5.3 Fluid flow behavior

As stated previously, the synergy effect between velocity and temperature gradient in the torsion element is realized by constructing a spiral or torsional flow in the flow field. In order to verify the existence of torsional-spiral shaped flow, we investigated the fluid flow characteristics in the region of both torsion and screw elements as shown in Figure 10.

Figure 10(a) shows the streamline contours along the axial direction for screws A, B, and E. We can see that spiral-shaped flow occurs in the position of torsion elements for both screws A and B, which cannot be achieved in screw E. In this spiral-shaped flow, the velocity directions are changing along the flow direction and mass transfer is enhanced in the radial direction, that is, the synergy angles between velocity and thermal flow fields are no longer perpendicular to each other, which confirms the assumption shown in Figures 1 and 2. Figure 10(b) shows the cross sections in the torsion and screw elements. And results indicated that there are vortexes in the torsion channel, while there are just plug flows without radial convection in the screw channel.

Therefore, it can be inferred that the torsion element improves the synergy between velocity and temperature gradient by inducing torsional flow, and then enhances heat transfer in the screw plasticization process.

screw. Average particle size (Dn), the maximum value, minimum value, and standard deviation of particle size of PS are also calculated and summarized in Figure 11. Results indicate that the Dn, the standard deviation, and maximum value of particle size in torsional screw are much smaller than those in conventional screw. Therefore, the torsional screw with six torsion elements shows good mixing

Heat transfer coefficient (left) and outlet radial temperature distribution (right) of the plasticization system for

Particle size distribution in a PP/PS bi-phase composite in the outlet of the screws.

Multi-Field Synergy Process for Polymer Plasticization: A Novel Design Concept for Screw…

DOI: http://dx.doi.org/10.5772/intechopen.89616

Figure 12 shows the variation of heat transfer coefficient K with screw speed and the outlet radial temperature distribution at 60 r/min for torsional screw and conventional screw. From the heat transfer coefficient K, we can see that the K value improves with screw speed, which is in agreement with Figure 7. More interestingly, the K value for torsional screw is higher than that for conventional screw, indicating that the torsional screw with six torsion elements shows better heat transfer capability than that of the conventional screw. Therefore, we can confirm that the configuration of torsion element designed based on field synergy principle can in fact enhance heat transfer, which is in agreement with the simula-

From the outlet radial temperature distribution, it can be found that the melt temperature in the center of die is higher than the temperature near the barrel walls, which is due to the viscous dissipation of polymers. Therefore, an effective heat transfer is needed in order to evenly distribute the thermal energy among the

performance.

Figure 12.

screws.

Figure 11.

tion results.

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