding of stress distribution in a hopper. The cross-sectional averaged stress distribution of solids in a cylindrical column was first studied by Janssen (1895). Walker (1966) and Walters (1973) extended Janssen s analysis to conical hoppers. The local distributions of static stresses of powders can only be obtained by solving the equations of equilibrium. From stress analyses and suitable failure criteria, the rupture locations in granular materials can be predicted. As a result, the flowability of granular materials in a hopper depends on the internal stress distributions determined by the geometry of the hopper and the material properties of the solids. 

Nguyen, T. V., Brennen, C. and Sabersky, R. H. (1979). Gravity Flow of Granular Materials in Conical Hoppers. Trans. ASME, J. Appl. Mech., 46,529. 

Relatively simple optical experimental techniques to study noncohesive particulate flow have also been developed, such as the polarized light probe system by Allersma (42,43). With this technique, the principal stress distribution and displacement of photoelastic granular material flowing in two-dimensional hoppers, with and without obstructions (distribution bars), can be obtained, as shown in Fig. 4.18. 

Computational mechanics, and in particular the DE method, may be successfully used to analyze a wide range of operations involving powders and granular materials. Of particular relevance in a pharmaceutical context are applications related to flow of powders in hoppers (66), fluidized beds (67), and mixers (68,69). The method has been applied in the analysis of ball mills (70) and may be used to look more deeply into certain processes such as vibration-induced size segregation of granular materials (71) and packing (72). 

The feed hopper feeds the granular material to the extruder. In most cases, the material will flow by gravity, unaided, from the feed hopper into the extruder. Unfortunately, this is not possible with all materials. Some bulk materials have very poor flow characteristics and additional devices may be required to ensure steady flow into the extruder. Sometimes this can be a vibrating pad attached to the hopper to dislodge any bridges as soon as they form. In some cases, stirrers are used in the feed hopper to mix the material (and prevent segregation) and/or to wipe material from the hopper wall, if the bulk material tends to stick to the wall. 

Wassgren, C.R. Hunt, M.L. Freese, P.J. Palamara, J. Brennen, C.E. (2002) Effects of vertical vibration on hopper flows of granular material. Physics of Fluids 14, 3439-3448. 

Williams, J.C. (1977) The rate of discharge of coarse granular materials from conical mass flow hoppers. Chem. Eng. Scl, 32(3), 247-255. 

Commercial sensors are used to measure pressure, strain, acceleration, and sound propagation. These sensors are usually mounted on walls of granular experiments, for example, on hoppers [142] and shear cells [183]. However, there are sensors developed in the late 1950s, which can be placed into a granular material and report measurements wirelessly. The "rf-pill" was developed for medical applications [353-357] to measure the pressure in the digestive tract. The rf-pill is a small transmitter and sensor, which has been used to measure stress in vertical tube flow [158] and pressure in hopper discharge [128,133]. 

R.M. Nedderman, U. Tiizun, S.B. Savage, and G.T. Houlsby. The flow of granular materials-i Discharge rates from hoppers. Chemical Engineering Science, 37(11) 1597-1609, 1982. 

G.C. Gardner. The region of flow when discharging granular materials from bin-hopper systems. Chemical Engineering Science, 21(3) 261-273, 1966. 

M.F. Handley and M.G. Perry. Stresses in granular materials flowing in converging hopper sections. Powder Technology, 1(5) 245-251,1968. 

R.L. Michalowski. Flow of granular material through a plane hopper. Powder Technology, 39(l) 29-40, 1984. 

Bin Activator n A device that promotes the steady flow of granular or powdered plastics from storage bins or hoppers. Among the many types of equipment are vibrators or mallets acting upon the outside of the container, prodding devices or air jets acting directly on the material, inverted-cone baffles with vibrating means located at the bottom of the hopper, and other live bottom devices such as scrapers, rolls, and chains. 

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