Hole amount and size calculation for perforated pipe (Sparger) 1

[Kalle1202]

Hey everyone,

I am trying to calculate how many holes I need for an equal air release in a perforated pipe scenario.
I have a 5 HP blower with max. 2,500CFM airflow at 1.000in SP. I would like to have a hole size of 1/2" if possible.
You can find the pipe geometry attached.(everything is horizontal) I would like to have the same hole size everywhere and the holes have to be on the bottom of the distributor pipes. The surrounding medium is air.

I calculated that at 1.000in-SP the pressure difference to the surrounding air is 0.0364psig.
Therefore the airflow through each hole is = 1/60 * 4.17 * C * (10/4.654)^2 * 103.08kpa * (1- (103.08-101.325)/103.08)/(3*0.71*0.72)) * sqrt((103.08-101.325)/103.08)/(20+273.15)
= 0.2567 * 103.08kpa * (1- (103.08-101.325)/103.08)/(3*0.71*0.72)) * sqrt((103.08-101.325)/103.08)/(20+273.15)
= 0.2567 * 103.08kpa * 0.989 * sqrt((103.08-101.325)/103.08)/(20+273.15)
= 26.17 * 0.00762
I just assumed 0.8 for the discharge coefficient. Then I get to an airflow of 0.2Nm3/min which equals 7SCFM or 357 holes
However when I type my numbers into this formula here

https://www.tlv.com/global/ME/calculator/air-flow-rate-through-orifice.html?advanced=on

I geta result of 2.65SCFM per hole or 944 holes total.

Where is my mistake? And can I calculate it in this way?

 

[Kalle1202]

Attachment

 

[Latexman]

You didn't mention what looks like 4" pipes of progressively longer length. Are they connected to the sparger?

Good Luck,
Latexman

 

[chicopee]

Are you trying to get the same air flow (CFM) thru each pipe and what do you consider to be an appropriate number of discharge pipes? If you have answers to these two questions then you should be able to calculate the pressure drop not exceeding 1"SP from the fan outlet (considering no pressure drop in fan inlet) to each pipe outlet. There are other ways to figure out this problem depending on the CFM for each pipe and the number of appropriate pipes.

 

[Kalle1202]

Hey Chicopee yes we want the same airflow through each distribution pipe. We have in total 16 discharge pipes with the attached lengths. (all 4" diameter)

 

[katmar]

If you want all of the 16 holes in the manifold to be the same size then the only sensible way to do it is to ensure that virtually all the pressure developed by the fan is used by the drop through the holes, and the pressure drops along the manifold and through the distribution pipes are effectively negligible. If you want 156 scfm through a hole with 1" water column pressure drop you are looking at about 3.5" diameter. The manifold probably needs to be 16 or 18" ID, and the distribution pipes 8".

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[chicopee]

katmar, The 156 CFM thru each 4"pipe will be under 1 inH2O because, there will be pressure drop at the inlet of the pump and its outlet connection to the 10" trunk line, another pressure drop at the T connection where flow is to be split equally to both 10" trunk line, pressure drop within the 8" segment of trunk line between each 4" lateral lines, futher pressure drop at connections between sparger hole connections and their respective 4" lateral lines and lastly pressure drop within the 4" lateral lines. In essence the total pressure drop of 1"H2O is between the blower suction intake and the 4"lateral line endpoints.

 

[katmar]

chicopee - yes, I agree that the pressure drops in the 4" lines will be less than 1" H2O. By my calculation it is about 0.5" in the longest (58 ft) line. But if you want the diameters of the holes in the 10" manifold to all be the same then you want to use up all the pressure drop across these holes.

There are 16 possible routes for the air to follow. Thanks to symmetry we only have to analyze 8 of them. The pressure drop through each of these routes is the same (i.e. 1" H2O), and the aim is to have the flow rate the same (i.e. 156 scfm) at each exit point. The pressure drop for each route is made up of 3 components, ie from the middle of the 10" manifold to the hole, through the hole, and from the hole to atmosphere via the 4" pipe. All the flow rates are known so it is possible to calculate the first and last of these components, and then by difference determine the pressure drop through each hole and therefore size that hole.

This is all far too much work for me. I prefer to make the first and last components negligible, making the pressure drop through the hole 1" H2O in all cases. Total pressure drop for any of the routes = negligible + 1 + negligible = 1.

Having all the holes the same size also reduces the chances of fabrication errors.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[IFRs]

It also matters how close to each other you need the flow and pressure drop to be.
1" H2O within .0001" H2o is far different from 1" H2O within .5" H2O
Same for flow - does the flow have to be equal to 1 part in a 1000 or 1 part in 1?