Displacing yield stress fluid by Newtonian fluid in a vertical circular channel

Abstract eng:
We investigate the characteristics of displacement flow of a yield stress fluid by a Newtonian fluid. A neutralized solution of Carbopol, is placed at the bottom of a vertical pipe, displaced by pumping Newtonian fluid downwards from the top. During the displacement, 3 flow regimes are identified: central-type, slump-type and turbulent. Central-type displacements left non-uniform residual layer at the wall. Slump-type displacement normally have two fronts moving at different speeds, sometimes with Carbopol moving backwards against the imposed flow (when the Atwood number (At) is positive and the imposed velocity low). Turbulent mixing results in no discernible boundary between the displacing and displaced fluids, typically for Re > 8000. In some experiments with low velocity and negative At, the initial developing phase forms at the beginning of the experiment and a portion of initial phase stays until the end of the experiment without being displaced.

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