Change in viscosity of test fluids alters principally pumping flow of impeller and therefore influences bulk mixing.

If there is a bulk mixing of the layers of gas in the tube by mechanical stirring or because of a density gradient, mass transfer occurs primarily by the mechanism of forced or natural convection.

Instead of concocting the material in bulk, like mixing batter, the team is developing a process to control the particles' alignment by assembling them in regular arrays.