Simplified calculation for pressure drop for isothermal compressible gas flow 3

[PagoMitch]

Does such a thing exist for O2 at high pressure?
Searched this site, and cannot find anything similar.

I have tried several online calculators for same, with results that vary by an order of magnitude... from 22 psi to 322 psi.
On the TLV website calculator (pretty detailed, and the unit analysis worked out), their calc result (200 psi) is a far cry from their formula that I went through (22 psi)...
Also tried a couple of the Darcy and Iso compressible flow equations in Metric Crane 410 - I could never get the unit analysis to work out.

Conditions:
Client needs 0.7 kg/sec@ 1200 psi. Call it 2520kg/hr.
I have assumed to provide that volume at 1300psi to allow for a ...reasonable...pressure drop.
At 1300 psi = 115 kg/m^3 = 7.2 lb/ft^3 density.
after some conversions = 11.7 ft^3/min (0.0054 m^3/sec) mass flow.

O2 at 1300 psi (89.6 BAR)
Pipeline = Drawn copper at 265LF (81M) at 3/4" ID (19mm) - pipe and O2 tanks are indoors at appx 70-100F (21-38C)
Velocity = 63.6 feet/sec (20 m/sec)
O2 Dynamic viscosity = 0.02125 cP (22.89 x 10^-6 Pa s)
Surface roughness (Epsilon) = 0.0025 mm
Relative Roughness (Epsilon/diameter) = 0.00013
Reynolds #= 2.5Mil, Relative roughness 0.00013, Darcy FF = 0.015
O2 compressibility factor 0.308
O2 molecular weight = 32
Ratio of specific heat "k" = 1.4
Roughness coefficient = 0.0015
Mach # = 0.08; but this was from a site that yielded a pressure drop of 283 psi (???), as well as well as a Reynolds # 2X what I calculated.
A multi-hundred pressure drop for this system just does not feel right...

We have 2-bank O2 Manifold, with H size Cylinders at 2000 psi: so we have lots of P available.

Think I have everything covered above.
I think/thought we fall into the range where Darcy is still applicable; but I cannot seem to make it work.
Can anyone point me to something that has been verified to be reasonably accurate? +/- 10% or so is all I am looking for.

TIA

 

[Caloooomi]

I also get around 220 psi dP, but I was being lazy and shoved it into a process simulator for 19 mm ID copper tubing @ 89 m length.

If you go for a larger tube diameter then the dP won't be as severe (25mm ID gives 50 psi dP for same length), so you will be able to use the cylinder bank for longer before needing to change them out.

 

[PagoMitch]

Thanks again all.

Glad to see my 220 confirmed.
Interestingly enough, we had Swagelok go thru about a dozen gases in this system; they are providing the manifolds and regulators.
For the O2, they came up with 149 PSIG.
For this project, this is now pretty much academic, as we will just be adjusting the regulator to get the desired result.

 

[georgeverghese]

At 225ft of 0.76in id tubing, I get a developed backpressure of 1355psig with an exit press of 1200psig, so dp = 155psi.

 

[katmar]

Even though this has become an academic exercise, it is interesting to investigate why Swagelok would get such a different Delta P from the 220 psi that the rest of us got. It is all about the input data. Here are the principle differences

Pipe ID: Swagelok = 0.76"

Rest of us = 0.742" (18.85 mm)​

Pipe Length: Swagelok = 225'

Rest of us = 266' (81 m)​

Temp in: Swagelok = 70 F

Rest of us = 100 F (38 C)​

Swagelok have not specified the pipe roughness that they used. Most likely they would have used the normally accepted value for drawn piping of 0.0015 mm and not the 0.0025 mm given in the thread.

Using the Swagelok values gives almost exactly 149 psi in the standard isothermal model. They have shown a small temperature drop between inlet and outlet, indicating that they have used the adiabatic model. Under the given conditions the two models should give very similar results.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[pierreick]

Hi,
Agree with Harvey about the calculation using the Adiabatic model. Not sure why Swagelok choses it, long tube, no insulation.

Pierre