flowability

Flowability is the ease with which a material moves or flows under gravity or applied stress. It is a key property for powders, granular solids, pastes, and slurries, and it influences bulk handling, storage, dosing, mixing, filling, and segregation. For liquids, flowability relates to viscosity and rheology; in all cases it affects processing performance and equipment design.

Measurement and assessment: Flowability is evaluated with qualitative observations and standardized tests. The angle of repose assesses interparticle friction and cohesion. Flow through an orifice or funnel yields a flow rate; higher rates indicate better flow. Density-based indices such as bulk density, tapped density, Hausner ratio, and Carr index quantify flow potential. Shear-cell tests (Jenike or ISO methods) measure flow under normal stress to reflect conditions inside hoppers and silos. For pastes and suspensions, rheological tests determine yield stress and shear-thinning behavior.

Factors: Flowability depends on particle size distribution and shape, surface texture, moisture, temperature, and electrostatic or cohesive forces. Interparticle and particle-wall friction, caking, aging, and compaction reduce flow, while lubricants or surface coatings can improve it.

Applications: In pharmaceuticals, poor flow can cause variability in tablet weight and dosing. In food processing, consistent powder flow supports mixing and filling. In construction, cement and dry mixes require reliable flow for batching. In additive manufacturing and materials processing, powder flow governs feeding and bed formation.

Standards: ISO, ASTM, and other standards define procedures to measure flowability, including funnel tests, angle of repose, and shear tests, enabling comparison and quality control.