Self-stretching Of Melt Based On Field Synergistic Heat Transfer Theory Screw Structure Optimization Study

With the energy crisis and environmental problems becoming increasingly serious,many countries have made achieving carbon peaking and carbon neutrality an important goal of their national strategies.Therefore,in the chemical industry,the development of efficient low carbon technologies has become one of the most pressing issues at present.For polymer processing,extruders are usually used for melt plasticization,and mechanical energy is converted into internal energy of the melt by changing the screw speed,but the energy conversion efficiency and plasticization quality are low.For this reason,it is of great importance to improve the efficiency and quality of polymer melt plasticization to achieve a low carbon and low energy consumption production process.The way of mass and heat transfer in polymer plasticization process directly affects the plasticization uniformity of the products,and uneven plasticization is the key reason for the quality defects of the products.The special nature of polymer rubber,poor thermal conductivity,viscoelasticity,and the existence of dynamic heat generation and loss phenomenon,in the plasticization process has a large flow resistance,it is difficult to dissipate heat,uneven heat distribution caused by shear heat generation,heat aggregation of rubber products caused serious damage,resulting in scorching,flow marks,lack of rubber,comprehensive mechanical properties decline and other problems.As the most critical component in the plasticizing process,the structure of the screw is crucial to the plasticizing efficiency and quality.In order to solve and improve the outstanding thermal problems of polymer rubber in the extrusion and plasticization process,this topic is based on the principle of polymer multi-field synergistic enhanced heat transfer and efficient mixing of melt self-stretching screw(hereinafter referred to as stretching element),numerical simulation analysis around the structure and arrangement of stretching element,and from the perspective of screw extrusion process regulation,based on the polymer multi-field synergistic enhanced heat transfer and efficient mixing The new idea,through specific flow field design,aims to improve the coupling synergy between flow and thermal flow fields,thus improving the radial convective heat and mass transfer in the screw plasticizing system,providing effective control of fluid internal thermal management and temperature uniformity,and improving plasticizing efficiency and quality.The main research works in this paper are as follows:(1)The analysis of the melt self-extending screw structure reveals the ability of the melt-extending screw to enhance mass and heat transfer.The stretching deformation caused by the wedge-shaped converging channel of the melt stretching screw makes the angle between the velocity vector and the temperature gradient vector no longer perpendicular,which enhances the synergistic effect of the flow and temperature fields and promotes the radial mass and heat transfer,thus improving the melt efficiency and plasticization quality.In addition,the diverging converging structure of the melt selfextending screw increases the fluid particle disturbance and makes the motion more random,which in turn strengthens the mixing and mass transfer of the whole system.(2)The study of the inclination angle of the split prism of the melt stretching screw shows that it has an effect on the conveying performance,mixing performance,heat transfer performance and plasticization uniformity.With the increase of inclination angle,the positive displacement conveying ability of the screw is enhanced.Compared with the common threaded screw,the melt self-extending screw creates radial flow while maintaining axial flow,which greatly improves the mass and heat transfer ability,has a better temperature distribution and viscosity distribution,and the plasticizing ability of the melt-extending screw is further improved.(3)Based on the optimized design of melt stretching screw inclination angle in the previous chapter,the influence law of melt stretching screw arrangement on conveying performance,mixing performance,heat transfer performance and plasticization uniformity was explored and analyzed.The study shows that the embedding of the melt self-extending screw reduces the overall differential pressure of the screw,and the conveying capacity of the screw tends to decrease as the dispersion of the elements increases;the arrangement of the melt self-extending screw has a great influence on the mixing of the rubber,and the higher the dispersion,the better the mixing effect;although the increase in the dispersion of the stretching elements has a slight decrease in the heat transfer performance of the screw,after normalizing the convective heat transfer coefficient,but heat transfer performance is still better than the ordinary screw.(4)The effect of the introduction of the barrel pin structure on the flow field performance of the melt self-extending screw was investigated by combining the structural characteristics of the cold-fed pin extruder.The addition of pins negatively affects the transport capacity of the screw and reduces the glue flow rate.The reduction of the velocity field itself in the field synergy principle reduces the heat transfer strength of the glue and affects the heat transfer performance of the screw.However,the mixing ability of the screw is further improved by characterizing the mixing performance such as the mixing efficiency of the rubber and the first eigenvalue of the inelastic stress tensor.In addition,the pin improves the tensile rheological properties within the rubber,and the plasticization uniformity of the melt from the tensile element is further improved,but at the pin position,the temperature difference of the rubber is larger,and the viscosity distribution is uneven near the barrel wall position,and the local plasticization effect is poor.