The features of the IMRs formed in the viscous Newtonian
systems in a stirred tank have been studied in this paper. The
effect of Reynolds number on the IMRs was determined. The
critical Reynolds numbers beyond which IMRs are destroyed
were presented. A pitch-bladed impeller with an alternating
pitch was found more energy efficient than other test
impellers in eliminating IMRs in both baffled and unbaffled
configurations. It was also found that dramatic reduction in
the power consumption could be achieved with installation of
baffles to eliminate IMRs at typically low Reynolds numbers.
The improved energy efficiency was thought related to generation
of more chaotic mixing from the disturbance generated
by the baffles, or impeller blade asymmetry such as alternating
pitch. An energy parameter was introduced to account for
the mixing time scale and the power required in regimes below
the critical Reynolds number, in order to evaluate the energy
efficiency when IMRs are non-existent.