Distributive mixing in conveying elements of a ZSK-53 co-rotating twin screw extruder

A fluid dynamics analysis package (FIDAP), using the finite element method, was implemented to simulate the 3-D isothermal flow patterns in the conveying element of a ZSK-53 co-rotating twin screw extruder. The fluid was described by a power-law model. The dynamics of distributive mixing was studied numerically by tracking the motion of particles in the mixer. The extent of distributive mixing was characterized in terms of length and area stretch as well as strain distributions. The length stretch reflects the overall capability of the mixing device to spread minor component particles away from their neighbors originally present in the same cluster. The area stretch reflects the evolution of intermaterial area when mixing two fluids with a passive interface. We observed an oscillatory behavior for the average intermaterial area stretch, which was explained in terms of a stretching and folding mechanism. Folding occurs during material takeover from one screw to the other. Operating at higher rotational speeds enhances distributive mixing efficiency.