The field of powder and bulk solids storage, handling, and processing has a unique terminology. Here are some of the most important terms and their definitions.
Arching: A no-flow condition in which material forms a stable arch (bridge) across the bin
Attrition: The generation of fines or dust during solids handling. Highly sensitive solids prone to attrition include fragile granules (kitty litter), finished food products (chips), plastic pellets, and sugar or salt.
Bin: Container for bulk solids with one or more outlets for withdrawal, either by gravity alone or by flow-promoting devices which assist gravity
Bridging: Same as arching (a no-flow condition)
Bunker: Same as bin, often used in reference to storing coal
Chute: Means of collecting material which, unlike a hopper, does not operate full
Cylinder: Vertical part of a bin which has a constant cross-section; can be any shape
Dense phase conveying: This occurs when particles are conveyed in the gas stream at a velocity that is less than the saltation velocity. Two general modes of flow can result in dense phase, and are referred to as plug or piston flow and moving bed (dune) flow.
Dilute phase conveying: This occurs when particles are conveyed in the gas stream at a velocity that is greater than the saltation and choking velocities.
Discharger: Device used to enhance material flow from a bin but which is not capable of controlling the rate of withdrawal
Effective head: Convenient way to express consolidating pressure by dividing it by bulk density
Elevator: Same as bin, often used in reference to storing grains
Expanding flow: Flow pattern that is a combination of mass flow and funnel flow
Feeder: Device for controlling the rate of withdrawal of bulk solid from a bin
Flooding, flushing: Condition where an aerated bulk solid behaves like a fluid and flows uncontrollably through an outlet or feeder
Flow channel: Space in a bin through which a bulk solid is actually flowing during withdrawal
Flow properties test report (FPTR): Jenike & Johanson’s bulk material characterization report typically containing results for a material’s cohesive strength, bulk density range, coefficient of sliding friction against hopper wall surfaces, moisture content, particle size distribution, and permeability. These are the core characteristics needed to properly design a mass flow bin and feeder.
Fluidization: Using air or inert gas to fully aerate a fine bulk solid to allow it to behave as a liquid
Funnel flow: Flow pattern in which solid flows in a channel formed within stagnant material
Hopper: Converging part of a bin
Mass flow: Flow pattern in which all solid in a bin is in motion whenever any of it is withdrawn
Pickup velocity: This is the gas velocity at the pick up point of the conveying system where solids are introduced into the conveying gas stream.
Piping: Same as ratholing
P-FACTOR: The ratio of the applied solids compacting pressure to the solids pressure during steady gravity flow
Ratholing: A non-flowing condition in which material forms a stable vertical hole within the bin
Saltation velocity: The gas velocity at which particles fully suspended within a horizontal conveying line begin to drop out of suspension and settle in a layer on the bottom of the pipeline.
Segregation: Separation of bulk solids by their size, shape, or particle density
Silo: Container for bulk solids with one or more outlets for withdrawal, either by gravity alone or by flow-promoting devices which assist gravity
State diagram: The plot of pressure drop as function of conveying gas velocity over range of solids loading. This diagram defines conveying modes of dilute and dense phase transport.