A proposed predictive methodology for the evaluation of caking effect on different types of commercial sugars

Abstract

This paper presents preliminary results of an alternative experimental methodology under development to predict the caking effect often observed in bulk solids after time storage. This methodology is based on 1) the principle that the particle is sheared after the shear stress overcome a maximum value; 2) the maximum shear stress depends on the particles physical properties and their chemical nature; 3) Prorating is a well-known and often used empirical procedure to minimize the scatter at shear tests; and 4) that the static friction coefficient depends on particle-particle contact time and could be described by the phenomenological state-and-rate model formulated by Dieterich, Rice, and Ruina. The proposed methodology aims to evaluate the increasing of the static coefficient of friction with rest time, through “stop-and-go” shear experiments and according to Dieterich, Rice and Ruina model. Finally, the increase in shear stress with time is used to extrapolate the instantaneous yield locus into a predicted time yield locus, using the prorating technique We tested four types of commercial sugar and the results of time yield locus, obtained from experiments, have seemed similar to those predicted using the proposed methodology. We obtained satisfactory results for the short rest times tested in this preliminary study, which could be extended to long periods.

Keywords:
Sugar; Granular shear; Time yield locus; Prorating, caking