Hausner ratio

The Hausner ratio is a number that is correlated to the flowability of a powder or granular material. It is calculated by the formula

:: $H=frac{
ho_T}{
ho_B}$

where $ho_B$ is the freely settled bulk density of the powder, and $ho_T$ 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 [R.O. Grey and J.K. Beddow (1969) "On the Hausner Ratio and its relationship to some properties of metal powders" "Powder Technology", Vol.2, No.6, pp 323-326.] [Q. Li "et al" (2004) "Interparticle van der Waals force in powder flowability and compactibility" "International Journal of Pharmaceutics", Vol.280, Iss.1-2, pp 77-93.] [C. Conesa "et al" (2004) "Characterization of Flow Properties of Powder Coatings Used in the Automotive Industry" "Kona", Vol.22, pp 94-106.] [S.L. Rough, D.I. Wilson and D.W. York (2005) "Effect of solids formulation on the manufacture of high shear mixer agglomerates" "Adv. Powder Technol"., Vol.16, pp 145-169.] [R.A. Garcia, R.A. Flores and C.E. Mazenko (2007) "Factors contributing to the poor bulk behavior of meat and bone meal and methods for improving these behaviors" "Bioresource Technology", Vol.98, No.15, pp 2852-2858.] as an indication of the flowability of a powder [USP <1174> "Excipient General Information Chapter: Powder Flow] . A Hausner ratio greater than 1.25 is considered to be an indication of poor flowability. The Hausner ratio (H) is related to the Carr index (C), another indication of flowability, by the formula $H=100/(100-C)$ . Both the Hausner ratio and the Carr index are sometimes criticized because their relationships to flowability were established empirically and do not have 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.

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