| Many industries such as food service, pharmaceutical, chemical, and agricultural handle and store materials in granular form. The processing of granular materials can pose many challenges. The materials can gain strength during storage creating flow problems in process equipment. This phenomenon is known as caking and is defined as the process by which free flowing material is transformed into lumps or agglomerates due to changes in environmental conditions. The strength of a cake is a function of various material properties and processing parameters such as temperature, relative humidity, particle size, moisture content, and consolidation stress. A fundamental understanding of the entire caking process is needed in order to predict a caking problem.;In this research, caking based on the mechanism of moisture migration through the particle bed is studied. The influence of moisture content, consolidation stress, particle size, and humidity are investigated. An increase in these variables causes an increase in the unconfined yield strength of the material. Theoretical models exist to describe the function of particle size and moisture content on the yield strength. However, the consolidation stress is not included in these models. The trend is often qualitatively explained by an increase in the interparticle forces. Applying this theory to the current research yields an incorrect prediction of the unconfined yield strength. It is postulated that the increase in unconfined yield strength is attributed to an increase in the number of major force chains in the shear zone. An increase in the number of major force chains results in the increase of the yield strength of the material. Using the principles of fracture mechanics, a new equation is developed to evaluate the strength of powder cakes. An improvement of existing cake yield strength models is made by including the consolidation stress.;Moisture migration through the particle system and moisture uptake by the particles themselves are significant factors of caking. These processes are modeled using a finite element partial differential equation solver, COMSOL Multiphysics. The heat and mass transport of the system is described as well as the kinetics of the material. The model is used to predict the areas of caking within a given geometry and approximate the unconfined yield strength. |
