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 (chemistry), cohesion. Powder flowability depends on many traits: * the shape and size of the powder particles due to ...

of a

powder A powder is a dry 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 distinguish se ...

granular material A granular material is a conglomeration of discrete solid, macroscopic scale, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when granulation, grains collide). T ...

. It is named after the engineer Henry H. Hausner (1900–1995). The Hausner ratio is calculated by the formula ::

H=\frac

where

\rho_B

is the freely settled

bulk density In materials science, bulk density, also called apparent density, is a material property defined as the mass of the many particles of the material divided by the bulk volume. Bulk volume is defined as the total volume the particles occupy, includ ...

of the powder, and

\rho_T

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 - 1.4J. 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 (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. The ...

(C), another indication of flowability, by the formula

H=100/(100-C)

. 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 {{pharmacology-stub