2. Physical principles associated with flow

Appropriate silo sizing for bulk flow depends on silo geometry and powder flow properties. In particular, the flow is conditioned by the ratio between two antagonistic forces which result respectively :

• the stress field generated by the weight of the product, which tends to consolidate the medium;

• mechanical properties of the solid.

  Despite many similarities with liquids, the flow of powders is not governed by the same physical principles or phenomenological laws. For a liquid, viscosity is a perfect indicator of its flow, whereas for a solid, even in a dispersed state, the notion of viscosity loses all meaning. As with massive solids, for a consolidated powder, flow occurs if one part of the powder can slide relative to another. Thus, powder flow is associated with its resistance...