Shear thinning temperature

Next, we explore some nonisothermal effects on of a shear-thinning temperature-dependent fluid in parallel plate flow and screw channels. The following example explores simple temperature dependent drag flow. 

Other Factors Affecting the Viscosity of Dispersions. Factors other than concentration affect the viscosity of dispersions. A dispersion of nonspherical particles tends to be more viscous than predicted if the Brownian motion is great enough to maintain a random orientation of the particles. However, at low temperatures or high solvent viscosities, the Brownian motion is small and the particle alignment in flow (streamlining) results in unexpectedly lower viscosities. This is a form of shear thinning. 

PTT exhibits melt rheological behavior similar to that of PET. At low shear rates the melt is nearly Newtonian. It shear-thins when the shear rate is >1000s 1 (Figure 11.10) [68], At the melt processing temperatures of PET, 290°C, and of PTT, 260°C, both polymers have similar viscosities of about 200Pas. However, PTT has a lower non-Newtonian index than PET at high shear rates. The flow behavior can be modeled by the Bueche equation, as follows ... 

The focus of this evaluation is on the results that were reported using four different resins [52] PC resin, LLDPE resin, EAA copolymer, and an LDPE resin. The shear viscosities for the resins at selected processing temperatures are shown in Pig. 7.17 and were modeled using the power law model provided by Eq. 7.42. The parameters for the model are given in Table 7.3. As shown in Pig. 7.17 and the n values in Table 7.3, the PC resin shear-thinned the least while the EDPE resin shear-thinned the most. The LLDPE and EAA resins have n values between those for the PC and LDPE resins. The melt density for the LDPE and LLDPE resins at 240 °C is 735 kg/mT The melt density of the EAA resin at 220 °C was 785 kg/m and the melt density of the PC resin at 280 °C was 1073 kg/mT... 

The predictions for a typical highly shear-thinning PS resin are shown in Fig. 7.38. The difference in predicted discharge temperature was not as dramatic for the different rotation cases. Like the PC resin and as expected, the melt temperature increase for the PS resin was always higher for the barrel rotation case. As shown by Fig. 7.38, the melt temperature increased by 22 °C for barrel rotation while it increased 19 °C for the screw rotation case. Thus, the melt temperature Increase for screw rotation was about 86% of the temperature increase for barrei... 

Figure 6.56 presents a comparison of the pressure at the gate for the Newtonian and shear thinning case. The figure also shows the effect of temperature [1], We can see the effect that the cooling has on the pressure requirements. This is caused by a reduction of thickness due to the growth of a solidified layer on the mold surface, as well as an increase in viscosity due to a drop in overall temperature. For a better comparison, Fig. 6.57 presents the pressure requirements for the shear thinning and non-isothermal cases [1],... 

Power law model fluid with temperature dependent viscosity m0 = e( a(-T Tm The rate of melting is strongly dependent on the shear thinning behavior and the temperature dependent viscosity of the polymer melt. However, we can simplify the problem significantly by assuming that the viscous dissipation is low enough that the temperature profile used to compute the viscosity is linear, i.e.,... 

Summarizing, the model of the screw channel flow is governed by eqns. (8.99), (8.105) and (8.106) with boundary conditions eqns. (8.100), (8.101) and (8.104). The constitutive equation that was used by Griffith is a temperature dependent shear thinning fluid described by... 

Figures 8.37 and 8.38 [9] present velocity and temperature fields across the thickness, respectively, for various values of Br, and forn = 1 and n = 0.6. Griffith calculated the screw characteristic curves for Newtonian and non-Newtonian shear thinning fluids using various power law indices. Figure 8.39 presents these results and compares them to experiments performed with a carboxyl vinyl polymer (n = 0.2) and corn starch (n = 1).

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