The rhomboidal mixing section is becoming very popular among processors to provide distributive mixing. Currently, several different designs are used but the details of the flow behavior and mixing efficiency is not well understood. This information is needed to be able to design and find the most efficient rhomboid geometry. In this investigation nine different geometries with various pitches (helix of rhomboids) were analyzed using a 3-dimensional boundary element method (BEM). The geometries were compared according to mixing efficiency, pressure and energy consumption. The results were compared to experiments performed with a conventional single screw extruder that was fitted with three different rhomboidal mixing sections. The investigation led to the conclusion that the most effective distributive mixing sections were those with neutral rhomboids (pineapple mixer). However, the neutral rhomboidal mixing section consumes the most pressure in the extruder. It was also concluded that rhomboidal mixing sections deform the material by shear, making them poor dispersive mixing sections.

Mixing has been the focal point of many experimental studies in recent years, but advances in modeling and simulation now allow for fast, accurate and useful simulation analysis. Numerous mixing indices have been developed but the majority are tailored to experimental studies. In this study, a new mixing index is developed to analyze the particle position history of the mixer. Due to its simplicity when dealing with moving boundary problems, the boundary element method is employed to model the fluid flow and track particles.Numerous geometries can be modeled and compared on a basic workstation. First the mixing index is applied to Couette flow. Analytical and boundary element simulation results compare well. Next the method is used to analyze the mixing capabilities of a Banbury mixer with different speed ratios. Further the mixing index is used to compare the mixing capabilities of triangular mixing lobes versus typical Banbury type.

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A pseudo‐analytical model for the forces exerted on fibers during flow that lead to fiber damage is proposed and solved. The fundamental derivations for the forces on fibers moving in suspensions developed by Burgers (1938) were used as a comparison. The cases of the motion of a fiber along its axis and perpendicular to its axis and in shear flow at a −45 degree‐angle were investigated for aspect ratios between 10 and 300. The values for the overall forces on the fiber were in good agreement with the results found earlier by Burgers and others. However, the force distribution along the fiber was found to be significantly different from the constant distribution assumed by Burgers. Because of the higher forces on the fiber from the exact solution, the criterion for the onset of buckling in shear flow was revised. The pseudo‐analytical solution was also compared to numerical results done with the boundary element method (BEM); the results were in good agreement.