The miscible displacement flow of non-Newtonian fluids is investigated experimentally in a 20 mm diameter pipe. Attention is paid to the effect of the density and viscosity ratios on the non-Newtonian fluid displacement. The effect of the density difference of the two fluids is discussed via a dimensionless parameter called the Atwood number, At. When the current is stabilized by the imposed flow, the ratio of the front velocity, Vf, to the mean flow velocity, V0, does not significantly change with Atwood number, similar to the Newtonian displacement [5]. The viscosity ratio of the two fluids then seems to be a critical factor on the flow field stability. It has previously been established that the increase in the mean flow velocity dampens the Kelvin-Helmholtz-like instabilities in the system [5]. However it may not be the case for the flows with very high viscosity ratios. The mean flow velocity in turn can contribute to the onset of interfacial instabilities as its value increases.

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