We study the macromixing behavior of single and multi-orifice-impinging transverse (MOIT) jet mixers with crossflow

in particular

the overall mixing time and the back-splash mixing time of the injected flow with the crossflow

using the PLIF technique. It is found that for a given mixer configuration

there is a critical jet-tocrossflow velocity ratio

r

c

at which the back-splash begins to occur. Further increase in the velocity ratio

r

leads to sharp increase in the back-splash mixing time

which can offset the intensification of the downstream mixing. The dimensionless overall mixing time decreases as

r

increases to reach either a plateau or a local minimum

and the corresponding

r

value represents the optimal velocity ratio

r

opt

for the macromixing. The momentumratio of the two liquid streams is a key factor determining

r

c

and

r

opt

. For a larger scale mixer

a higher momentum ratio is required to achieve the optimal macromixing with the minimum dimensionless overall mixing time.