Definition of Flow Properties:
The ability of powder particles to flow under gravity or mechanical force.
Factors Affecting Flow:
Particle Size: Fine particles (<100 µm) often have poor flow.
Shape: Irregular shapes interlock, hindering flow, whereas spherical particles flow more easily.
Moisture Content: Hygroscopic drugs absorb water, leading to cohesion and reduced flow.
Measurement Methods:
Angle of Repose: Measures the maximum angle at which powder can be piled without collapsing.
Bulk and Tapped Density: Determines compressibility and flowability.
Hausner Ratio and Carr’s Index: Evaluate flowability based on bulk and tapped density differences.
Importance:
Critical for ensuring uniform mixing, dose accuracy, and smooth manufacturing processes.
Angle of Repose
Angle of Repose is the maximum angle at which a material (such as powder or granules) remains stable without sliding or collapsing.
It measures the flowability of powders—lower angles indicate better flow properties.
Formula:
Where:
θ = Angle of repose (in degrees)
h = Height of the cone formed by the material
r = Radius of the base of the cone
Significance:
θ<30: Excellent flow.
30∘−40∘: Good flow.
>40∘>: Poor flow.