Process Wednesday: Vortexes aren't good?

Undesirable? (Credit: eHow)

More on the engineering of reactors, this time from Mr. Ozzie Frietas, the technical sales manager for De Dietrich Process Systems:

The patented design of PharmaCore’s new, glasslined OptiMix reactors incorporates three vertical baffles on the walls of the reactor shell. Side baffles are common in metal tanks. They prevent the formation of vortexes that spin the entire fluid mass but do very little actual mixing or shearing. In baffled tanks, on the other hand, the baffles create turbulence that enhances mixing. They also optimize heat transfer, suspension and distribution of solids and gases, and mass transfer.  

Typical glass-lined reactors do not use straight flat baffles due to the challenge of attaching them to the reactor wall and encapsulating them with glass. Instead, they drop one or more baffles from the top head into the reactor. Under some conditions, these top-mounted baffles may not provide enough turbulence to suppress vortex formation. Vortices not only do a poor job of mixing, but they also splash liquid against reactor walls. In heated reactors, splashes soon turn into dried products that are difficult to remove from the reactor wall during
cleanup. 

De Dietrich developed the process to build wall-baffled, glass-lined reactors a few years ago. The company welds the baffles to the reactor wall prior to coating all steel surfaces with glass. The three baffles suppress vortexing and splashing. The symmetry of the three baffle/three mixing blade combination also minimizes bending loads that can deflect the agitator shaft and reduce seal life.

I'm terribly amused to learn that vortices "do a poor job of mixing." In the lab, the presence of a healthy-looking vortex is a sign to a chemist that things are mixing well, not badly. 

But then again, our friend Neal Anderson tells us this, too:

Without baffles, low-viscosity fluids tend to create vortices and swirl with poor mixing; baffles disrupt vortices and promote flow patters that lead to good mixing.

While I'm firmly convinced of the undesirability of removing dried product off the walls of reactors (boy, am I ever!) and the prevention of such, I'd really like to learn more about mixing and what's the best kind of mixing.  Vortices are poor at mixing? Could have fooled me.

Fascinating video from commenter marvinthefish -- I'm convinced!: