A Method for the Validation of Simulated Mixing Characteristics of Two Dynamic Mixers in Single-Screw Extrusion

Abstract

The field of simulation and optimisation of dynamic mixing elements (‘mixers’) is lacking good methods for spatially resolved validation and flow visualisation. For this reason, the authors present an experimental setup that gives better insight into the thermal, distributive and dispersive mixing process by measuring melt temperatures upstream of the mixer and injecting a secondary, visually distinguishable stream of melt upstream. Running extrusion trials for a polyethylene on both a rhomboidal and a Maddock mixer, temperatures, gray scale distribution of images of extrudates and size of dispersed domains in incompatible polystyrene were measured. It was found that temperatures upstream and downstream of the mixer can be quantified. This was used to validate a simulation of thermal mixing. In distributive mixing, good agreement with simulation and an excellent spatial resolution were observed, thereby identifying an area of the rhomboidal mixer in need of geometric improvement. For dispersive mixing, a trend coherent with extrusion theory was found.

Impact of Intensive Mixing and Shearing Elements on the Effectiveness of Extrusion of Wood Polypropylene Composites

“…It results from the fact that the volume of the flow channels in the Maddock mixer is lower and thus the melt flow resistance of this mixer is higher than that of the cut ring mixer in which the flow channel volume is higher and thus the melt flow is more efficient. In addition, it should be stressed that in the Maddock mixer the flow is predominantly radial, while in the pineapple mixer it is axial flow that is dominant [19]. For the tested filler contents, the highest increase in mass flow rate can be observed when the cut ring mixer is used.…”

“…The highest increase in the temperature of the polypropylene sample containing 10-20 wt% of the natural filler and extruded with the use of the Maddock mixer may result from the fact that the melt flow is predominantly rotational here, while the other key direction of material flow is that along the axis of the mixer. The combination of these two flows probably causes the melt to pass at least once through the inlet and outlet grooves and barrier flight [19]. The occurrence of the two types of flow probably results in intensive generation of friction heat.…”

“…The highest flow rate can be observed in the vicinity of the rhomboidal diamond. Also, the flow rate is high in the gap between the rhomboidal diamond and the barrel [19], which can be explained by a slight increase in the screw rotation speed.…”

Effect of Surface Nanopatterning on Slip: The Case of Couette Flow of Long-Chain Polyethylene Melt Flowing Past Gold Surfaces

“…Numerical simulations of rheological models have aided immensely the design of efficient applications in the aerospace industry, fluid mixing, tribology, , nuclear reactors, blood rheology, surfaces with antimicrobial properties, and microfluidic devices . A wide class of such simulation methods involves the solution of approximant forms of the Navier–Stokes equations.…”

“…Another way to think about this is the following: In a frame of reference moving with the plate, the polymer would tend to flow backward along the grooves. The component of this slant backward velocity normal to the direction of motion of the plates gives rise to the "sweeping" effect described in action (2).…”