Flow Characteristics And Heat Transfer Enhancement Mechanism Of Field Synergy Screw In Polymer Plasticizing Process

Forced convection and enhanced heat transfer in polymer plasticization process have an important effcet on the melting and plasticization of polymer,and the plasticization uniformity of polymer will directly affect the quality of final products.Inhomogeneous plasticization of materials is easy to cause defects in precision products.Therefore,effective heat management and effective control of temperature in polymer plasticization process are of great practical significance.In this paper,the development of polymer plasticization theory and field synergy principle was summarized,and the flow and heat transfer mechanism of polymer plasticization process was carried out.The entropic effect in polymer mixing process and the synergistic effect in heat transfer process of polymer were further proposed,which have been elaborated and demonstrated in detail.Based on the new multi-field synergy theory of heat transfer enhancement,a novel torsion element is innovatively designed to induce torsional flow.The mixing and heat transfer mechanism of polymer in torsional flow was explored by numerical analysis,cold visualization test and hot multi-parameter on-line monitoring test.This new method solves the problem of non-uniform plasticization,provides theoretical guidance for the development and application of high performance materials,and expands the knowledge of field synergy theory in the field of high viscous non-Newtonian fluids.The main work in this paper is divided into five parts.(1)Multi-field synergistic method of heat and mass transfer enhancement in polymersThe entropic effect and synergistic effect in polymer plasticization process were innovatively proposed.It is demonstrated that the random development of particles is the essential factor causing mixing,including displacement randomization and particle size randomization,and the synergistic coupling relationships among the physical fields,such as velocity shear rate,velocity gradient and temperature gradient fields,were studied.The feasibility of the synergy theory in polymer processing is also verified and it provides a new theoretical basis to guide structural design of the screw.A novel torsion element and field synergy screw for heat transfer enhancement and high efficiency mixing were innovatively designed.The mixing model,heat transfer model and melting model of torsion element were analyzed.The torsion element increases the mass entropy and field synergy of particles,i.e.,it improves the degree of disturbance and randomization of fluid,and the synergy between velocity and temperature gradient fields.It has the function of diversion,confluence and torsion,which is benificial to the mixing,heat transfer and temperature uniformity of polymer fluid.2)Enhanced mass transfer characteristics of polymer in torsion element and field synergy screwThe introduction of torsion element makes the polymer obtain local helical flow in the channel,strengthens the radial mass transfer of the fluid,and improves the mixing and plasticizing properties of the polymer melt,which makes the physical parameters such as temperature and viscosity distribution of the polymer melt more uniform,thus ensuring the product quality.Compared with a conventional screw,the synergy screw has good mixing performance,especially when the torsion elements are decentralized arranged in the screw with one pitch apart.(3)Enhanced heat transfer mechanism of polymer in torsion element and field synergy screwThe introduction of torsion element improves the synergy between velocity and temperature gradient fields to achieve good convective heat transfer performance.The heat transfer in the extrusion system improves with the increase in torsion element numbers and dispersed arrangement,which have an effect on the melting and heat transfer characteristics of polymers.In addition,field synergy screw achieves better heat transfer performance than conventional screw without additional energy consumption.The field synergy theory can well explain the heat transfer performance of non-Newtonian viscoelastic fluids in polymer plasticization process,which can be used to guide the design of screw structures.It provides an effective method to improve the plasticizing ability and heat transfer enhancement,and opens up a new way to solve the problem of poor plasticization in screw plasticization system.(4)Establishment of comprehensive evaluation system for plasticization screw performanceA comprehensive evaluation system of screw performance in polymer plasticizing process was established.The screw performance was quantitatively analyzed from five aspects:mixing,heat transfer,plasticization,energy consumption and synergy.The mixing evaluation factor,heat transfer evaluation factor,plasticization evaluation factor,energy consumption evaluation factor and synergy evaluation factor were determined.Multi-objective decision-making and comprehensive evaluation of screw performance have offered a new way to quantitatively evaluate the influence of screw performance.(5)Application of field synergy screw in polymer microcellular foaming and fiber reinforced compositesWith the self-designed field synergy screw,a chemical foam with cell size of less than 100 ?m,physical foam with cell size of less than 10 ?m,and a recycled carbon fiber reinforced polypropylene composite with average fiber length of 500 ?m or more were successfully prepared.In summary,aiming at the problems of temperature control and heat management in polymer plasticizing process,a new method of polymer multi-field synergy for heat transfer enhancement and high efficiency mixing are proposed,which can be used as a reference for the optimization design of polymer screw plasticization system and solve the problem of inhomogeneous plasticization of polymer melt.