HOW TO FIND AIR FLOW IN SEGEMENT

[3243]

Hi, the problem I have to solve is to find the air flow in a segment of a pipe between two regulators of pressure where there is a 1" (length of about 1/2&quot restriction located.
the system is as follows:

First a tank of compressed air, goes thru 2 filters and a pump in a 3" pipe (Here the pressure is 110psi), then the 3"pipe connects to a 6"( Length of about 40') pipe, then the 6" pipe connects to a 3" pipe again, then the 3" pipe is connected to a regulator(1) where we regulate the pressure to 35psi (segement inlet where 1" restriction is located), then it continues in a 3"pipe where a 1" restriction is located( length of about 1/2 inch) and goes back to 3" pipe, then there is a pressure regulator(2) where we regulate the pressure to 27 psi (outlet where 1" restriction located), then it goes to the atmosphere.
the temperature is constant.

What I need to find is how much is the airflow between regulator 1(35psi) and regulator 2(27psi)(this segement where the 1" restriction is located), How can I do this, Do I have to analyse all the system first or is there something else I can do?,

Can you please help me, I thank you very much for your time, if you can tell me anything that can help,

EJ

 

[rbcoulter]

1. Determine the K values for the pipes and fittings between the two pressure regulators. (Be sure to account for the expansions and contractions.)
Add all the K values in to get an overall K value.

2. Use the isothermal compressible flow equation from the Crane Handbook to determine the flow.

 

[3243]

hi, thanks for helping me, I still dont know somethings,
so the equation i have to use is 1-6 on crane handbook, what V1 do I used??? Is this the volume of the pipe from point 1 to point 2. how can I find fL/D, I dont remember the process, Isn't this equation for long pipes???, the segment i am working on is about 6 feet, thanks for your help.
EJ

 

[rbcoulter]

The legend for the symbols is at the beginning
of the Crane Handbook. V1 (with the bar over it) is
the specific volume of fluid in cu.ft/lb. The "1" refers
to the upstream condition. You can assume that
the fL/D is the overall K term. Methods for calculating K values are shown in Appendix A. Assume a friction factor for complete turbulence.

 

[3243]

Hi again, where can I find the crane handbook, because someone sent me some of the pages I needed but not all the ones I need, I need a table to find all the properties, and Cv and Cp and all other numbers I need, also How Do I find the velocity?, I need the ratio,k, of specific heat at const. pressure to specific heat at const. volume, Cp/Cv.
I also dont have the pages A-23 and A-24 , I only have A-25, Is there anyway you can email me this pages, or tell me where to find them online,
thank you for you help
EJ

 

[ve7brz]

Perhaps I'm missing something here, but I see a 35 PSI regulator, a length of 3" pipe, a short 1" restriction, more 3" pipe, a 27 PSI regulator, ?, 1" restriction, ?, atmosphere.

If I'm interpreting this correctly, then your flow will be determined by 27 PSI to atmosphere via ?, 1" restriction, ?. The flow further upstream, between the two regulators, will be the same as the exhaust flow. The velocities at various points can be determined from that according to pipe diameters.

 

[rbcoulter]

Type in "Crane" "Flow of fluids", etc. in a search engine
and it should lead you to their site. This question has been answered before on these forums. Looks like a needed FAQ entry.

Yes. The flow could be calculated at the end of the pipe. Probably should be done both ways.

May a better way to measure the air flow is to isolate the line. Hook up an air cylinder to it. Note the beginning and end pressure (time with a stop watch) and calculate the flow.

 

[TD2K]

http://www.cranevalve.com/tech.htm

 

[3243]

how do i find the velocity at any point depending on the diameter of the pipe, what is the equation that i need to find mean velocity of the air at any point in the pipe depending on the diameter???
thanks for your help

 

[rbcoulter]

You must first calculate the flowrate via the equation (or equivalent) mentioned above before calculating the velocity. This is air at a constant temp so the density of the air will vary with pressure. The mass flow is constant at any point in the pipe. The mean velocity at a point in the pipe is the mass flow divided by the density, divided by the cross-sectional area of the pipe at that point.

 

[TD2K]

3243, you are way out of your depth on this work based on your questions.

Why are you doing this? What is the answer for? Is there no one qualified/experienced there you can talk to? If you don't understand this, you can very easily get a totally wrong answer and won't know it. Trying to learn fluid flow on this forum is likely just going to get you more confused.

 

[3243]

Thanks for all your help,