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

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SUMMARY

The calculation of choked flow for propane based on natural gas parameters involves using specific equations that relate volumetric flow rates and relative densities. The relevant equations are qvf = qvr (SQRT 1/d) and qvf = qvr (SQRT Pr/Pf). In this discussion, two potential flow rates were calculated: 8.03 litres/s using the first equation and 6.70 litres/s using the second equation. The latter is deemed more accurate as it incorporates the densities of both gases, confirming that the density of natural gas (0.65) and propane (1.45) are essential for accurate calculations.

PREREQUISITES
  • Understanding of choked flow concepts in gas dynamics
  • Familiarity with volumetric flow rate calculations
  • Knowledge of relative density and its implications in gas flow
  • Proficiency in applying equations related to gas flow coefficients
NEXT STEPS
  • Study the derivation and application of the equation qvf = qvr (SQRT Pr/Pf)
  • Learn about the properties of gases, focusing on relative density and its impact on flow rates
  • Explore the concept of choked flow in different gas types and their specific equations
  • Investigate the effects of pressure variations on gas flow calculations
USEFUL FOR

This discussion is beneficial for chemical engineers, process engineers, and anyone involved in gas flow calculations, particularly in applications involving propane and natural gas systems.

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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
 
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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
 
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
 

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