APS DFD 2011 video submission V045
  Inhomogeneous uid mixing in a tilted-rotating cylindrical tank (radius a = 3:5 cm) is shown at Re(17-40) and low capillary numbers. A water and surfactant solu- tion (1% by mass sodium oleate) is dispersed in soybean oil (95% by volume), through varying the rotation rate, and angle of inclination, the rate of mixing is observed. A planar laser is directed down the tank axis to highlight a cross-sectional area of the fluid volume and as the water droplets begin to break up to sizes on the order of the beam width and less, more light is refracted and the mixture is illuminated. Initially, the water breaks up into large droplets that exhibit approximate solid-body rotation about the bottom of the tank. When the total combined volume is below the critical volume of the tank Vcrit = a^3 tan vortex transport of the water occurs more rapidly, breaking up the water into continually smaller droplets in a process that resembles periodic shearing. When the fluid volume is above critical the water will break up and rotate about the bottom of the tank and vortex-induced mixing is much more reticent, if occurring at all. It is noted that shallower angles with respect to the horizontal produce faster mixing while allowing a greater volume of fluid to be mixed at the sub-critical volume given a constant tank size. 
David Swan, Andrew White, Thomas Ward
physics.flu-dyn