The Role of Baffles in a Reactor: Increasing Mixing & Heat Exchange

[gfd43tg]

Hello,

I know the use of baffles in a shell and tube heat exchanger will guide the shell-side fluid as it navigates through the shell, but I saw baffles are also used in CSTRs to help with mixing.

This is clearly illustrated with the diagram

where one can see that the baffle is directing the shell fluid up and down, increasing the time it spends inside the exchanger, thus absorbs more heat from the tube side fluid, hence heat exchange. Very useful indeed.

According to wikipedia, the use of a baffle in a tank reactor is

In a chemical reactor, baffles are often attached to the interior walls to promote mixing[2] and thus increase heat transfer and possibly chemical reaction rates.

However, with the diagram here of a stirred reactor, I don't see how having some blocks on the side actually do anything? Is it not the agitator that is doing the mixing? What good is the baffle for?

 

[Chestermiller]

The ideal CSTR model assumes that the fluid in the reactor is perfectly mixed, and that there are no concentration gradients inside the reactor. However, in a real-world stirred tank reactor, you won't have perfect mixing and there will be concentration gradients present. The baffles contribute additional disturbance to the flow created by the mixer, and provide more effective mixing. So, including the baffles brings you closer to the ideal of perfect mixing.

Chet

 

[gfd43tg]

But how does sticking them inside there actually increase mixing? They look like rectangles that just stick to the side of the wall

 

[billy_joule]

Ever stirred a cup of tea or coffee and had the entire mass of fluid start rotating in the cup? As soon as it happens there is not much turbulence right? You can take your spoon out and watch it continue to spin for some time.
Imagine having baffles on the inside of your cup, how would that change the mixing?

 

[gfd43tg]

I think I see what you are saying now, it just breaks up the flow and increases turbulence. Thanks