It is interesting to investigate the critical Reynolds number
Rec, at which point the IMRs disappeared owing to the
presence of flow perturbations. Nabil Noui-Mehidi et al. (2008)
highlighted the mechanism of IMR disappearance using a
Rushton turbine and they showed that the disappearance
of the IMRs in the system was attributed to two factors:
stretching and shrinking in the presence of perturbations.
A similar mechanism was observed for the impellers used
in our study and our results show that the critical values
of the Reynolds number are highly dependent on impeller
type (refer to Table 2). Under unbaffled condition, among the
impellers, DT6/A-45PBT4 has the smallest critical Rec and the