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in Wiley InterScience (www.interscience.wiley.com). The effects of particle size and/or density on particle interaction and overall behavior of granular flow were studied using the kinetic theory approach. The kinetic theory for granular flow was extended to mixtures of multitype particles assuming a non-Maxwellian velocity distribution and energy non-equipartition. Each type of particles was considered as a separate phase with different velocity and granular temperature. The resulting momentum equation for each particulate phase includes phase interaction arising from collisional pressure and particle-particle drag force. When applied to simple shear granular flow of a binary mixture, this model predicts well the energy non-equipartition and the stresses of particulate systems with different sizes and densities. © 2005 AmericanInstitute of Chemical Engineers AIChE J, 51: 1620 -1632, 2005 Keywords: kinetic theory, particle collision, granular mixture, granular shear flow, energy non-equipartition IntroductionGranular flows exhibit complex behavior arising from the coexistence of two different behaviors within the flow: solid-like and fluid-like behaviors. Collisions of particles of different mechanical properties and corresponding fluctuations that occur during flow make the system more complicated. In this work, we investigate the effect of particle mechanical properties (size, particle density) on granular flow behavior using the kinetic theory approach.Originally the kinetic theory was developed by Chapman and Cowling 1 for gases to predict the behavior of mass point molecules whose interaction energies are conserved. Nearly two decades ago, this theory was extended to particulate flow where the interactions between particles are not conserved. Savage and Jeffrey 2 were probably the first to apply the kinetic theory to rapidly deforming material in the form of smooth hard spherical particles (ideal mixture). In their derivation, to calculate the stress tensor arising from interparticle collisions, they assumed that the collisions between particles were purely elastic. Although in some granular flows the restitution coefficient is restrained to values close to unity, its deviation from unity results in a significant variation in the properties of granular flow. This was shown first by Jenkins and Savage. 3 They extended the kinetic theory of an idealized granular mixture to predict the rapid deformation of granular material by including energy dissipation during collision for nearly inelastic particles. Later on, based on the original work of Savage and Jeffrey 2 and Jenkins and Savage, 3 Lun et al. 4 developed a theory that predicts the simple shear flow behavior for a wide range of restitution coefficients. Many models for granular flow were then developed based on the kinetic theory approach. [5][6][7] All the above-cited works assumed mixtures of identical density and size. However, real systems are composed of particles of different properties, in which segregation by size or density may occur during t...

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