Toward a Grand Challenge in Powder Flows: The Effect of Material Properties, Boundary Conditions and Shear Rate on Fluctuations and Stress Fields in Flowing Powders

Publication Reference: 
08-13
Author Last Name: 
Tardos
Authors: 
Professor Gabriel I. Tardos, Mr. Mehrdad Kheripour Langroudi
Report Type: 
FRR
Research Area: 
Powder Flow
Publication Year: 
2010
Publication Month: 
11
Country: 
United States

Executive Summary

This is the final report on work performed on the IFPRI project during the period September 2005 through October, 2010. The research is focused on the study of Powder Mechanics and the ultimate goal is to develop a quantitative description of active flows for a wide variety of powders. The study is centered on the slow, frictional and the dense, “intermediate” regimes of flow where both frictional and inertial effects are important. The novelty of the project is the study of a large range of materials and several flow geometries to gain meaningful insight. We report on a series of materials from simple (round beds) to complex (fine, odd-shaped, elastic and/or compressible), used in a shear cell of the Jenike type, an axial-flow Couette, a centripetal geometry characteristic of a “spheronizer” and a hopper flow with a moving discharge (characteristic of a tabletting device) to measure stresses and porosity (void fraction), and their fluctuations as a function of geometry and shear rate.

The development of constitutive model for the intermediate regime of flow was also undertaken. The axial-flow Couette device was used as a “rheometer” to characterize the flowability of powders, develop a constitutive equation and use it in a continuum theoretical model to predict flow patterns, velocity and porosity distributions and forces on boundaries such as stationary walls. The PI is collaborating with several groups of simulators (DEM and MDS) and mathematicians to implement these models and compare theoretical results to computations as well as develop a continuous model “in house” based on commercially available software (FLUENT) and applied to the “Speronizer” geometry. Good results are reporter for the “fast” Jenike cell (collaboration with the group of Professor Sundar Sundarasen of Princeton University, see section 3.3.3.), the Couette device, using a continuous-type theory emplying FeatFlow, a Finite Element (FE) model developed by a group of mathematicians at the University of Dortmund in Germany (Professor Stefan Turek, see Appendix A).