- Flow properties describe how powders or granules move under force, critical for efficient processing in pharmaceutical and industrial applications.
- Good flow properties ensure uniform mixing, accurate dosing, and smooth manufacturing, reducing defects and improving product quality.
Definition:
- 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.
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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:
-
$\theta = \arctan\left(\frac{h}{r}\right)$
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.
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