Rushton impeller power number question

[Joeppeoj]

I am a biotech process engineer, working on a down scale model of our large scale process.
In the large scale process we are using a 1000L reactor with 3 rushton impellers. We will use a small scale process of 2 L with 2 rushton impellers.
To accurately calculate and justify the stirring speed we need to use in our small scale reactor I need the power number for both rushton impellers (for which I can find quite some information online) And a power number correction factor (you cannot just add up power numbers) does anyone have any information regarding power number correction factors for rushton impellers?

I hope I am in the right forum to ask this, if not, please inform me.

 

[pierreick]

Hi,
take a look at the references underneath :

https://www.sciencedirect.com/topics/engineering/power-number

Good luck
Pierre

 

[TiCl4]

What parameter is important to the process? Shear rate? Tank turnovers/min? Solids suspension? Nothing in agitation scales equally, so first identify what the key parameter is.

 

[Compositepro]

My first thought in down-scaling such a process is to reduce the number of impellers to keep the volume per impeller similar. Then I would scale down impeller diameter. I think one impeller in the two liter reactor would be a better choice.

 

[Joeppeoj]

Thanks Pierreick, this is good information. I haven't found anything on power number correction factor yet.

TiCl4 You're right. I'm trying to scale to keep the same mixing time.

Compositepro, there are calculations to calculate the optimal # of impellers depending on liquid hight and volume. I cannot change the impellers, the only thing I can really vary is the stirring speed.

 

[Latexman]

Power/volume and mixing time are calculated values using correlations for power numbers and mixing numbers. It would simplify your task greatly if a real variable that can be measured directly could be found that is important to the process. Maybe not as important as mixing time, but important enough to not go through the hassle of calculation mixing time. Have you looked at tip speed of the impeller(s)?

Good Luck,
Latexman