Granular materials may readily segregate due to differences in particle properties such as size, shape, and density. This segregation may occur in many industrial processes involving transport or other handling of granular materials and will occur even after a material has been uniformly blended. The discharge of granular material from a hopper is a typical example of such a process that may cause segregation. The present work investigates the causes and extent of segregation of cohesive granular materials during flow from a hopper. In the system considered, the most important source of cohesion is pendular liquid bridges existing between particles. The liquid bridge force is strongly dependent on the geometry of the liquid bridge and is a result of surface tension and the pressure differential created in the liquid.

The cohesive granular material is modeled as bi-disperse inelastic, frictional spheres via the discrete element method (DEM). Regression expressions are implemented into the DEM code to describe the liquid bridge force as an explicit function of separation distance between the particles, contact angle, surface tension and liquid volume. Segregation and discharge rate data are obtained from the discharge of quasi-three-dimensional wedge-shaped hoppers. The extent of the discharge segregation over time is determined as a function of the hopper parameters and particle properties. In addition, simulations for a monodispersed cohesive granular system show an increase in residence time and significant differences in the shape of the hopper free surface when compared to the cohesionless granular system. For the cohesive granular system, sticking of particles to the hopper wall and clumping of particles as they flow out of the hopper are observed.