Numerical Characterization of Mixing in a Kneading Element Channel of Dual-Speed Corotating Non-Twin Screws Using Lagrangian Statistics Method

A novel kind of dual-speed corotating non-twin kneading elements with a zero stagger angle is designed to improve mixing ability. The physical model considering several narrow gaps is developed where the inlet and outlet transition sections are also included. Finite element method associated with the mesh superposition technique is further applied to solve the time-dependent flow field where fluid is assumed to obey the Carreau constitutive model. The tracers initially from different locations are tracked using a self-developed fourth-order Runge–Kutta scheme. Distributive mixing is evaluated through evolution of tracer droplets and decaying of variance index with time. In addition, a Lagrangian statistics method is used to characterize the dispersive mixing in terms of the statistical distributions of mixing index and their integration areas within the range of mixing index larger than 0.5. In contrast, the kneading elements of a conventional twin screw configuration are also modeled to show the mixing difference.