Comparative analysis of heat and mass transfer processes in the extruder dosing zone with the use of different spatial mathematical models and rheological law
At present, polymer compositions based on polyethylene or PVC are widely used as insulating materials. The processing of these materials is associated with a number of problems in the choice of rational processing modes. In order to minimize the time and cost necessary to determine a particular technological regime, methods of mathematical modeling are used. Development and analysis of various mathematical models of the flow and heat transfer in helical channels allows us to evaluate the possibility of using simplifying assumptions and their effect on flow pattern and process parameters during processing of polymeric materials in extrusion equipment. In this work, a three-dimensional model of flow and heat transfer processes in the dosing zone of a plasticizing extruder taking into account the clearance above the crest of the screw is developed, and the numerical study of a polymer melt flow in this zone is presented. The analysis of spatial mathematical models with different channel geometry (a rectangular channel deployed on plane and a screw channel having much in common with that used in the actual process of recycling) is carried out. The influence of assumptions of the inverted movement of the screw on the polymer melt flow character for the considered spatial models of heat and mass transfer process is evaluated. The effect of the clearance between the crest of the screw and the inner surface of the housing on the temperature distribution in the channel is investigated. Experimental plots of viscosity versus shear rate for the insulating polymer compositions are obtained and the empirical coefficients for the three rheological laws (power law, Kerry model and Crosse model) are determined. A numerical comparison of the calculation results obtained for this rheology models of polymer melt under complex shear in the extruder screw channel is performed. The values of maximum and medium temperature at the outlet of the channel and a comparison with the results obtained by other authors are given.