Scale‐up of counter‐rotating closely intermeshing twin screw extruders without and with reactions

Abstract Many scale‐up rules and theories have been presented in the area of extrusion. Until now all the theories concerned the single screw extruder. As the use of counter‐rotating twin screw extruders is increasing, it becomes important to propose scale‐up rules for this kind of extruder. Therefore a basic analysis of scale‐up in a twin screw extruder has been developed. It can be concluded that important factors scaling up a twin screw extruder are the fully filled length and the leakage flows of the extruder. So hydrodynamic similarity has to be assured in the scale‐up of most processes. However no serious constraints are put on the throughput of the extruder by this consideration. When the extruder is scaled up on the basis of thermal similarity the Brinkmann number is of importance. At low Brinkmann numbers the throughput is unfavorably affected by scale‐up. If the Brinkmann number is high the throughput is proportional to the diameter cubed. If the extruder is used as a chemical reactor for polymerization, an increasing area of research, the scale‐up rules are dependent on the Damköhler IV number. For low Damköhler IV numbers no consistent scale rules are found. However if the Damköhler IV number is high, useful rules for the scale‐up can be derived.