Hoppers and silos
Mass flow and funnel flow
Also known as mass flow, funnel flow, first-in-first-out, first-in-last-out.
Mass flow and funnel flow describe the two principal bulk-solids discharge regimes from a hopper or silo.
Mass flow
All material in the vessel moves downwards uniformly during discharge. The first material in is the first material out (FIFO). Mass flow requires:
- A steep, smooth-walled discharge cone
- An outlet large enough to defeat any cohesive arching
- Material flow properties (low cohesion, free flow)
Mass flow gives predictable residence times, no stagnant zones and reliable discharge. It is the preferred design for any application where material ageing, segregation or quality control matter.
Funnel flow
A central column of material moves while the surrounding mass stagnates. The first material in becomes the last (or never) material out. Funnel flow happens by default in any hopper or silo that does not specifically achieve mass flow.
Funnel flow tolerates simpler vessel geometry but introduces all the classic problems: rat-holing, bridging, material ageing, mass-flow indicators that lie about how much usable material remains in the vessel.
Restoring mass-flow behaviour
Where re-design is impractical, sonic horns on the discharge cone can push a funnel-flow silo closer to mass-flow behaviour by keeping the previously-stagnant zones moving. This recovers usable storage volume and prevents the long-term consolidation that eventually destroys hopper performance entirely.
Related terms
Related terms
- HopperA hopper is an inverted-pyramid or conical vessel for storing and discharging bulk solids. Bridging and rat-holing are the universal failure modes; sonic horns are a clean, low-maintenance remedy.
- SiloA silo is a large vertical bulk-solids storage vessel. Cement, fly-ash, lime, biomass, fertilizer and food-powder silos all bridge and rat-hole; sonic horns are the leading flow aid.
- Rat-holingRat-holing is a flow pattern in which material discharges through a narrow vertical channel above the outlet, while the surrounding material remains stagnant and consolidates.
- Bridging (bulk-solids)Bridging (also arching) is the formation of a stable arch of bulk solids above the discharge outlet of a hopper or silo, stopping material flow. The universal failure mode of bulk-solids storage.
- Discharge coneThe discharge cone is the converging lower section of a hopper or silo. Cone angle and surface finish determine whether the vessel delivers mass flow or funnel flow.