3-D numerical analysis on the mixing performance for assemblies with filled zone of right-handed and left-handed double-flighted screws and kneading blocks in twin-screw extruders

We have calculated and visualized numerically the mixing performances of four kinds of assemblies in twin-screw extruders that were composed of right-handed or left-handed double-flighted full fight screws and neutral or left-handed stagger angle kneading blocks, taking into consideration industrial usage. We have found that the mixing performance of a kneading block interposed between full flighted screws is strongly influenced by the flow of full flighted screws, in particular that of a neutral kneading block. Furthermore, we have proposed the simple mixing indices, which could describe both uniform mixing and heterogeneous mixing, and also applied them to our marker tracking results of four kinds of assemblies. We found that more uniform mixing is obtained for the assembly that has a neutral kneading block before the right-handed full flight screw, and a more enhanced heterogeneous mixing is obtained for the assembly that has a left-handed kneading block before the left-handed full flight screw. The reason for the latter mixing ability will relate to the quasi-channels of the left-handed kneading block, through which marker clusters flow while elongating.