Effects of process parameters and hopper angle on segregation of cohesive ternary powder mixtures in a small scale cylindrical silo

Abstract

Segregation of two ternary powder mixtures at filling and at discharge of a 0.4m3 cylindrical silo has been investigated experimentally. The material distribution at silo filling was determined by sampling from the upper layers of the heap at different radial positions and with varying levels of fill. Discharge flow patterns were elaborated with tracer objects in the majority of experiments and the composition of the bulk solids during emptying was determined by sampling across the entire discharge stream. The effects of free fall distance and intermittent discharge and filling on segregation at filling as well as the effect of hopper angle on segregation at discharge were investigated. Furthermore, the influence of filling rate is discussed. Based on the results, side-to-side segregation with accumulation of fine particles to the silo walls clearly increases with increasing free fall distance. Segregation is also aggravated in situations where the silo is filled and discharged intermittently, because the shape of the powder bed’s surface changes when a portion of the silo contents is withdrawn. The effect of filling rate remains unclear and should be more deeply investigated in the future. The hopper angle determines the discharge flow pattern, i.e., funnel or mass flow, but the composition of the powder mixture towards the end of complete emptying is mainly determined by the material distribution at the levels of fill that are withdrawn last. The presented findings increase the understanding of the effect of process parameters and silo design on segregation, and can be used for mitigating the detrimental effects of segregation of bulk solids handled in silos.