Quantitative and comparative study of the effect of drainage mode on solids flow pattern in MPBAC by whole-field residence time distributions

Rate-controlled drainages of particles are sometimes necessary in manufacturing since the predetermined proportioning of different raw materials is guaranteed by different rates of feeding and discharging. Cumulated pebbles outside silos yield forces on particles inside silos during rate-controlled drainage, promoting potentially different characteristics of solids flow pattern (funnel or mass flow) from that of free discharge. We performed the rate-controlled drainage experiments for Line or Circular silos with different sizes and inclination angles with the PTV-equipped MPBAC (Monolayer Pebble Bed with Adjustable Configuration). These factors' effects on solids flow patterns for the two drainage modes are analyzed qualitatively and quantitatively. We find that nearly all rate-controlled cases present a narrower main flow compared with free discharge, indicating the more difficult occurrence of mass flow. To obtain mass flow, increasing the outlet's inclination angles and adopting Line outlets are more effective compared with increasing outlet sizes.