The Flow of Granular Materials

The handling of granular materials is of  great importance in many industries.  For example, in the chemical industry,  it is estimated that roughly one-half of the products and three-quarters of the raw materials are in the form of granular materials.  When one adds wheat, sugar, iron ore, cement, or sand and gravel, and the fact that these need to be transported and stored, the importance of granular materials becomes self-evident.

When contained, granular materials are usually stored in hoppers or bins.  They can vary in size from a salt shaker which contains hundreds of grams to larger vessels containing thousands or even tens of thousands of tons.  For example, agricultural hoppers, that contain, for example, grain or corn, can measure up to 20m in diameter and 60m in height.  The ability to predicate stress distributions and flow properties throughout the hopper becomes extremely important.  In fact, the stresses can become so large that hoppers have been known to literally collapse (see Fig. 1).  In addition, the flow patterns can be so complex (see fig. 2) that even today there is no one single theory that is generally accepted by everyone.  Thus, the study of granular materials continues to be topic of much current research.

Fig. 2.  Funnel Flow