Since decrease in Hausner ratio(HR) means increase in flow-ability of powder. Does it means when HR increases , it will be easy to compress(since flow ability is decreasing,) and will form better pellets (better cohesiveness). How do I explain the increasing trend of HR with increasing temperature of treated biomass?
Dear Hari,
As you know, Hausner ratio isn't an absolute property of a material. It is a property of the powder of a material with a given particle size, particle size distribution, and particle shape which is processed via a given processing method. These factors depends on the methodology used to prepare and process the powder. Based on that, one must be careful when he/she wants to use Hausner ratio for comparison purposes.
Hence, Hausner ratio can be used to compare (i) two processing methods for the same powder, (ii) two powders, of the same material, with the same processing methods, and (iii) so on as the degree of freedom of the experiments is one only.
Keeping the above in mind, Hausner can be used as an indicator for the compressibility as it is related to "Carr Compressibility Index" which, as the name suggests, indicates the compressibility of the powder.
Remember:
Carr Compressibility Index = 100 (Vo - Vf) / Vo
Hausner Ratio = Vo/Vf
where:
Vo = original bulk volume of powder
Vf = final tapped volume of powder
The flowability cannot tell you the compressabilty though it always needs to balance free flow with better cohesiveness (high green strength) and ease compression.
Increasing HR means worse flowability. It indicates your heat treatments make the particle surface of the biomass more rough/sticky.
One can easily write down the following connection from the definition of C and H index numbers:
C= 100(1- 1/H), which is always positive definite number.
That means higher the Hausner number (i.e. , higher the densification) higher will be the Carr Compressibility index and poorer the flow ability.
As indicated Dr. Disher properly these numbers are not material properties but they depend on the size and geometry of the particles and their size distribution assuming that they are not exposed to any fluid wetting media, which due to low friction increases the both densification and Carr--index
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