Hydrodynamics and mixing process in a horizontal self-cleaning opposite-rotating twin-shaft kneader

Abstract

The finite element method (FEM) simulation was adopted to investigate the hydrodynamics in an opposite-rotating horizontal self-cleaning twin-shaft kneader with a highly viscous Newtonian fluid. The complicated motion of impellers was simulated by using the mesh superposition technique (MST). The particle tracking technique was used to evaluate the mixing process. The stretching rate from the trajectories of particles was quantitatively characterized to calculate the mixing efficiency. A small visual experimental apparatus was also designed to study the mixing process. The mixing processes by visual experiment show good agreement with the FEM simulation data. The velocity and shear rate are larger in the faster rotation speed side since the rotation speeds of these two shafts differs. The kneading bars on the left and right shaft only intermesh in the center of the overlapping zone. There exists the material exchange between the left and right chamber due to periodical intermeshing interaction. The intermeshing kneading bars split the center-initial cluster into two parts and push them into the left and right region of the lower part of the kneader, respectively. The mean length of stretch increases exponentially with time. The mean value of the mixing efficiency remains positive at all times.