6. Experimental validation

The performance of screw with torsion elements in the polymer plasticization process has been verified though numerical analysis. Furthermore, the mixing and heat transfer performances of the newly designed screw configuration based on field synergy principle were evaluated through extrusion runs and experimental data. Materials used were polypropylene (PP) and polystyrene (PS) bi-phase polymer composite mix.

Figure 11 shows the particle size distribution of PS (PP: PS = 100:10, % wt/wt) at the screw outlet; more specifically, Figure 11(a) is that of torsional screw with six torsion elements and Figure 11(b) is that of conventional screw without torsion element. The particle size distribution of PS fits Gaussian distribution. On the other hand, the relative frequencies of particle size in torsion screw are more concentrated in a narrow range [0–50 μm] than those in conventional screw. This can be further validated from the scanning electron microscope (SEM) pictures shown in Figure 11(a) and Figure 11(b). SEM pictures clearly show that the particles of PS in torsional screw are finer and the particle sizes are smaller than those in conventional Multi-Field Synergy Process for Polymer Plasticization: A Novel Design Concept for Screw… DOI: http://dx.doi.org/10.5772/intechopen.89616

Figure 11. Particle size distribution in a PP/PS bi-phase composite in the outlet of the screws.

Figure 12.

5.3 Fluid flow behavior

Thermosoftening Plastics

cross section of the torsion element (b).

Figure 10.

elements as shown in Figure 10.

convection in the screw channel.

6. Experimental validation

mer composite mix.

28

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

The streamline contours in screws A, B, and E at a screw speed of 40 r/min in the axial direction (a) and the

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

Therefore, it can be inferred that the torsion element improves the synergy between velocity and temperature gradient by inducing torsional flow, and then

The performance of screw with torsion elements in the polymer plasticization process has been verified though numerical analysis. Furthermore, the mixing and heat transfer performances of the newly designed screw configuration based on field synergy principle were evaluated through extrusion runs and experimental data. Materials used were polypropylene (PP) and polystyrene (PS) bi-phase poly-

Figure 11 shows the particle size distribution of PS (PP: PS = 100:10, % wt/wt) at the screw outlet; more specifically, Figure 11(a) is that of torsional screw with six torsion elements and Figure 11(b) is that of conventional screw without torsion element. The particle size distribution of PS fits Gaussian distribution. On the other hand, the relative frequencies of particle size in torsion screw are more concentrated in a narrow range [0–50 μm] than those in conventional screw. This can be further validated from the scanning electron microscope (SEM) pictures shown in Figure 11(a) and Figure 11(b). SEM pictures clearly show that the particles of PS in torsional screw are finer and the particle sizes are smaller than those in conventional

enhances heat transfer in the screw plasticization process.

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

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 performance.

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 simulation results.

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

polymer melt. In addition, the radial temperature difference of torsional screw is 15° C, whereas the radial temperature difference of conventional screw is 20°C, which is 25% higher than that of torsional screw. As the experiment data indicate that the radial temperature difference of melt decreases in the torsional configured screw, it can be concluded that the torsional configuration has a superior heat and mass transfer performance to achieve better temperature distribution than traditional screw, which is also in agreement with the simulation results.

δ<sup>t</sup> thermal boundary layer thickness, m

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

K heat transfer coefficient, W/(m2K)

α synergy angle between the velocity gradient

β synergy angle between the temperature gradi-

B temperature sensibility coefficient, K<sup>1</sup>

and the velocity, °

ent and the velocity, °

\*

1 College of Mechanical and Electrical Engineering, Beijing University of Chemical

2 Centre for Biocomposites and Biomaterial Processing, Department of Mechanical

3 College of Electromechanical Engineering, Qingdao University of Science and

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Industrial Engineering, University of Toronto, Toronto, ON, Canada

U velocity vector, m/s

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

μ fluid viscosity, Pas

Re Reynolds number Eu Euler number Pr Prandtl number Nu Nusselt number

P pressure, Pa

γ\_ shear rate, s<sup>1</sup> t natural time, s

Ranran Jian1,2, Hongbo Chen3 and Weimin Yang1

\*Address all correspondence to: yangwmr@gmail.com

provided the original work is properly cited.

Author details

Technology, Beijing, China

Technology, Qingdao, China

31

η apparent viscosity, Pas η<sup>0</sup> zero shear viscosity, Pas

n non-Newtonian index T0 reference temperature, K

∇U velocity gradient vector, s<sup>1</sup> ∇T temperature gradient vector, K/m vm mean velocity of fluid, m/s
