Flowability is a vital bulk powder characteristic. The term Flowable means an irreversible deformation of a powder to make it flow due to external energy or force application.
Various parameters such as Carr index or Carr Compressibility Index and Hausner ratio are used to express flowability of powders.
The Carr Compressibility Index and the Hausner Ratio are two measurements that can be used to estimate the propensity of a given powder sample to be compressed and are thought to indicate the significance of interparticulate interactions.
These interactions are often less relevant in the case of a free-flowing powder, when the bulk and tapped densities are close in magnitude. On the other hand, poorer moving materials are distinguished by increased interparticle interactions, resulting in a bigger disparity between bulk and tapped densities. The following relationships are used to calculate the two indexes.
Calculation formula of Carr Compressibility Index = 100 X [(Vo-Vf) / Vo]
Calculation formula of Hausner Ratio =Vo/Vf
Vo - Initial apparent volume
Vf - Final tapped volume powder after tapping the material until no further volume changes occur.
Another Formula for the calculation of the Carr Compressibility Index and Hausner Ratio is using the bulk density (Pbulk) and tapped density (Ptapped) as follows:
Calculation formula of Carr Compressibility Index = 100 X [(Ptapped-Pbulk) / Ptapped]
Calculation formula of Hausner Ratio = Ptapped / Pbulk