Hausner ratio

The Hausner ratio is a number that is correlated to the flowability of a powder or granular material. It is named after the engineer Henry H. Hausner (1900–1995).^[1][2]

The Hausner ratio is calculated by the formula

$H=\frac{\rho_T}{\rho_B}$

where $\rho_B$ is the freely settled bulk density 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 ^{[3][4][5][6][7]} as an indication of the flowability of a powder.^[8] 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, 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

1. Beddow, J. K. 1995. "Professor Dr. Henry H. Hausner, 1900–1995." Particle & Particle Systems Characterization 12: 213. doi:10.1002/ppsc.19950120411.
2. Podczeck, Fridun & Brian E. Jones, eds. 2007. Pharmaceutical Capsules. London: Pharmaceutical Press, p. 111.
3. 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.
4. 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.
5. C. Conesa et al. (2004) "Characterization of Flow Properties of Powder Coatings Used in the Automotive Industry" Kona, Vol.22, pp 94-106.
6. 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.
7. 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.
8. USP <1174> "Excipient General Information Chapter:‹ Powder Flow

General Bibliography

• Mark Gibson (2001). Pharmaceutical Preformulation and Formulation: A Practical Guide from Candidate Drug Selection to Commercial Dosage Form. Boca Raton: CRC Press. ISBN 1-57491-120-1.