Cohesion-driven recirculation of a polymer solids bed in a screw simulator

This paper demonstrates a previously unnoted heat transfer mechanism for solids-conveying in an extruder which certain polymers exhibit. It was found in this study that polyethylenes readily demonstrate bed circulation in a geometry representative of a lid-driven cavity. This granular advective term for heat transfer in the heated chamber resulted in a more rapid rise in overall bed temperature compared to plug-like conditions. The mechanism for this circulation appeared to be a cohesion-dominated phenomenon which requires adhesive forces at the rotating surface to exceed the internal cohesive strength of the solids bed. Conversely, other materials like polypropylene and polystyrene did not readily show this behavior except under more extreme conditions.