Numerical Simulations of Die Plate Freeze-Off in Underwater Pelletizers

Underwater pelletizers have gained increasing prominence within the plastic compounding industry. These advanced machines are now widely adopted for efficiently processing a wide range of engineering polymers. A typical underwater extrusion pelletizer consists of a solid die with 10–400 polymer holes, the number depending on the required throughput, and a reduction in diameter along the flow direction. The molten extruded polymer is exposed to cold water, where it is cut into pellets according to the required specifications. Additionally, high-temperature oil is used to provide heat to the polymer. One of the potential drawbacks of underwater pelletizers is the possibility of freeze-off. Freeze-off in polymer extrusion refers to a phenomenon that occurs during the extrusion process when a polymer material undergoes a sudden phase transition from a molten state to a solid state. This transition happens due to rapid cooling and results in the obstruction of the polymer holes, causing a blockage. This study investigates the freeze-off phenomenon using a computational fluid dynamics (CFD) model developed in ANSYS FLUENT. Temperature contours are carefully analyzed to assess the likelihood of freeze-off in underwater pelletizers. The current study provides valuable insights for designers and manufacturers, enabling them to implement preventative measures to ensure the consistent production of high-quality polymer pellets in the plastic compounding industry.