Accuracy of calculation of pressure loss in pipes ??

[Yobbo]

Dear reader,
I make my pressure loss calculations with the Darcy Weisbach formula and The Colebrook formula. I get THE impression though that when it comes to using à dzeta value for valves, bends, filters asf. The accuracy is very limited. I have looked for information about THE accuracy of these kind of calculations, but I can't find anything. I Hope that in this forum there Will be someone able to enlighten me about this. I think it is an important subject, because sizing à system of pipelines and pumps requires knowledge about this.

Karel Postulart, The Netherlands
Nuon Power Generation

 

[zdas04]

"Pressure loss calculations" in what fluid? What Reynolds Numbers?

Each of the equations you mention have a number of assumptions built into them. If your conditions are exactly the same as the assumed conditions then your calculated pressure drop will be about as good as gauge accuracy (e.g., if you have a +/-5% 0-10,000 psig gauge then your uncertainty in measurement is +/-500 psig, so any dP less than 500 psig calculated by your equation would be meaningless). If you have a +/-0.5% device with a full scale of 0-50 psig, then you have an uncertainty in measurement of +/-0.25 psig. Taking that kind of data into Darcy can probably give you around +/- 5-10% uncertainty if all the other assumptions are satisfied.

If the assumptions are not satisfied then the arithmetic is garbage. Darcy Weisbach assumes constant density, constant flow with time, and turbulent flow.

David

 

[21121956]

Hello everybody:

Take a look to this thread378-173164, there you can find a very good approach to this subject.