Miscible density-stable displacement flows in inclined tube

We study density-stable laminar miscible displacement flow of two iso-viscous Newtonian fluids in an inclined pipe (diameter D̂). We present a wide range of novel experimental results. We illustrate the non-monotone relation in displacement efficiency at the density difference moves from positive (density unstable) to negative (density stable), the efficiency being minimal for iso-dense fluids. The density stable configuration has been found to produce highly efficient displacements, with the bulk of the interface moving steadily at the mean velocity. The streamwise length of the stretched interface, or stretch length L̂ , is measured over a wide range of parameters. The stretch length increases with the mean flow velocity, increases with inclination β from vertical, decreases with density difference, and increases with viscosity. Our data are well represented by the scaled expression L − tanβ = −3680/χ , where χ is the ratio of buoyancy and viscous stresses. C © 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4766197]