While we often thing we seen it all, we are continually amazed by users.  YouTube user Sidney Seckler has posted a video showing an unusual use for a Parshall flume:  Chemical Mixing!

Alum is added (as a coagulant) to the flow upstream of the flume.  The flow is then accelerated from a slow, sub-critical state in the inlet of the flume to a fast moving, super-critical state in the throat of the flume.

Passing through the throat, the flow expands in the discharge section of the flume.  Expanding and slow, the flow become turbulent, serving to mix the alum into the water before it spills off the end of the flume.

Here much of the mixing is done as the flow exits the flume, but in applicaitons where the flow doesn't spill off the end of the flume, the standing wave / turbulence associated with the slowing of the water, occurs in the discharge (or throat) of the flume itself.

 

Source:  YouTube