Three‐dimensional path line tracking and residence time distribution in fishtail dies

The flow kinematics of power‐law fluids in fishtail dies is studied. A general isothermal three‐dimensional finite element code developed by the authors is used for the flow analysis purpose. The basic geometry of the fishtail die is defined by simple super‐elliptical curves, which allows a smooth transition from a circle to a slit. The three‐dimensional path line and the residence time distribution (RTD) are calculated from the velocity field obtained from the finite element solution of the conservation equations. The effects of the rheological properties and the die geometry on the path line pattern and the residence time distribution are investigated. The results indicate that as both the length of the transition zone and the fishtail angle increases, the residence time distribution becomes more uniform. However, the power‐law index does not affect the residence time distribution significantly.