Numerical Simulation of Mixing Enhancement in a Single Screw Extruder by Different Internal Baffles

Abstract

The metering section of an industrial-scale single screw extruder is modeled, and two kinds of discontinuous baffles, three rows of plate baffles, and two types of plow-shaped baffles, arranged in staggered or parallel ways, are proposed to improve the distributive and dispersive mixing. Considering the narrow gap between the screw and barrel, the finite element method along with the mesh superposition technique is applied to solve fully 3D isothermal flow fields where the fluid is assumed to obey the Carreau constitutive model. The computation codes are successfully developed to achieve particle tracking using the fourth-order Runge–Kutta scheme. Distributive mixing is evaluated in terms of the evolution of tracer particles and Poincaré sections. Dispersive mixing is then examined in terms of shear rates, mixing index, distribution probability function of mixing index, and its integral function for particles tracking with time. For the same pressure drop and the same screw rotating speed, when compared to the conventional single screw, the numerical simulation results showed that the screw with staggered plow-shaped baffles achieved better distributive mixing with the output nearly unchanged while three rows of plate baffles significantly enhanced both distributive and dispersive mixing at the cost of output reduction by 13.2%.