Exit Effects in Non-Newtonian Liquids. an Experimental Study

An experimental investigation has been carried out on the flow of polymeric materials in the exit region of a circular tube prior to their emergence as a horizontal free jet. The measurement of the complete axial velocity profiles by laser anemometry provided information on changes occurring in the velocity profiles as the liquids approach the tube exit. The experimental results for five Theologically different liquids (glycerol and several aqueous solutions of polymers) demonstrate the existence of an exit region for all the liquids tested at Re_n < 1.0. This exit region starts between 1/₂ and 4/3 of a radius upstream from the exit plane, depending on the solution and the Reynolds number. The velocity profile changes in anticipation of the forthcoming stress discontinuity at the exit by accelerating near the wall and decelerating in the center of the tube. The magnitude of the change in the velocity profile was found to depend on Re_n and to be almost independent of an elasticity number, El.