The shapes of the response curves depend on the mechanisms
involved in the mixing process in the tank . The turbulent mixing involves three
mechanisms: convection, turbulent eddy diffusion and molecular
diffusion. While molecular diffusion is usually negligible in
turbulent flows with respect to macro-mixing, the transport by
convection and turbulent eddy diffusion are active and their
relative contributions rely on the magnitude of the mean velocity
and the level of turbulence. It is extremely difficult to quantify
their relative contributions experimentally and numerical simulation may play a meaningful role in examining this aspect. The
interval between successive concentration peaks depends on the
circulation time, which represents the extent of convective
transport, while the decay of the fluctuations of concentration
indicates the extent of tracer dispersion due to eddy diffusion Higher impeller rotational speed leads to
shorter circulation time (i.e., higher frequency of peaks)