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

In summary, the question asks for the equivalent choked flow of propane through a valve, given the choked flow of natural gas is 10 litres/s. The equations used in this calculation include Kvf = qv (SQRT d/DeltaP), Kvf = (SQRTd) x Kvr, and qvf = qvr (SQRT Pr/Pf). Using the relative densities of propane and natural gas (1.45 and 0.65, respectively), the possible solutions are 8.03 litres/s and 6.7 litres/s. It is unclear which value is the correct one to use, as there is confusion over whether the equation is tied to air as the reference gas or not.
  • #1
cjm181
69
1

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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  • #2
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
 
  • #3
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
 

1. What is choked flow?

Choked flow is a phenomenon that occurs when the flow rate of a fluid through a valve reaches its maximum rate, and any further decrease in pressure or increase in temperature will not result in an increase in flow rate.

2. How does choked flow affect valve performance?

Choked flow can significantly impact the performance of a valve, as it limits the maximum flow rate that can be achieved. This can result in decreased efficiency and accuracy in controlling the flow of a fluid.

3. What factors contribute to choked flow through a valve?

The main factors that contribute to choked flow through a valve are the fluid properties, such as density and viscosity, and the size and shape of the valve orifice. Additionally, the upstream and downstream pressure differentials and temperature also play a role.

4. How can choked flow be prevented?

To prevent choked flow, the valve can be designed with a larger orifice size, which will allow for a higher maximum flow rate. Alternatively, the upstream pressure can be decreased or the downstream pressure can be increased to decrease the pressure differential and prevent choked flow.

5. What are the implications of choked flow in industrial processes?

Choked flow can have significant implications in industrial processes, as it can lead to decreased efficiency, inaccuracies in flow control, and potential damage to equipment. It is important for engineers to consider the potential for choked flow when designing and operating systems that involve fluid flow through valves.

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