Numerical analysis of enhanced heat transfer by incorporating torsion elements in the homogenizing section of polymer plasticization with the field synergy principle

The polymer plasticizing process is one of the most important stages in an extruder plasticizing unit. 3D numerical simulations have been carried out in order to investigate the heat transfer and fluid flow characteristics of an extruder plasticizing unit equipped with various screws. The use of screw elements with a twisted groove (namely torsion elements) has been proposed for the first time. The magnitude of radial temperature fluctuations is within 10 K in the position of torsion elements, while it is more than 25 K in other positions. The simulation results reveal that screws with such torsion elements give rise to a more uniform temperature distribution and better heat transfer performance than conventional screws without torsion elements. The mechanism by which the torsion elements enhance the heat transfer was also analyzed using the field synergy principle. The Nusselt number is negatively correlated with the field synergy angle, and the correlation coefficient increases with the screw speed in the range of faster than 60 r/min. The local field synergy angle and heat transfer coefficient have the minimum and maximum respectively at the position where the swirling flow appears. The periodic changes in the flow field induced by the torsion elements are able to improve the synergy between the temperature gradient and the velocity fields, which increases the Nusselt number and the coefficient of local heat transfer, and consequently enhances the overall heat transfer. (C) 2017 Elsevier Ltd. All rights reserved.