Viscous Shear Heating in a Cylindrical or Slit Die

When a very viscous molten polymer is forced to flow through a slit or capillary die, viscous shear heating can become significant above a certain critical value of y or ct. Under such situations, nonlinear profiles of wall normal stress in a slit or capillary die may be observed, as described in the preceding section. Therefore, continuous-flow capillary/slit rheometry is limited to y or a, below which viscous shear heating can be neglected. 

The upper limit of y or a above which the extent of viscous shear heating becomes significant can be predicted theoretically by solving the following equations of momentum and heat transfer in a slit die  

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