DEM study in the critical height of flow mechanism transition in a conical silo

The discharging in silo presents the characteristics of mass flow in the upper part and funnel flow in the lower part. Obviously, there is a special position where the flow pattern transition occurs. To clarify the special position of flow pattern transition during discharging of rice particles in conical silos, by means of Discrete Element Method (DEM), the change in flow characteristics was analyzed in terms of the velocity, porosity and orientation of partides. Furthermore, the effects of silo geometry parameters on the special position were discussed. The results showed that the flow characteristics change significantly during the flow pattern transition, expressing as that velocity, porosity and particle orientation change respectively from uniform to uneven, small to large and horizontal to vertical. Based on these variations, the special position of flow pattern transition is defined as the critical height and can be determined by a special change rate of velocity. Moreover, the critical height increases with increasing hopper half angle or silo diameter, while it remains nearly constant first and then decreases with the increase in outlet size. Finally, the mathematical model between the silo geometry parameters and the critical height was established. Overall, the results are useful for understanding the change in flow characteristics of rice particles during discharging and further provide guidelines to the appropriate design of conical silos. (C) 2018 Elsevier B.V. All rights reserved.