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# Formula For Maximum Flow Through Pipe

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3 replies to this topic
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### #1 Guest_FrankSchleck_*

Guest_FrankSchleck_*
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Posted 07 August 2008 - 08:32 AM

Dear,

I'm trying to check maximum flowrate through a pipe and got the following parameters:

pipe, DN-25
P1 = 60 barg
P2 = 46,3 barg
medium, natural gas at 25°C, ie. density at 60 barg = 43,5 kg/m³

I used the formula out of PRENSAP B6.1.2:

W = (rho*Di^5*(P1-P2)/0,81*lambda*L)^0,5

How come I always come up with the same average velocity in m/s, regardsless which Di I choose?

Agnes

### #2 Art Montemayor

Art Montemayor

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Posted 07 August 2008 - 09:17 AM

Agnes:

I don't know what "PRENSAP B6.1.2" is, but I do know that in order to find the flow rate of a compressible fluid through a circular pipe, you have to establish:

the pipe diameter;
the driving force (pressure drop);
the pipe length;
the fluid properties (viscosity, density, temperature);
the number and type of fittings and valves - and all other resistances;
the friction factor.

Your question involving the velocity is vague and doesn't tell us what equation or method you are obviously using wrongly. We can't answer your question if you don't tell us what relationship or tools you are using to come up with the wrong answer(s). Your answers are wrong because the average fluid velocity is going to definitely going to change with the diameter varying.

We can't give you an answer based on what information you furnish.

Additionally, just specifically what is your query? Is it the formula for the max flow rate? Or is it the velocity question? --Or both?

### #3 ankur2061

ankur2061

Gold Member

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• 2,484 posts

Posted 07 August 2008 - 10:02 AM

Hi Agnes,

I am putting an attachment on compressible flow through pipelines. It is a very informative article on compressible flow covering the various equations such as AGA, Weymouth, Panhandle A & B etc.

Maybe some of the young engineers who are whiz kids in writing "Visual Basic" programs in excel can utilize this article to prepare a spreadsheet and share it with the forum readers.

Regards,
Ankur.

### #4 CMA010

CMA010

Gold Member

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• 92 posts

Posted 07 August 2008 - 12:04 PM

The PRENSAP formula you used is for liquids. It's the same formula from DEP 31.38.01.11 (formula 3a). In the DEP it says you can't use it for compressible flow. If you want to calculate the maximum flow through the pipe for a number of diameters i suggest you use Crane Technical Paper 410M (equation 3-20 and page A-22).