Studies of Wheat Flow in an Experimental Hopper

Abstract

Abstract : The main purpose of this work was to design an experimental hopper and use it to study how hopper geometry and particle characteristics affect granular flow. The investigation was performed using both qualitative and quantitative observations. The qualitative study was conducted by taking and analyzing photos representing different observations of the flow. The quantitative part was concentrated on the effect of the hopper geometry, i.e., height, width, hopper half angle, and discharge size, on the discharge rate. The effect of two of the particle characteristics, size and moisture content, on the discharge rate was also investigated The photographic study revealed that particles located on the centerline above the hopper discharge move faster than other particles elsewhere in the hopper. Moreover, stagnant zones with different shapes were obvious adjacent to the walls for different hopper geometries. The shape of the free surface was observed to mainly decline at the center since the particles in this location are moving at a higher speed than those at the sides. Another effect of the different velocities and stagnant zone, initiated in the hopper, was to notice much more deformation in the flow lines at the center than those at the sides and near the walls In the quantitative study, the flow rate was found to be independent of the material head and the width of the hopper. A small effect of the particle size on the discharge rate was noticed, with the lower rate corresponding to the smaller particles. The increase in the hopper half angle was found to negatively affect the discharge rate, with lower flow rates obtained for larger hopper half angles. A critical angle was found after which the flow rate would be constant. A decrease in the discharge rate was noticed as the moisture content of the particles increased. A linear relationship was obtained after a critical point (13.90% moisture content), below which no effect of moisture content on the flow rate was observed. The angle of repose was found to increase linearly as the moisture content of wheat particles increased. On the other hand, particles with larger sizes were found to have smaller angles of repose. In all cases, the angle of repose was a good measure of the material's flowability, with higher discharge rates obtained for samples with lower angles of repose Further work would require studying the effect of different agricultural seeds and different ranges of moisture contents on the angle of repose and the flow rate. Moreover, using a camera with several seconds of exposure time is recommended for studying different shapes of the stagnant zones