Issue link: http://www.e-digitaleditions.com/i/883179
Hoppers with outlets of other sizes can be chosen to meet the process requirements. Obviously, hoppers with smaller outlets will have a lower maximum solids dis- charge rate. Less apparent is that if a smaller outlet is specified, the hopper walls may need to be steeper to allow mass flow as the angle of wall friction often increases with decreasing outlet size. Closing remarks Shear cell testers are frequently used by formulators to assess the flowability of powders. By using the fundamen- tal properties measured by shear cell testers, cohesive strength, effective angle of friction, compressibility, and wall friction, together with permeability measurements, formulations can be readily optimized to ensure that they can be handled reliably in feed hoppers, storage bins, and other vessels. T&C References 1. Jenike, A.W., Storage and Flow of Solids, Bulletin 123, University of Utah Engineering Station, 1964 (revised, 1976). 2. Jenike, A.W., Gravity Flow of Solids, Bulletin 108, University of Utah Engineering Station, 1961. 3. Arnold, P.C. and McLean, A.G. "An Analytical Solution for the Stress Function at the Wall of a Converging Channel", Powder Techn., 13, 255 (1976). 4. Arnold, P.C. and McLean, A.G. "Improved Analytical Flow Factors for Mass-Flow Hoppers", Powder Techn., 15, 276 (1976). 5. Johanson, K., "Successfully Dealing with Erratic Flow Rates", Powder Pointers, 3, A (2009). 6. Sperl, M., "Experiments on corn pressure in silo cells–translation and comment of Janssen's paper from 1895", Granu Matter, 8, 2, 59 (2006). Greg Mehos. PhD, PE, is an adjunct professor in the Depart- ment of Chemical Engineering at the University of Rhode Island, Kingston, RI 02881. Tel. 978 799 7311. He also is available for consulting. Mike Eggleston, Tristan Trautman, Matthew Freeman, and Nicole Stevens-Murphy are current or former chemical engineering students at the university. Tablets & Capsules October 2017 19 Figure 13 Bulk density of APAP-MCC-HPC blend with 0.2 percent fumed silica and 1.0 percent magnesium stearate Bulk density (kg/m 3 ) Major consolidation stress (kPa) 750 700 650 600 550 500 0 2 4 6 8 10 Figure 14 Wall friction of APAP-MCC-HPC blend that includes 0.2 percent fumed silica and 1.0 percent magnesium stearate on 304 stainless steel with 2B finish Major consolidation stress (kPa) Bulk density (kg/m 3 ) 0 1 2 3 4 5 5 4 3 2 1 0