pipe minor loss coefficient 2

[ceseng]

when you guys do pressure pipe model, do you predefine the pipe minor loss coefficient?

I always use 1.5, no matter what pipe size, length. Today, when I read a report prepared by another engineering firm, they put 0.

what is you guys' suggestion?

 

[RWF7437]

From the EPANet2 Help file:

"Minor Loss Coefficients

Globe valve, fully open 10.0
Angle valve, fully open 5.0
Swing check valve, fully open 2.5
Gate valve, fully open 0.2
Short-radius elbow 0.9
Medium-radius elbow 0.8
Long-radius elbow 0.6
45 degree elbow 0.4
Closed return bend 2.2
Standard tee - flow through run 0.6
Standard tee - flow through branch 1.8
Square entrance 0.5
Exit 1.0 "

Just one guyses suggestion .

 

[katmar]

If you are applying a single number, then it sounds like what you using is what is usually called a "complexity factor". It is simply a fudge factor (safety factor) that is used to multiply the length of straight pipe by to make allowance for elbows, valves etc. It will vary very much from installation to installation and it is hard to give a universally acceptable number.

I prefer to use the approach suggested by RWF7437 and include the losses for the actual fittings unless it is a very preliminary calculation and the details of the fittings are unknown - in which case I would agree with your 1.5 factor. And then when you have the details of the fittings you can revisit the calc and confirm the pressure drop.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Artisi]

Fudge factor, this is why many pumps end up oversized for the application especially after everyone involved adds their own "fudge factor".
Calculate it or make a sound engineering assumption even if it is a very preliminary estimate.

 

[RWF7437]

http://books.google.com/books?id=pHVDDo6RtEMC&pg=PA262&lpg=PA262&dq=when+to+ignore+minor+los

 

[BigInch]

That's only 0.2% of total head loss. Given that margins of error in hydraulics are usually (well) more than 5%, that's really a pretty low threshold.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[tkall]

The question is.....how close is close enough? I was not satisfied with the tabulated values I have seen published so I conducted my own study with surprising results. For instance, when I measured the minor loss coefficient through a 90 degree elbow discharging freely, the number agreed exactly with published data. However, when I added some pipe to the discharge side of the elbow the minor loss coefficient jumped dramatically. Furthermore, minor loss coefficients are a function of pipe diameter as well. In a system dominated by minor losses, it makes sense to know rather than guess...or even worse to hope that the person providing the data knows what they are talking about.
Tom
info@squirtonsite.com

 

[Artisi]

tkall, a very valid point - "In a system dominated by minor losses, it makes sense to know rather than guess.........." .

The main reason for my earlier post, re adding fudge factors. A minor loss dominated system would have a much different answer than a system with only a couple of minor losses - adding a "standard" fudge factor is a guess.
Calculate don't guess.