Power for agitator calculation with 3 impellers 2

[JuliusChoi]

Hello,

I am getting the quote for agitator now.
I am comparing the power requirement between different vendors and also comparing those with my calculation.
I found there are big difference between my calculation and their numbers.
I just simply calculate power consumption by P=Np X N^3 X D^5 x density. For agitator with multiple impellers, I just times number of impeller to power consumption (number of impeller X power consumption for single impeller). I also take the safety factor into account. Is there anything I am missing now?
All your comment will be helpful for me and thank you in advance.

Best regards,

Julius

 

[LittleInch]

Can you define your Equation please.

Some numbers would also help to see what the difference is. "Agitator" is a bit vague. Power is probably best measured and not calculated.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pierreick]

Hi,
Review your formula, should be D^5.
I will trust calculation from vendor from reputable companies based on your specification sheet.
Edit:
Power number for multiple impellers
Combined power number P0c = P01+(P02+P03) *(P0n/P0)
Po1: bottom impeller power number
P02: 2nd impeller power number
P03: 3rd impeller power number
(P0n/P0) document attached.
**Np= P0 single impeller
P0c = 3 is a bit pessimistic if the impellers (3) are the same, should be 2.7 to 2.8 otherwise 3 if different types.
Power Agitator = P0c* N^3*D^5 *density

reference: Design Guide for Impeller Power Number by M.H. Palmer
Good luck
Pierre

 

[JuliusChoi]

@pierreick You are right. I changed it. Thank you.

 

[pierreick]

Hi
missing document
Pierre

 

[TiCl4]

Not to get too involved, but the power number of the impellers will change based on their proximity to each other. As impeller spacing approaches closer than 1.5X impeller, some of the flow from the top impeller will feed the bottom impeller, lessening the power required. You can imagine that if you take this to an extreme, with one impeller directly above the other, they essentially act as a single impeller.

It's better to ask the OEM, I think.

 

[JuliusChoi]

Thank you so much for all your valuable comments!!

 

[geesaman.d]

Can you define your Equation please.

Some numbers would also help to see what the difference is. "Agitator" is a bit vague. Power is probably best measured and not calculated.

Power numbers of impellers vary widely, and only the agitator supplier is likely to have accurate numbers for that.

Also those power numbers can vary from impeller-to-impeller proximity, proximity to the floor, and fluid viscosity. TiCl4 has already noted this.