How Do You Calculate Choked Flow of Propane Based on Natural Gas Parameters?

[cjm181]

Homework Statement

Calculate the equivalent choked flow of propane through a particular valve if the choked flow of natural gas through it is 10 litres s–1.The relative density* of propane is 1.45 and that natural gas is 0.65.

Homework Equations

Kvf = qv (SQRT d/DeltaP) ...1

d is fluids relative density to water / air
P is pressure

Kvf = (SQRTd) x Kvr ......2

where Kvf is valve coefficient of actual gas,
Kvr reference gas

qvf = qvr (SQRT Pr/Pf) ......3

q is volumetric flow rate
Pr is density of ref gas
Pf density of actual gas

qvf = qvr (SQRT 1/d)

The Attempt at a Solution

Not really sure where to start with this. The confusion is because I am comparing a gas (propane) to another gas other than air.

I know I need to find qvf. I am a bit lost with this. Can anyone point me in the right direction or give me a hint please?

Kr
Craig

 

[cjm181]

I think the answer is:
qvf = qvr (SQRT 1/d)
=10 * (SQRT 1/1.45)
=10 * 0.83
=8.03litres/s

Is this correct? I think this works because the equation uses densities relative to air.

I am worried because I have an example of a similar question that uses the above, only it states the chocked flow is with air. What the concern is the equation does not use the density of natural gas. So I am thinking this formula is tied to air as the reference gas. so should I use this formula?

qvf = qvr (SQRT Pr/Pf)
=10 (SQRT 0.65/1.45)
=6.70litres/s.

The answer of 6.7 looks better to me, given the density of NG is 0.65 and Propane 1.45.

Are any of these correct?

Thanks

 

[clh99]

hello, did you ever figure out if either the 6.7litre/s or 8.03litre/s is correct? I am at exactly the same point as you and unsure which value to use