Investigation of Granular Segregation in a Horizontal Rotating Tube from an Energy Perspective

Granular segregation is a common phenomenon that occurs when binary (two grain sizes) granular materials are subjected to vibration or mixing agitation. Practical examples occur in materials handling applications from pharmaceuticals to construction and the result is usually undesirable. Although much research exists on this phenomenon, previous predictive models appear to be based on visual observations. The authors have found no models that establish a cause and effect relationship. Recent (summer 2007) research reveals that an energy-related phenomenon is occurring during granular segregation. Experiments were conducted using black beans and rice as the granular material in a horizontal rotating tube. Decreased rotational torque required to turn the tube is consistently detected and correlates well with visual observations of the progression of segregation. Copious amounts of literature exist regarding the segregation phenomenon. Literature on the physics of fluids and gases seem to have more energy related theories regarding segregation of binary granular mixtures. However, none have either predicted or observed a decrease in rotational torque. Our observations provide new parameters with which to model the segregation phenomenon and may lead to a better understanding of the physics involved.