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# Calculating N2 flow to equipment

## Calculating N2 flow to equipment

(OP)
I'm trying to determine the amount of nitrogen flowing to various pieces of equipment in SCFM. 1/2" drops lead to pressure gauges just upstream of each regulator. ~5 feet of plastic tubing connect the regulators to the equipment. Inlet and outlet pressures range from 20 PSIG to atmospheric. The pressure for some pieces of equipment are measured with pressure gauges and others were estimated.

I've been looking at Crane TP 410 for equations and have found q=Y*C*A*(2*deltaP/Rho)^.5 for the flow rate of compressible fluids through an orifice. Can I neglect the plastic tubing and use this equation with the inlet regulator pressure and outlet pressure to the equipment to get a flow rate, then convert it to SCFM? Is there a better way to calculate this, like Darcy's formula for compressible flow through an orifice (q'h=1.0312*(Yd^2/Sg)*(deltaP*rho/K)^0.5)?

### RE: Calculating N2 flow to equipment

flowmeters.
Do these flow unrestricted from the regulators? If so then you can use the flow data for them based on pressure.
If there are other valves then you need meters.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

### RE: Calculating N2 flow to equipment

How much N2 flow do you need to go to each equipment? Putting an acrylic rotameter in the N2 line to each equipment is not very expensive. Take a stab at it and do one of them. Then, with that experience, do the rest.

If the gauge was just downstream of the regulator, I think you would get some meaningful results. What flow creates that backpressure in your tubing.

Good luck,
Latexman

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

### RE: Calculating N2 flow to equipment

(OP)
I went back and checked it out and the pressure gauges are at the outlet of the regulators, so they can be ignored. Some of the lines leading from the regulators to the equipment are unrestricted and I'd like to calculate the flow for those.

There are ~100 pieces of equipment using nitrogen so being able to calculate rather than installing flow meters is preferred.

### RE: Calculating N2 flow to equipment

With 100 usage locations the error in calculation could easily be +/-50%
You need to estimate the largest ones and measure those.
For smaller unrestricted ones use the flow coef of the regulators and the pressure drops.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

### RE: Calculating N2 flow to equipment

#### Quote (redeng50)

I went back and checked it out and the pressure gauges are at the outlet of the regulators, so they can be ignored.

Why? Are they so close to zero, they give you no data? You need a gauge with a lower range. If the reading is within the gauge's range, then you've got ΔP and you can characterize the tubing length and fittings and estimate the flow.

Good luck,
Latexman

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

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