Limiting factors for sonic velocity with LOW K values.
Limiting factors for sonic velocity with LOW K values.
(OP)
Hello,
Crane's table on page A-22 shows the limiting factors for sonic velocity, but the table ends at low K values < 1.2. Is it accurate if I extrapolate values of K, Y and DP/P?
Thank you.
- Dan
Crane's table on page A-22 shows the limiting factors for sonic velocity, but the table ends at low K values < 1.2. Is it accurate if I extrapolate values of K, Y and DP/P?
Thank you.
- Dan





RE: Limiting factors for sonic velocity with LOW K values.
Good luck,
Latexman
RE: Limiting factors for sonic velocity with LOW K values.
I would like to extrapolate low K values because I want to do a case study for individual components.
Elbows
Valves
Short Pipe
I want to perform hand calculations with a pressure ratio across each single component and then perform a Flowmaster analysis on the component to see the similarity.
For me to perform hand calcs on a single component with a low K value, I need the limiting sonic factor Y for sub K=1.2 components.
So you are saying that extrapolating is ok?
Thanks!
RE: Limiting factors for sonic velocity with LOW K values.
Good luck,
Latexman
RE: Limiting factors for sonic velocity with LOW K values.
Patricia Lougheed
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Limiting factors for sonic velocity with LOW K values.
Than what should I do if I am faced with flow across a component with a K factor that is less than one but a pressure ratio that is large? How would I determine limiting sonic Y?
Thank you again!!
RE: Limiting factors for sonic velocity with LOW K values.
Patricia Lougheed
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Limiting factors for sonic velocity with LOW K values.
If my upstream pressure is 100 psia and downstream is atmosphere then my DP/P is 0.853. If I am applying this to a single 1" diameter elbow with r/d of 3 than my K will be K=12*(0.02) = 0.24.
There is no K value low enough on the table to look up the limiting sonic velocity, but I'm pretty sure it will be sonic because of the small diameter and barely any losses.
Even with a K value of 1.2, the limiting DP/P is 0.552, if I am at 0.853 i would need a K of more than 20 keep it sub sonic.
I just need help calculating the flow rate across this component, and if I cannot find Y, than i cannot use equation 3-20 of crane's.
Thank you again.
RE: Limiting factors for sonic velocity with LOW K values.
Doing a flow model of a valve hanging in mid-air (no inlet or outlet pipe) doesn't do much for me. Seeing the estimated differences these components make in the flow of a real system, does.
Good luck,
Latexman
RE: Limiting factors for sonic velocity with LOW K values.
while you were replying I have done some calculation of an elbow attached to a segment of 10 foot pipe. At that point, it is safe to say that the K value would be > 1.2.
I am not trying to build a real model at this point, i just want to see if the flowmaster theory is close to that of crane's. The only way for me to do this is test a single component at a time between two known pressure sources, and do that calculations by hand to verify.
The reason I am doing this is because I am building my own flow system solver for a specific system.
I want to compare my system to flowmaster v6.5.2. It is just being used to validate, so the relations that flowmaster uses must be the same ones i use or else it will validate nothing for me.
I appreciate all your help. I am slowly understanding what to do now.
We have to think in terms of theory, imagine at this point there is no 'system'. Lets just study each component case by case.
If you must include reality, I can build a scenario that satisfies my cases.
Imagine a huge tank of nitrogen at 100 psia. There is an elbow welded directly to the tank and a valve attached to the elbow. A truck accidentally crashes into the valve and breaks it off, the elbow is now discharging 100 psia nitrogen to the atmosphere.
The flow rate through this elbow can be calculated with equation 3-20. But how do you calculate the limiting parameter Y if the K value of this elbow is 0.24?
Am I missing something?
Please bare with me.
I am a fast learner, I just need more time :)
RE: Limiting factors for sonic velocity with LOW K values.
Patricia Lougheed
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Limiting factors for sonic velocity with LOW K values.
Good luck,
Latexman
RE: Limiting factors for sonic velocity with LOW K values.
IMHO, a single elbow would act more like an orifice than a pipe in your application anyway.
Good luck,
Latexman
RE: Limiting factors for sonic velocity with LOW K values.
Thank you for the info.
Does anyone happen to have the correlation that the table on A-22 is built upon? I want to curve fit the data points but I would much rather have the real correlation.
I need the continuous solution so don't have to use a lookup table.
Thank you!!