Rheological properties characterization of powders for flour and sugar powders and hopper design

Abstract

The present work experimentally studies the rheological behavior of two materials commonly used in the food industry using two powder rheometers. The Anton Paar MCR 302e rheometer equipped with a powder cell was one of the two devices used. A second rheometer, a specific unit powder rheology device manufactured by Freeman Technology (FT4) was used to measure non-aerated powder. Two different powders from the food industry were chosen to carry out the comparison: sugar and flour. Wheat flour is a highly cohesive material, classified as Geldart C particles, the test of which are strongly conditioned by the previous pre-compaction of the sample. Sugar was chosen because it is a complex cubic geometry, being different from that of most particles, which are spherical. Compressibility parameters, such as bulk density or Hausner ratio, cohesion strength, wall friction parameters and warren spring cohesion were measured. This work conducts an in-depth study of rheological behavior based on the morphology of the particle, which was measured with a Malvern microscope (Morphologi4). Cohesive strength results show that wheat flour is twice as cohesive as sugar. In addition, the square morphology and large size of the sugar particles greatly influence several parameters and can be quantified in terms of energy expended with the downward movement of the blades by up to 100 mJ more than in the case of flour. Depending on the measurement methodology, differences in the hopper angle of \(11\,^\circ \) and \(31\,^\circ \) are observed.

Graphical abstract