Numerical Simulation Of Supercritical Carbon Dioxide And Polypropylene Non-newtonian Gas-liquid Two-phase Flow

In recent years,microcellular foam injection molding technology has achieved a staged development,experienced early plunger injection molding,plunger and screw injection molding,reciprocating screw injection molding,Optifoam microcellular foam injection molding technology,The development of Ergocell microcellular foam injection molding technology and the latest ProFoam microcellular foam injection molding technology in several stages.The main technical difference lies in the difference of supercritical fluid injection and metering methods.In the process of microcellular foam injection molding,super When the critical fluid is mixed and dissolved in the polymer melt,the first step of micro-hole injection molding is successful,and it is also a crucial step in the molding process.Making a good gas-polymer mixture is the face of industrial plasticizing equipment.The real challenge is that after the homogeneous solution is prepared,cell nucleation,cell growth and in-mold molding can be performed to obtain injection parts with stable cell quality.In the plasticizing device,the screw must mix the gas and the melt uniformly.The gas is then quickly diffused into the melt,and a homogeneous solution is prepared before the gas and melt mixture accumulates in the screw head.To obtain an excellent and stable cell structure,the preparation of a homogeneous solution is particularly important.Therefore,higher requirements are placed on the screw structure.This paper proposes a torsion mixing element that can be used as the mixing section of the screw.The torsion element can ensure the up and down movement of the material in the mixing element so that the material can be replaced from the upper layer to the bottom layer,which can promote the supercritical fluid to be more uniformly dissolved in the polymer solution.The thesis takes the torsional mixing element as the research object,analyzes the internal flow field of supercritical carbon dioxide and PP gas-liquid two-phase mixed flow through the CFD numerical simulation method,comprehensively considers the flow characteristics of the.non-Newtonian gas-liquid two-phase flow,and selects the appropriate turbulence model(SST model)and two-phase flow model(Euler model),and the corresponding UDF functions were compiled for the density and viscosity characteristics of carbon dioxide.Observe the distribution clouds of axial velocity,pressure,temperature and gas volume fraction at different cross sections,analyze the uniform mixing effect of the torsional mixing element on the gas-liquid two-phase,and analyze the internal flow field of the torsional mixing element with different speeds and inlet gas content Effect of bubble size distribution.Finally,two designs of the microcellular foam injection molding and plasticizing device are proposed.The first one is to modify the screw structure of the traditional screw,and a new type of microcellular foam injection molding new screw and barrel are designed and developed.The second is the introduction of a melt pump and a static mixer in the plasticizer section of the original injection machine,both of which can promote the mixing of gas and polymer.