references for mixer scale-up?

[biofueler]

I'm looking for any good references or rules-of-thumb for mixer scale up. Are there any rules of thumb for power input required to produce similar mixing intensity in vessles of larger sizes? Apart from being a function of viscosity, etc, is there a simple relationship between power input, assuming similar tank design with respect to baffles and geometry. I know it is very difficult to get uniform mixing in tanks of larger size, but could someone shed some light on the physics behind this?

 

[handee]

Hi bio - yes there are LOTS of relationships, but mixing in many ways remains an empirical science. The main problem is that mixing power requirements increase exponentially with impeller diameter and so it becomes prohibitive to 'match' small scale mixing at large scale. However, you are on the right track. IF the systems are geometrically similar (and impeller diam / tank diameter ratio is a really important parameter here) then very good results can be obtained by matching power input. Specifically, you want to use the 'energy dissipation' usually expressed in W/kg of batch. You can find the equations in any good handbook on industrial mixing.

Fran McConville

 

[m777182]

There are some programs that can help you a lot.The only one that I remember by name is VisiMix, but there are more even complex using computational fluid dynamics.
m777182

 

[quark]

You can get many good and free articles from the following link once you register.

http://www.lightnin-mixers.com/cs_techinfo.asp

Click on Technical Articles

 

[Latexman]

Call your local Chemineer rep and ask them to visit you and bring you two booklets they keep on hand, Liquid Agitation and Advanced Liquid Agitation.

Good luck,
Latexman

 

[StoneCold]

biofueler
You have gotten very good advice so far. I have read the articles from Chemineer and they are good. Fxm is right in that if you have similar geometry then you can look at W/kg as a rough guide to scale up. (I generally use 5HP/500gallons. But we use very violent mixing.)


A good book that I have on mixing called Mixing for the process industries Robert J. McDonough.

If you come back with a little more details we can give you a rough idea.

 

[biofueler]

well for our process, its a delicate balance between maintaining dispersion in a multi-phase system without excess shear causing emulsions to form. So essentially, the trick is trying to get adequate mixing without excess shear. I was targeting a 10HP mixer (adjustable via VSD) for 1000 gallon vessel, but may be limited to 500 gal vessels, which it sounds like a 5HP with VSD would be more than enough)