Experimental measurement of shear-induced diffusion in suspensions using long time data

A method based upon Taylor dispersion theory is used to determine the shear-induced diffusion coefficient in concentrated suspensions. The experiments are performed in a cylindrical Couette device with a suspension consisting of polystyrene spheres in a density-matched solution of glycerin and water. A sequence of several hundred transit times for a single tagged sphere to complete successive orbits within the device is measured. The data are analyzed to compute the azimuthal Taylor dispersion coefficient from which the coefficient of shear-induced diffusivity is obtained. In our experiments the particle Reynolds numbers are script O sign (10^-1). The experimental results are compared to the existing measurements of the shear-induced diffusion coefficient obtained at lower particle Reynolds numbers and based upon short-time data. We And a shear-enhanced diffusion coefficient D_⊥/γ + ̇a² = script O sign(0.1) for a volume fraction of Φ≈0.25; this is comparable to existing results from previous low particle Reynolds number studies (ℛ<10^-3).