Annular lineal Couette-Poiseuille flow of viscoplastic fluids

The laminar axial flow of non-Newtonian fluids obeying Robertson-Stiff model in concentric annuli is analyzed. Flow is caused simultaneously by the inner cylinder moving along its axis and by the pressure gradient imposed in the axial direction. Both cases - either pressure gradient assists to the moving cylinder or opposes - are considered. All possible cases with respect to the possible positions of the plug flow regions are uniquely diversified through the derived analytical criteria using the entry (geometrical, kinematical and rheological) parameters. For each possible case there is derived the explicit analytical expression for the volumetric flow rate.