5. Results and discussion

polyethylene, and polyurethane.). Therefore, we assume modeling and simulated results based on the above conditions, which are generally applicable for most of the

In our work, ANSYS Polyflow 17.0 packaged software (ANSYS, Inc.) was adopted in the simulations. The 3D mesh systems for the screw and the fluid were created using the mesh superposition technique (MST). Figure 4 shows the 3D model for screw E. The fluid model and screw model were implemented through mesh refinement by hexahedral and tetrahedral elements, respectively. In addition,

Density ρ 735 kg/m<sup>3</sup> Thermal conductivity λ 0.15 W/(mK) Specific heat capacity Cp 2100 J/(kgK) Zero shear viscosity η<sup>0</sup> 26,470 Pas Non-Newtonian index n 0.38 Natural time t 2.15 s Coefficient of temperature sensibility B 0.02 K<sup>1</sup> Reference temperature T0 513 K

Density ρ 8030 kg/m3 Thermal conductivity λ 16.27 W/(mK) Specific heat capacity Cp 502.4 J/(kgK)

Location Flow boundary conditions Thermal boundary conditions

Inlet Setting zero pressure 513 K Outlet Setting zero pressure Heat outlet Barrel wall No-slip wall 513 K Screw wall Screw speeds: 40,60,80,100,120 r/min Free boundary

materials used in polymer processing.

Thermosoftening Plastics

Table 3.

Table 2.

Figure 4.

Table 4.

24

Boundary conditions.

Physical parameters of the screw.

Physical parameters of the PP.

Three-dimensional physical model of screw E.

#### 5.1 Temperature uniformity

Firstly, we investigated the axial melt temperature distribution by selecting different radial reference lines for these six screws as shown in Figure 5. From all the six screws, we can find that the temperature fluctuations decrease by the effect of torsion elements and the temperature difference between melt and barrel wall in the position of torsion elements is smaller than that of the position of screw elements. The reason for this phenomenon is heat transfer enhancement caused by the synergy effect between velocity and temperature gradient. We will prove this in the next section. Figure 6 shows the radial melt temperature distribution for screw B in the position of torsion and screw elements. For the position of torsion element, almost all the fluid is in a high-temperature region, more than 500°C, while the radial temperature for most fluid in the screw channels is below 500°C. Results indicated that the radial temperature difference in the position of torsion element is much lower compared with that of the position of screw elements, no matter before

Figure 5.

Radial and axial temperature distribution for the different screws at 40 r/min. (1) r = 14.5 mm; (2) r = 14.0 mm; (3) r = 13.5 mm; (4) r = 13.0 mm.

#### Figure 6.

Temperature contours (left) and melt temperature profiles (right) across the melt flow with the magnitude of fluctuations for screw B at different x-positions at 40 r/min.

or after the torsion element. It can be concluded that the torsion element can achieve more uniform temperature distribution than the screw element.
