Pressure drop through perforated pipe inlet 1

[Rodddxl]

I am pulling water out of a 500 psi pressure vessel with a 12" perforated pipe. I need to calculate the pressure drop across the perforated holes. Essentially, it is a sparge tube flowing in the reverse direction. Would a sparge tube pressure drop calculation still be accurate with the reverse flow?

 

[LittleInch]

Sparging is normally gas into liquid so liquid in reverse flow is quite different.

At 500 psi I'm struggling to work out why you need to know to any level of accuracy.

How many holes?
Total area of holes compared to area of pipe?
Flow velocity at end of pipe?
Pressure in pipe?
Multi hole pipes are not simple and depends on a lot of factors

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

 

[Rodddxl]

36 holes (3 rows of 12) at 1.375" diameter each. Flow rate is 853 gpm. At this point in the design, we are working on what discharge pressure is possible with a 500 psi pressure vessel. If it turns out to be too low (the client hasn't provided this to date), we will have to work the calculations from the discharge back to find the required pressure in the vessel.

All the pressure drops are important because the system we are using to generate the pressure represents a significant portion of the cost of the unit. Also, the flow through perforations occurs along multiple points in the system, so it is possible for the pressure drop to become significant.

 

[Latexman]

Can you attach a sketch? "The flow through perforations occurs along multiple points in the system" is confusing me.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Rodddxl]

Because of nondisclosure restrictions, I am unable to attach a sketch of the system. I realize that makes it a bit challenging for you all.

There are multiple vessels in series and the system uses the same perforation pattern and flow rate for various inlet and outlet points along the line. Hope that clarifies a little.

 

[Latexman]

I *think* so. I assume each pull point is the 36 holes (3 rows of 12) at 1.375" diameter each on a 12" pipe. If you treat the pressure drop at the pull point like an orifice (or a number of orifices in parallel), then I think it would be about the same no matter the direction of flow. I say this because our pressure drop equation for such items is based on the orifice velocity.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[mk3223]

What's the purpose to have a perforated pipe in the the water outlet of the vessel? Does it work as a strainer?
IMO, the pressure drop for each hole on the perforated pipe may be depended on the water flow pattern inside the vessel and the location of the hole on the pipe. If the flow pattern can't be changed, you may want to increase the hole number or size to reduce the pressure drop.

 

[MikeHalloran]

I get 1.09 feet of water.
Calculated Cv for the array is 1223.64 gpm/sqrt(psid).
Velocity in each hole is 3.49 mph.
That assumes all holes are at the same elevation, in a 'thin' sheet, and are punched or drilled 'clean', with no burrs, no chamfer, and no radius.

Machinists and fabricators often round off hole edges so they will 'flow better', but that makes the calculations impossible/erroneous because edge effects are hugely sensitive to the actual edge conditions. Better to avoid any mention of fluid metering on the shop drawings.






Mike Halloran
Pembroke Pines, FL, USA

 

[Latexman]

I got 1.14 feet of water. I used [Δ]P (psi) = 2.8(V_orifice)^2.8 .

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Rodddxl]

The reason for the perforations is due to structural integrity considerations.

I was considering doing each hole from an orifice approach as well.

Thank you all for your time, input, and expertise.

 

[LittleInch]

Your area of the holes is approximately half of your 12" pipe area. Without doing the sums I agree with those that have that the pressure losses at that flowrate is very low.

If this is a dead end pipe then the flow will be constantly changing and the pressure loss across each hole very small, but different for each set of holes as you go down the pipe from the end to the ooen end.

I don't get the series of vessels bit

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

 

[georgeverghese]

There are expressions for perforated pipe pressure drop in Perry 6th edn

a) in the chapter on fluid transport
b) in the chapter on gas liquid contacting systems - this may for sparger systems only if I remember correctly (forward flow).

McGraw Hill and / or the section editor have ripped out the former in the 7th edition.