A Numerical Simulation of the Temperature Fields in a Capillary with Consideration of the Viscous Heat Generation and a Study on the Measured Viscosity Data

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A numerical simulation of the non-isothermal flow of polymer melts in a capillary was performed with consideration of the effects of viscous heat generation using the finite element method. The constitutive model for polymer melt that we used was the Carreau model with a temperature-dependent viscosity. We studied the effect of viscous heat generation on the viscosity data measured by the capillary viscometer by comparison between the measured viscosity which involved the effect of viscous heat generation and the corrected viscosity from which the effect was removed. The measured viscosity was lower than the corrected viscosity at the wall shear rate γw above 102s-1 and this difference increased with increasing γw. It was predicted that the corrected viscosity was two times as much as the measured viscosity at γw=104s-1 and it was found that the effect of viscous heat generation on viscosity data could not be neglected in the high shear rate region. Also, the temperature rise near the wall reached 50°C when L/R=16 (L: capillary length, R: capillary radius) at γw=104s-1 but near the center of the capillary, the temperature rise was negligible. Therefore a temperature profile developed across the cross-section in the flow direction and the velocity profile changed with temperature profiles.
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