(150e) Caking: Predicting the Bulk Strength of Granular Materials

Caking is the process by which free flowing material is transformed into lumps or agglomerates due to changes in atmospheric conditions. This phenomenon can be seen in bulk materials such as food powders, detergents, pharmaceutical feedstocks, fertilizers, and inorganic salts which often gain strength during storage. A caking event develops from the presence of moisture in the environment or the particle. However, factors such as the storage time, consolidation pressure, particle size, initial moisture content and the number of temperature cycles determine the magnitude of the cake strength. These influential factors along with a proper caking mechanism must be accounted for when evaluating the strength. Many of the current models are based on the theory of Rumpf which states that the strength is inversely proportional to the squared particle diameter. This dependence on particle diameter does not properly fit the measured data. Therefore, a new model is proposed based on the principles of fracture mechanics. The strength is predicted as a function of consolidation pressure, moisture content and particle size.