Finite element model development and validation for incipient flow analysis of cohesive powders from hopper bins

A true (cubical) triaxial tester was built to evaluate the modified Cam-cla y parameters for wheat flour [1]. A finite element model (FEM), using the m odified Cam-clay equations, was used to predict incipient flow behavior of wheat flour in a mass flow hopper bin. The incipient flow regime in a hoppe r bin was characterized by the formation of the first dynamic arch. The fir st dynamic arch represented the transition between the static case, before opening the hopper outlet, and the dynamic case, when the powder was flowin g out of the hopper. Experimental observation showed that an arch was forme d after minimal discharge when the gate of a mass flow hopper bin was opene d. This arch broke before the development of fully dynamic powder flow. To validate the FEM, a transparent plastic laboratory size mass flow hopper bi n with an outlet size of 203 mm and a hopper angle of 15 degrees with respe ct to the vertical was used. The first experimentally observed dynamic arch location and profile were used to validate the finite element model predic tions. Mean average relative difference (ARD) between the FEM predicted and the mean of the first experimentally observed dynamic arch location and pr ofile was 14.2% and the mean absolute difference was 5.8 mm. The FEM predic tions were within the 95% CI of the measured values. (C) 1999 Elsevier Scie nce S.A. All rights reserved.