Steam Flow in pipes

[firefastball]

Hi there,

Steam is flowing through a pipe DN 100 from 5 barg and released it through the atmosphere.
I'm thinking of how can I calculate the steam flow or velocity in the pipes.
I've been looking through the internet and found two different formulas and I believe these implies to incompressible flow only:

dp = 0.6753*10^6*q^2*L*(1 + 91.4/D) / ρ*D^5
dp = (8*f*D*ρ*L*Q^2)/(pi^2*D^5}---> Darcy–Weisbach equation

Can anyone explain what is the difference between the two and how do I fit it to apply on steam applications?

 

[Latexman]

I recommend you buy Crane Technical Paper No. 410. It is one of the best fluid flow references in the world. It is not expensive. It will show you how to solve this problem and many, many more! Just Google "Crane TP 410" and follow the path to purchase it.

Good luck,
Latexman

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

 

[MJCronin]

" It is one of the best fluid flow references in the world. It is not expensive"

Amen, Latexman, Amen......

I am on my third copy...... worn out the first two....

MJCronin
Sr. Process Engineer

 

[MJCronin]

http://www.flowoffluids.com/

MJCronin
Sr. Process Engineer

 

[Latexman]

I give my working copy to our summer intern when they leave. I buy me a new one, such that I have it before I give the old one away. I cannot be without it!

Good luck,
Latexman

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

 

[katmar]

I don't recognize the first of your 2 formulas, but it appears to be some empirical equation aimed at avoiding calculating a friction factor. These equations were useful in the days before computers and spreadsheets. They have no place in engineering anymore - not even for incompressible flow.

I agree with the advice to purchase the Crane manual. It is a very useful document. For calculating steam flows in most plant situations where the velocities will be in the 50-100 ft/s range you can safely use the isothermal compressible flow equations from Crane. However, in your situation where you are venting to atmosphere you could have much higher velocities and you should check for the possibility of sonic (choked) flow.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[firefastball]

Thanks for the reply.
I definitely need to have the technical manual looking at the reponse here.

 

[davefitz]

The release of compressible gas from 5 barg to atmospheric implies acoustically choked flow , if the root source was an opening in the pressure vessel at least 100 mm diameter. If the root source was a valve whose seat diameter was less than 100 mm then the choked flow would occur at the valve seat and not in the pipe.

For the former case then the Fanno flow equations would be used to compute the flow that is choked by pipe friction, and in the latter case the ANSI equations for flow through a choked valve would be used. It would yet be necessary to confirm the valve back pressure was less than 3 bar a to confirm the valve was yet choked, so the normal pipe pressure drop equations would be needed to confirm the value of the valve backpressure. Basically the procedure would be to assume a flow, then calculate backwards from the pipe exhaust ( at ambient P ) what the valve back pressure would be. The confirm the flow rate through the valve. Through progressive iterations a solution is found.

"Nobody expects the Spanish Inquisition!"