Effect of outlet diameter of cone-in-cone insert on silo flow pattern

Abstract: In the food, chemical, pharmaceutical and other industrial engineering field, about 50% of the products and 75% of raw materials are usually stored in the form of particles in the silo. The silo flow pattern can be divided into the mass flow and the funnel flow. In the process of silo design, the mass flow pattern is preferred. With the appropriate presence of cone-in-cone insert, the funnel flow pattern can be changed into mass flow pattern in funnel flow silo. In order to understand the effect of structure and position parameters of cone-in-cone insert on the flow pattern and develop a theory model to design them properly, the discharging processes of acrylonitrile butadiene styrene copolymer (ABS) beads in scale-down funnel flow silo were simulated using the discrete element method (DEM). The validity of the DEM simulations was confirmed by comparing with the experimental results. Mass flow index (MFI) was used to judge silo flow pattern. Firstly, the effects of the height of cone-in-cone insert, the distance between outlet of cone-in-cone insert and discharge outlet of silo and the angle of cone-in-cone insert on the flow pattern were studied. The simulation results revealed that when the outlet diameter of cone-in-cone insert was equal to the discharge outlet diameter of silo and the angle of cone-in-cone insert was less than 120°, the funnel flow pattern could not be changed into the mass flow in silo, and MFI increased with the increase of the height of cone-in-cone insert and the distance between outlet of cone-in-cone insert and discharge outlet of silo. Then, the effects of the outlet diameter of cone-in-cone insert on the flow pattern and the pressure on the silo wall were analyzed. The results showed that with the decrease of the outlet diameter of cone-in-cone insert, the MFI increased and the funnel flow could change into the mass flow in funnel flow silo. The maximum compressive force on the silo wall was reduced and the compressive force was evenly distributed on the silo wall with the appropriate presence of cone-in-cone insert in silo, and the maximum pressure on the silo wall decreased and the position of maximum pressure moved gradually to the silo transition zone with the decrease of the outlet diameter of cone-in-cone insert. In order to ensure the design effectiveness and installation stability of the cone-in-cone insert, the distance between outlet of cone-in-cone insert and discharge outlet of silo and the height of silo should not be larger than the height of silo conical surface. Based on the simulation results, the smaller value of the outlet diameter of cone-in-cone insert was preferred when it was greater than 6 times of the maximum diameter of particle in silo, the larger value of the angle of cone-in-cone insert was preferred when it was less than the angle of silo conical surface, and the ratio of the distance between cone-in-cone insert and silo conical surface to the outlet diameter of cone-in-cone insert should be equal or larger than 1 when the discharge outlet diameter of silo was constant. These design criteria should be abided to ensure mass flow pattern in mass flow silo. The research results provide reference for determining the structure and position parameters of cone-in-cone insert in engineering.