Glossary of Pneumatic Conveying Terms
abrasiveness – The ability of a particle to cause wear on a contact surface. This quality is determined by its hardness factor and sharpness of the points of contact. The actual degree of wear then depends on power factors of both the contact pressure and the relative velocity of the contact surface. hard, sharp, angular-shaped particles may be expected to be highly abrasive.
absorption – 1. Penetration of a substance, usually a fluid, into the body of another. 2. The attachment of water molecules to the surface of particles.
adhesion – Resistance to separation between two unlike materials under zero applied normal pressure.
aeration – The action of injecting gas, usually air, to a bulk material to weaken the particulate structure by dilation. The process induces the material to adopt a fluid or highly agitated state.
agglomerate – An accumulated cluster of many particles that are rigidly bonded together by inter-particle forces, partial fusion, sintering, or by growing together, such that they act as a single, larger particle.
‘angel hairs’ – Long thin ‘streamers’ that are formed in the lean phase handling of low melting point granules, such as plastics, due to the high velocity frictional contact of the particles on the pipe walls melting the particle surface and forming extended length of narrow thin films or fibres that become entangled in the subsequent bulk.
attrition – Unwanted reduction in particle size caused by the collision of particles with other particles or with a surface, resulting in abrasion, causing fines, or fracture that creates “mother” and “daughter” particles.
bin – A bulk storage container, usually of small or medium size. Synonymous with “hopper” and to a limited extent “silo.” May be mobile or transportable.
bin activator – A device for stimulating discharge from a bulk storage container by vibrating a base conical bowl section that has a conical convergence to the outlet neck. This section is supported from the bin walls by a number of links having flexible end fittings. The rim of the bowl is connected to the outlet of the main bin by a flexible skirt. Within the
bowl is a concentric inverted cone to shield the outlet and create an annular flow gap.
bridging – The formation of arches of particles keyed, jammed or cohered together across the pathway of flow to form a stable obstruction.
bulk – A mass of particles
bulk density – The mass of a quantity of bulk material divided by the total volume that it occupies under defined conditions of preparation. See apparent powder density, loose poured density, tapped density, compacted density.
cavitation – The Formation of a cavity
choking – The phenomenon of the formation of a slugging, fluidised bed forming in a vertical section of a pneumatic conveying line as the gas velocity falls below the level at which it can entrain the solids.
deliquescent – The ability to absorb moisture from the atmosphere, to the extent that the product dissolves in the absorbed fluid.
feeder – A device used to discharge a bulk storage container in a controlled manner. Typical equipment for this purpose are screw feeders, belt conveyors, vibratory feeders, and rotary valves.
FIBC – A Flexible Intermediate Bulk Container
flow – Plastic deformation of a bulk material, due to the influence of external forces.
flowability – A expression is cited as a measure of how easily a material will flow.
fluid – A liquid or gas
fluid bed – A suspension of particles suspended in an upward flow of fluid (or downward flow if the particles are less dense than the fluid). The bed may be quiescent or boiling, according to the quantity of the fluidizing fluid.
fluidization – A condition of zero internal strength of a powder bed brought about by the presence of excess fluid, usually air, in the interstitial voids of a fine bulk solid that dilates the bulk sufficiently to offer the constituent particles unrestrained freedom for rearrangement and hence behave like a fluid of low viscosity.
fluidised flow – The pouring or otherwise causing to move of fluidised solids under the influence of gravity or pressure gradient.
fly ash – Finely divided ash composed of fused silica and glass, collected from electrostatic precipitators of power stations burning pulverized coal.
free flowing of bulk material – A particulate solids that offers no cohesive or rigid structural resistance to deformation under gravity flow.
friability – The tendency of particles and granules to break down in size during handling and storage under the influence of light physical forces.
funnel flow – the characteristic funnel shape flow pattern having a composite form. This comprises of a core flow channel, formed by a narrow cross section of flow emanating from the outlet, that is replenished by a drained repose
surface. The term is often utilized to generically describe all flow patterns that are not mass flow.
hardness – Hardness is characterised, in general, by the resistance of a material to deformation. This property reflects a material’s susceptibility to abrasion by other material of contact and its ability to abrade other
materials. As such, the value is a measure of its resistance to wear and aggressiveness to cause wear on other materials. When the surface is sufficiently large, absolute hardness is normally measured by determining the resistance to indentation, as in Brinell, Rockwell, Vickers diamond pyramid and scleroscope hardness tests. For particles and powders hardness, it is generally described in relation to its capacity to scratch or wear other materials, without itself suffering surface degradation. Ten materials of different hardness are defined by Mohr’s scale of hardness, to act as a basis for comparison and interpolation.
hopper section – The converging section of a bulk storage container leading to the outlet. Often cone-shaped from a cylindrical hopper and pyramid-shaped from a rectangular hopper.
hydrophilic – the property that defines a material as attracting water. Water exhibits an obtuse contact angle with hydrophilic materials.
hydrophobic – The property that defines a material as water repellent. Water exhibits an obtuse contact angle with hydrophobic materials. This property favors the use of such materials, for example, sheets of ultra-high molecular density polyethylene, as contact surfaces for damp wet bulk products, to minimize the wall cohesive effects of surface tension.
hydrostatic pressure – A state of stress in which all the principal stresses are equal (there is no shear stress), as in a fluidized powder where the pressure in the voids is due to the head of product and acts in all directions.
laminar flow – Flow in which the head loss is proportional to the first power of the velocity. It is characterised by the lack of turbulence.
mass flow – A flow pattern in which the entire contents of storage are mobilized to flow when discharge takes place from a bulk storage container. It is characterized by the fact that no stagnant zones are present during discharge when flow is fully mobilized. Slip essentially occurs on all wall contact surfaces.
mean particle size – Dimension of a hypothetical particle such that, if the total mass of the particulate system was wholly composed of such identical particles, they would all have that dimension.
particle – A discrete piece of matter.
particulate – Consisting of particles.
pellet – An agglomerate of particles produced by specialized techniques, such as pressing.
powder – A bulk solid consisting of particles less than 1mm
rathole – The void left when a core flow pattern or pipe evacuates all the material in the flow channel, to leave a stable unconfined surface.
shear failure – The permanent disturbance of a particulate structure by the application of a shear stress.
silo – A bulk storage container, usually of large volumetric capacity and tending to have a slender, cylindrical body section with a conical hopper section. Broadly synonymous with “hopper” and, to a limited extent, with “bin.”
suspension – A dispersion of particles in a fluid.
ullage – The space in the upper part of a bulk storage container that cannot be filled because of the surface contours formed by the repose conditions acting from the point of fill.
wet scrubber – A dust collecting system that employs a spray system to capture particles.
Source: Glossary of Terms in Powder and Bulk Technology, The British Materials Handling Board
