Flow of polymer melts through narrow tubes and capillaries

Flow of polymer melts through narrow tubes and capillaries 

For the flow of a Newtonian fluid through a capillary the Hagen-Poiseuille law is  

The equation for the shear stress at the wall is equal for Newtonian and non-Newtonian liquids, but the shear rate at the wall is for non-Newtonian liquids different from that in this equation. 

If the melt is non-Newtonian, corrections have to be made, the Bagley correction and the Rabinowitz correction. 

The first correction is for entrance and end effects and was suggested by Bagley (1957). Due to these effects, in the calculation of the shear stress at the wall one has to use an effective flow length Le(p. 

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