ITT: Baffles baffle Biggles - Chem Eng

[bigglesworth]

Can someone explain to me what exactly the baffles in a chemical reactor or fermenter do? Wikipedia is startlingly unhelpful on the manner, and my textbook seems to assume I already know what they are.

I can't seem to visualise what a... fin? hydrofoil? does to the flow in the reactor. Google images hasn't helped either.

[Mr_Rose]

Short version:
Increase turbulence == increased mixing == better distribution of heat and reactants.

[++$_]

My intuitive understanding as a non-engineer:

Without baffles, all the stuff in your reactor will have a tendency to just go around and around. That seems unlikely to result in rapid homogeneous mixing. For example, once the entire contents of the reactor are rotating with the impeller, your impeller stops being effective since it is no longer moving very fast relative to the fluid.

[bigglesworth]

So it stops vortexing then.

[PhDFluff]

If you're interested I can fix you up with a picture of the baffles we use in the fermentors in our lab.

[bigglesworth]

That would be very kind of you.

[Zamfir]

Helpful video:

http://www.youtube.com/watch?v=6E2-y96uYR4&noredirect=1

[bigglesworth]

Superb! Thanks Zamfir.

[Zamfir]

What's especially nice to see is that the baffle does not create some intense local flow phenomenon, with lots of mixing near the baffle. It mostly forces a 'bend' in the flow, and that upsets the entire flow pattern.

In a sense, it's not that the baffle does something very special, it's that a smooth cylindrical tank allows an unusually smooth and stable flow pattern. Any trubulence-creating disturbance is an improvement. But it has to be a disturbance that doesn't create a shadow dead zone near it, where flow can reside without being thrown bak into the overall pattern.

[PhDFluff]

Here's a couple of pictures of a fermentor as promised.

[bigglesworth]

Thank you. It is good to note that, as per my textbook in front of me, the width of the baffles seem to be about 10% of the vessel diameter. And that no more than four are necessary.

[PhDFluff]

Thank you. It is good to note that, as per my textbook in front of me, the width of the baffles seem to be about 10% of the vessel diameter. And that no more than four are necessary.

That seems to be accurate. In my baffle there's three of them about 1-2cm wide. In baffled cell cultivation e-flasks you usually have four.