The Hausner ratio is a number that is correlated to the
flowability
Flowability, also known as powder flow is a property that defines an ability of a powdered material to flow, related to cohesion.
Powder flowability depends on many traits:
* the shape and size of the powder particles due to intermolecular force, ...
of a
powder
A powder is a dry, bulk solid composed of many very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms ''powder'' and ''granular'' are sometimes used to distin ...
or
granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when grains collide). The constituents that compose gra ...
. It is named after the engineer Henry H. Hausner (1900–1995).
The Hausner ratio is calculated by the formula
::
where
is the freely settled
bulk density Bulk density, also called apparent density or volumetric density, is a property of powders, granules, and other "divided" solids, especially used in reference to mineral components (soil, gravel), chemical substances, (pharmaceutical) ingredients ...
of the powder, and
is the tapped bulk density of the powder. The Hausner ratio is not an absolute property of a material; its value can vary depending on the methodology used to determine it.
The Hausner ratio is used in a wide variety of industries as an indication of the flowability of a powder. A Hausner ratio greater than 1.25 - 1.4
[J. Cain (2002) "An alternative technique for determining ANSI/CEMA standard 550 flowability ratings for granular materials" ''Powder Hand. Proc'', Vol.14, No.3, pp 218-220.] is considered to be an indication of poor flowability. The Hausner ratio (H) is related to the
Carr index The Carr index (also: Carr's index or Carr's Compressibility IndexPodczeck, Fridun & Brian E. Jones, eds. 2007. ''Pharmaceutical Capsules''111.) is an indicator of the compressibility of a powder. It is named after the scientist Ralph J. Carr, Jr.
...
(C), another indication of flowability, by the formula
. Both the Hausner ratio and the Carr index are sometimes criticized, despite their relationships to flowability being established empirically, as not having a strong theoretical basis. Use of these measures persists, however, because the equipment required to perform the analysis is relatively cheap and the technique is easy to learn.
References
General Bibliography
*
Particulates
Pharmaceutics
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