Numerical comparison on the influence of geometric size on melt viscosity for conventional and gas-assisted extrusion of plastic micro-tube

We studied the effects of the geometric size on the viscosity of melt for plastic micro-tubes with different radius or L/D ratios by using the finite element method in this paper. Meanwhile, the Bird-Carreau constitutive model was used to describe the rheological properties of non-Newtonian melt. Two of geometric models were used in this study. For the geometric model with same L/D ratio but different radius, the same inlet pressure value was imposed on the inlet face of geometric model. For the geometric model with the same radius but different L/D ratios, the same inlet volume flow rate of melt were imposed on the inlet face of geometric model. Numerical results show that, for the conventional extrusion of plastic micro-tubes with same L/D ratio but different radius, the apparent viscosity of melt decreases with the decreasing of the radius. For the plastic micro-tubes with same radius but different L/D ratios, the apparent viscosity of melt is nearly not changed with the decreasing of the L/D ratio. However, for the gas-assisted extrusion of plastic micro-tube, the geometric size doesn't seem to affect the melt viscosity. (paper)