1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Choked flow thru a valve

  1. Jan 22, 2017 #1
    1. The problem statement, all variables and given/known data


    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.


    2. Relevant 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)

    3. 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
     
  2. jcsd
  3. Jan 22, 2017 #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
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Choked flow thru a valve
  1. Valve spring (Replies: 3)

  2. Choked gas flow (Replies: 1)

Loading...