Mass flow during unloading of agricultural bulk materials from silos depending on particle form, flow properties and geometry of the discharge opening

•Flow properties influenced by the fraction of cohesive fines and particle shape.•Flowability decreases as the cohesive fines and the form factor increase.•Accordingly, the discharge opening must be enlarged for undisturbed flow.•Froude number and discharge mass flow rate are affected by flow properties, as well.•Close, almost linear relation between Froude number and flowability.

Knowledge of the grain and powder mass flow in silos and hoppers during free outflow is important for some tasks in installation planning. It can be expressed by the Froude number as a dimensionless similarity indicator. The objective of the investigations is to record the influence of the flow properties and in particular of the particle form of crushed grain products. In the pertinent literature the particle form is generally stated as less significant by comparison with the particle size. As hardly any results are available for crushed grain products so far, experiments were conducted with two particle size fractions in the range of x = 0.3…0.8 mm that possess slightly cohesive or cohesionless properties. The particle form was characterized by the ratio of particle length to particle width (elongation). It is evident in all results that the deviation from the spherical shape influences the particle properties. In the particle fractions examined, the flowability according to Jenike decreases as the elongation increases. The Froude number determined during the unloading experiments decreases with strong correlation as the elongation values increases, in line with the reduction in flowability of the bulk material samples.

Graphical abstractAs could be demonstrated by unloading experiments from a model silo, there is a close, almost linear connection between the Froude number Fr calculated from the discharge mass flow rate and the flowability ffc of the crushed grain powders independently of the particle form (elongation) and particle size.Figure optionsDownload full-size imageDownload as PowerPoint slide