The morphological, flow and failure characteristics of fractionated natural bulk material : evaluation of flowability of fractionated powdered liquorice using a specially designed flowmeter : the particle morphology was assessed by computer image analysis and the failure properties by shear cell testing
With the technological development in biologically orientated industries more and more natural products in powdered form are being handled and processed. Three differently comminuted liquorice rhizome products were classified into 23 narrow size fractions to investigate the particle and bulk characteristics of the material, and to study the influence of particle shape on powder flowability. The morphology of the fibrous particulate was investigated by using a Quantimet 720 Image Analyser. The perimeter (P), projected area (A), breadth (B), length (L), horizontal and vertical projected lengths (P V and Pi) and the horizontal and vertical Feret diameters (FV FH) were measured from which four dimensionless shape factors were evaluated, [P2/47rA, PHxPV/A, L/B, FV/FH]. The surface texture of the particles was measured by fractal analysis. The influence of particle shape and size on the mean flow rate, coefficient of flow variation and flow uniformity were measured using a specially designed inclined tube flowmeter. The failure properties of powdered liquorice when sheared under known normal compressive stresses were measured and from a series of yield loci the unconfined yield strength, major consolidation stress and effective angle of internal friction were obtained. The effects of particle shape and size on the angle of internal friction, wall friction, bulk and packed densities were. investigated and the experimental correlations expressed in terms of mathematical equations. These relationships, together with the failure function plots, indicate that comminuted liquorice powder behaves as a "simple" powder.