Powder flow and storage - Chapter 10
Powder discharge types from a silo
The videos in two links below illustrate common flow types that can occur for solids discharging from the hopper section of a silo, they both open in a new web tab.Please note that Funnel Flow is another name for Core Flow, and in the video the Discrete Element Method (DEM) has been used to illustrate the flow and various other important aspects of powder flow within the silo. Please watch the video to the end - the funnel flow is nicely illustrated near the end in 3D.
The design of hoppers is to ensure that "arching" of the solids above the outlet does not occur.
Reliable flow can be achieved with various hopper inserts, including fluidisation. However, care needs to be taken to avoid a "powder avalanche", which may cause uncontrolled flow of a powder within the process and is highly dangerous. This video illustrates a hopper insert that fluidises the particles to prevent interlocking and the formation of an arch. The process of arching is also illustrated.
Other techniques to disrupt arch formation include: mechanical shock on the outside of the hopper (manual or automated); an inverted cone inside the silo near the top of the hopper section to direct the powder flow to avoid arch formation; and careful environmental control to avoid humidity levels that may lead to particles sticking. For materials stored for any length of time in a silo, it is also common practice to recirculate material from, and back to, the silo periodically to prevent "time consolidation" of the material.
Answers to problems
Answer to problem 12, on a spreadsheet.FAQ