4. Flow models

As we've just seen, the co-mixer is a complex tool, and it's easy to see why flow modeling could be an interesting tool for better understanding and optimizing the operation of these machines. However, the problem is much more difficult than for other extrusion processes (single-screw, twin-screw or counter-rotating), due to the particularities already mentioned: oscillating screw motion, prohibiting a stationary approach, presence of thread interruptions, trajectory of the mixing fingers, etc. In what follows, we present the various approaches taken from the literature, highlighting the current limitations of these models.