Study On Mixing Mechanism Of New Type Eccentric Twin Screw Extruder

Meshing co-directional twin screw extruder has the advantages of good mixing effect,strong self-cleaning performance,high output,low energy consumption,and is widely used in the processing of polymer materials,paper and other industries.The co-directional twin screw extruder is composed of different screw function segments.With the development of polymer materials,more stringent requirements are put forward for the mixing extruder.The traditional dispersing and distributing mixing has low mixing efficiency and high energy consumption,so it is not suitable for the processing of some special materials.It is easy to damage its structure and performance and affect the extrusion yield and quality.On the basis of this problem,researchers put forward chaos mixing theory,chaos mixing as one of the main forms of high viscosity fluid mixing,people gradually pay attention to.Chaotic mixing has the advantages of soft shear and high mixing efficiency.Eccentric stirring is one of the ways to induce chaotic mixing.In the field of polymer materials,there are still many gaps in the mixing mechanism and mixing characteristics of eccentric stirring.The purpose of this paper is to compare the mixing characteristics and mixing efficiency of eccentric mixing elements(eccentric meshing disc elements),eccentric conveying elements(eccentric thread elements)and their screw combinations with that of traditional screw elements,so as to provide a more intuitive demonstration for understanding eccentric stirring.Firstly,the overall and local pressure and velocity vector fields of eccentric screw elements and conventional screw elements are analyzed,the flow rules of eccentric stirring are obtained,and the differences of flow characteristics between eccentric screw elements and traditional screw elements arecompared.Then,the overall and local shear velocity fields and mixing exponential fields of eccentric screw elements and conventional screw elements were analyzed,and the global characteristics of eccentric stirring flow mixing were further understood.Next,the logarithmic tensile rate,cumulative maximum shear rate,residence time distribution,distribution index and separation scale of eccentric screw elements and traditional screw elements are compared.Through the above comparison,the advantages and disadvantages of eccentric mixing over traditional screw mixing efficiency are fully understood.At the same time,the mixing efficiency of eccentric screw elements under different geometric parameters was compared,which revealed the influence of geometric parameters of the rotor on mixing in the flow field,especially the influence and effect of eccentricity on dispersion and distribution mixing.Finally,the particle trajectory and mixing characteristic curve reveal the mixing characterization of eccentric stirring from the micro level.In order to make the material according to the process requirements to complete the whole melting mixing extrusion process,this requires the corresponding screw configuration to achieve the purpose.Through the reasonable combination of the screw,the mixed energy of the whole screw can be improved.Finally,the combination law of meshing disc and thread element is studied and analyzed to improve the mixing performance of extruder.The relationship between geometric parameters and mixing performance of different meshing disc and thread combinations is studied and the design rules of different eccentric screw combinations are obtained.