Perforated Pipe Question 3

[melerine24]

Im looking to do some calculations on a pump hooked up to a perforated pipe in a tank. The reason is purely for recirculation and agitation. I cannot find any formulas or guides as to how many hole and what size is a safe range( or desirable range) for a given pump and tank size.

Any help or guidance to formulas and/or text would be greatly appreciated.

 

[EmmanuelTop]

If you want uniform distribution of liquid through the holes, pressure drop across the sparger pipe must be much less than pressure drop across each sparger orifice. Recommendation from Perry's ChE Handbook is to keep pressure drop across the sparger <10% of pressure drop across the sparger hole.

The total cross-sectional area of all orifices together is defined based on pressure drop (backpressure) you can afford for the pump, and considering agitation requirements as well. Higher pressure drop increases discharge velocity from each hole, but it imposes higher backpressure on the pump. So you must balance the system accordingly.
See some info at

http://www.mottcorp.com/resource/pdf/sparger_design_guide.pdf

Dejan IVANOVIC
Process Engineer, MSChE

 

[melerine24]

Thanks for the info,
I should make it clear as well that I am recirculating the fluid into itself. There is no gas or air used.

 

[EmmanuelTop]

The pressure drop principle still applies. The questions are:

- How much pressure drop can you afford? --> this will define the size/number of the sparger orifices
- What controls are available on the pump discharge? Is there a net discharge flow out of the system, or everything get recirculated back to the tank? --> if there are no other controls, you have to match the circuit+sparger pressure drop with the pump curve in order to have the desired flow, and also to prevent from pump off-the-curve conditions.



Dejan IVANOVIC
Process Engineer, MSChE

 

[melerine24]

Thanks again for responding,

I am unsure of the exact pressure drop I can afford but a rough estimate would be 7-10 psi.
Also all fluid is discharged back into the tank, a control valve is in place for flow control but all fluid is routed back to the tank.

The data I have so far is

Pump:
Max flow- 15gpm
Max Pressure- 100psi

Pipe data:
1 1/4"
80 holes, 3/16"
24 foot long

 

[EdStainless]

But what is the BEP for the pump?
You want to size the holes so that the pump runs at it most efficient point. This isn't just to save power, pumps last longer when you operate them this way.
If the holes are oversized, then you will need to throttle the pump discharge to keep it running in range, then the velocity out of the holes will be very low and you will get little mixing.
Will the level in the tank vary? you may meed to allow for this also.

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P.E. Metallurgy, Plymouth Tube

 

[EmmanuelTop]

The attached article should provide you with the calculation method you need.
Also refer to Perry's ChE Handbook, Section 6, perforated pipe distributors.

Dejan IVANOVIC
Process Engineer, MSChE

 

[melerine24]

Thank you EmmanuelTop,
I believe this is exactly the calculation I am looking for.
I appreciate you're guidance.

 

[bimr]

That is the design of a pipe sparger, not the design of a tank mixing system.

You have left out many details.

1. Is the sparger on the suction or discharge.
2. Volume of tank to be mixed.
3. Fluid properties.

 

[melerine24]

The file provided is exactly the scenario I have. The literature and references showed the calculation needed to size the holes and how many is needed.

but for your information:
1, Discharge
2, 4200 GAL
3, Caustic soda approx. 30% solution

 

[EdStainless]

Of course that just leaves the selection of materials.
Make sure to look at trace impurities.

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P.E. Metallurgy, Plymouth Tube

 

[bimr]

With the little amount of energy that you are adding, the mixing will not be effective.

 

[melerine24]

Can any of you suggest a proper way to gauge how much flow is desired to get good mixing?
I have determined that I will replace the existing perforated pipe and install a new one.

It will be 2.5" diameter pipe with 60 3/16" holes and 24 feet long.
Currently with a 20 GPM pump I am getting a average orifice velocity of 3.87 ft/s.

Any literature or guidance is appreciated

 

[katmar]

The usual way to use recirculation to mix a tank is to use a jet (venturi) rather than a sparger. There are several proprietary designs available, or you may find a rule-of-thumb somewhere to design your own. Do an internet search for "jet mixing".

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"