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# Mixing Time With Two Impellers?

mixing agitation solid dissolution

3 replies to this topic
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### #1 paperjerky

paperjerky

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Posted 23 February 2019 - 03:22 PM

Hello all,

I am trying to calculate the dissolution time of solid particles in some of our tanks. These tanks are not baffled, and they each have two propellers on the same shaft, mounted at a 45 degree angle. Based on literature, and the geometry of our equipment, I wanted to get the Power number from a Power number vs Reynolds number correlation table like the one attached to this message.

However, from my understanding, these graphs are for single impellers/propellers only. How do I account for the fact that my tanks have two propellers?

### #2 clarenceyue

clarenceyue

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Posted 04 March 2019 - 10:21 PM

One suggestion is to divide the tank volume into two portions, each portion to cover the upper and lower impellers. I am assuming that your tank is filled enough to cover the two impellers sufficiently. Although I think others may have more experience with this type of mounting for impellers.

### #3 thorium90

thorium90

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Posted 09 March 2019 - 03:59 AM

If this dissolution time is so important, I would suggest to do a scale model, then ramp up to full size by reynolds number scaling.

If you can't do a model for now, then invest in a CFD model first.

If you are not able to do a CFD or scale model, then the last resort "clarenceyue" has given you is a general solution you can use for now.

### #4 paperjerky

paperjerky

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Posted 10 March 2019 - 12:17 AM

Can't I just add the Power numbers for each of the propellers together? Because they're dimensionless numbers? Would they have the same power number? Because they both have the same RPM, they're in the same tank, and they're in the same solution.

Also, with the reynolds number, would the density be the liquid of the solvent or the solution with the salt? Like if we were using water as the solvent, and we added some salt into it for mixing, would the density be that of water, or that of the salt with water?

Edited by paperjerky, 12 March 2019 - 03:57 AM.