Characterizing moist food-powder flowability using a Jenike shear-tester

A range of commercially-available crop seeds and food powders were tested using a Jenike shear-tester. At low normal loads, all the materials are found to change their strength characteristics regularly, with increasing moisture content resulting in higher values for shear stresses. However, under high normal loads, an opposite trend was observed for some materials, for which there is the potential of a lubricating effect to develop, resulting in unpredictable bed behavior in a silo. Low moisture contents reduced shear-stress oscillations occurring in the bed of dry material considerably. At higher moisture contents, an unacceptably long horizontal shear displacement was needed to establish steady-state shearing conditions. This may render the Jenike shear-tester inappropriate in the examination of powders of higher moisture content, especially those composed of easily deformable particles. NMR analysis proved that chemical composition of water surrounding the moistened seeds was changing during the time and that may affect the granular bed flow characteristics. (C) 2011 Elsevier Ltd. All rights reserved.