Numerical Simulation and Analysis of CO2 Bubble Deformation in PET Continuous Extrusion Process

Abstract

In this paper, the dynamic deformation of supercritical CO₂ bubbles in the shear flow field of polyethylene terephthalate (PET) is analyzed, and the dynamic continuous extrusion process of PET microcellular foaming is numerically simulated. The extrusion process of PET supercritical CO₂ homogeneous solution is simulated by the user defined function (UDF) program, and the volume of fluid (VOF) method is used to track the gas-liquid interface. The deformation of supercritical CO₂ bubbles in the PET microcellular foaming extrusion process is simulated in FLUENT software. It is found that in the continuous dynamic extrusion process, the bubble moves with the polymer at a certain angle, and there will be an area at the two ends to inhibit the shear thinning of the melt, which affects the movement pattern of the bubble. The increase in shear rate is the main factor causing the increase in the aspect ratio of the bubble. The increase of the rheological index can promote the bubble to maintain the spherical shape by affecting the shear flow field around the bubble. In addition, it is found that the effect of surface tension on bubble morphology in the shear flow field is not as large as that in the static flow field.