Elutriation
Encyclopedia
Elutriation, also known as air classification, is a process for separating lighter particles from heavier ones using a vertically-directed stream of gas
or liquid
(usually upwards). This method is predominately used for particles with size (>1μm). The smaller or lighter particles rise to the top (overflow) because their terminal velocities
are lower than the velocity of the rising fluid. The terminal velocites of any particle in any media can be calculated using Stokes' Law
if the particle Reynolds number is below .2.
Material may be separated by means of an elutriator, which consists of a vertical tube up which fluid is passed at a controlled velocity. When the particles are introduced, often through a side tube, the smaller particles are carried over in the fluid stream while the large particles settle against the upward current. If we start with low flow rates small less dense particle attain their terminal velocites, and flow with the stream. The particle from the stream is collected in overflow and hence will be separated from the feed. Flow rates can be increased to separate higher size ranges.
Further size fractions may be collected if the overflow from the first tube is passed vertically upwards through a second tube of greater cross-section, and any number of such tubes can be arranged in series
It is used in mineral processing for size classification.
The Elutriation Dust Value is also a usual measure for quantification of dust, generated by testing wherein mechanical forces such as vibration are applied to granules of e.g. a detergent agent.
Elutriation is a common method used by biologists to sample meiofauna. The sediment
sample is constantly agitated by a flow of filtered water from below, the action of which dislodges interstitial organisms embedded between sediment grains. A very fine filter at the top captures these organisms from the overflow.
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
or liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
(usually upwards). This method is predominately used for particles with size (>1μm). The smaller or lighter particles rise to the top (overflow) because their terminal velocities
Terminal velocity
In fluid dynamics an object is moving at its terminal velocity if its speed is constant due to the restraining force exerted by the fluid through which it is moving....
are lower than the velocity of the rising fluid. The terminal velocites of any particle in any media can be calculated using Stokes' Law
Stokes' law
In 1851, George Gabriel Stokes derived an expression, now known as Stokes' law, for the frictional force – also called drag force – exerted on spherical objects with very small Reynolds numbers in a continuous viscous fluid...
if the particle Reynolds number is below .2.
Air Elutriation
An air elutriator is a simple device which can separate particles into two or more groups.Material may be separated by means of an elutriator, which consists of a vertical tube up which fluid is passed at a controlled velocity. When the particles are introduced, often through a side tube, the smaller particles are carried over in the fluid stream while the large particles settle against the upward current. If we start with low flow rates small less dense particle attain their terminal velocites, and flow with the stream. The particle from the stream is collected in overflow and hence will be separated from the feed. Flow rates can be increased to separate higher size ranges.
Further size fractions may be collected if the overflow from the first tube is passed vertically upwards through a second tube of greater cross-section, and any number of such tubes can be arranged in series
It is used in mineral processing for size classification.
The Elutriation Dust Value is also a usual measure for quantification of dust, generated by testing wherein mechanical forces such as vibration are applied to granules of e.g. a detergent agent.
Elutriation is a common method used by biologists to sample meiofauna. The sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
sample is constantly agitated by a flow of filtered water from below, the action of which dislodges interstitial organisms embedded between sediment grains. A very fine filter at the top captures these organisms from the overflow.
See also
- Air classifierAir classifierAn air classifier is an industrial machine which sorts materials by a combination of size, shape, and density. It works by injecting the material stream to be sorted into a chamber which contains a column of rising air...
- N.N.Zoubov Engineers SMCE Air Classifier / Air Separator - How Works.