COMBINED EFFECT OF SEDIMENTATION-VELOCITY FLUCTUATION AND SELF-SHARPENING ON INTERFACE BROADENING

The velocity fluctuation of sedimenting noncolloidal particles leads to the broadening of the interface region. In order to determine the sedimentation velocity fluctuation from the interface broadening quantitatively, the self-sharpening that reduces the broadening has to be considered simultaneously. If the velocity fluctuation effect is described by a diffusion process, the equation of mass conservation of sedimenting particles includes both of these two effects and the functional dependency of the diffusion coefficient on volume fraction is inferred from this equation. The application of the equation of mass conservation requires the volume fraction data as a function of both position and time, which is acquired by NMR-CT. The experimental results show that the interface broadening due to the velocity fluctuation is reduced substantially by the self-sharpening effect in the volume fraction range from 0.01 to 0.15. The dimensionless diffusion coefficient increases as volume fraction increases up to 0.04 where the diffusion coefficient reaches its maximum value, 22, and decreases slowly as volume fraction increases further up to 0.15