| The bulk behaviors of mustard seed, cracked wheat, sand, and wheat flour were experimentally evaluated at three relative humidity conditioning levels using a variety of standardized and adapted characterization techniques, in order to quantify the flow behavior of these granular materials under well defined conditions. The flow behavior of these granular materials will be specifically discussed in the context of a standard bulk solids process, the mixing of dry granular materials. The four granular materials chosen for this study each represent one of the four flowability classifications defined in ANSI/CEMA Standard 550.;Standardized characterization techniques utilized in this study include: particle size distribution by sieving, analysis of moisture content by drying, aerated bulk density, tap density and angle of repose measurements by means of a Hosokawa Micron Powder Characteristics Tester, morphological characterization by image analysis, and the calculation of Hausner ratio and compressibility from bulk density measurements. Prior to the use of the Hosokawa Micron device, aerated bulk density and tap density measurements using standardized and accepted practices involving graduated cylinders yielded unacceptable variations, especially with highly cohesive granular materials such as wheat flour. Recommendations and techniques for reducing such variations are presented.;Adapted characterization techniques for this study include: shear measurements to establish Mohr-Coulomb failure criteria by means of an annular shear cell, penetration measurements to determine force vs. displacement profiles for several granular material preconditioning states, evaluation of stress relaxation within a granular material after penetration, analysis of bulk density uniformity within a column of granular material by means of a segmented cylinder, and the interaction between granular materials, a quasi-statically moving blade within a two tank designed for granular materials, and a statistical analysis of all data in order to identify correlations between characterization techniques and to identify techniques which are suitable for quantifying the relative flowability of granular materials. |
