Numerical study on mixing performance of screw elements in intermeshing counter-rotating and co-rotating twin-screw extrudes

The flow process of unplasticized polyvinyl chloride(U-PVC)through the mixing zone of intermeshing counter-rotating and co-rotating twin-screw extruders(TSEs)were numerically simulated by the finite element method.Three-dimensional isothermal flow field of U-PVC in two kinds of TSE was calculated.The mixing performance of the screw elements of the extruders was statistically analyzed by particle tracking method.The dispersive mixing performance was characterized by the mixing index,the logarithm of stretching,and the segregation scale.The distributive mixing performance was characterized by the resident time distribution.The results indicate that the counter-rotating TSE can build higher pressure and generate higher axial velocity and shear rate,whereas the co-rotating TSE has better performance in dispersive and distributive mixing.