calculation of friction losses
calculation of friction losses
(OP)
I am studying electrical engineering and work on a project regarding solar water pumping. To dimension the pump and the solar array I need to calculate the total head (of existing pipe grids).
I have to calculate the pipe friction losses and I'm searching for a suitable equation. For laminar condition I use following equation to calculate the friction factor: f = 64/RE.
As I have no experience on this field there are some questions:
How important is the roughness factor of the pipe for the friction losses in turbulent flow conditions? Is it negligible?
Which effects have the different roughness factors on the total head? Can I use one general roughness factor for all used materials (piping for village water supply, livestock watering and irrigation)?
I'm grateful for every hind I get!
What are suitable equations for practical calculations?
I have to calculate the pipe friction losses and I'm searching for a suitable equation. For laminar condition I use following equation to calculate the friction factor: f = 64/RE.
As I have no experience on this field there are some questions:
How important is the roughness factor of the pipe for the friction losses in turbulent flow conditions? Is it negligible?
Which effects have the different roughness factors on the total head? Can I use one general roughness factor for all used materials (piping for village water supply, livestock watering and irrigation)?
I'm grateful for every hind I get!
What are suitable equations for practical calculations?





RE: calculation of friction losses
Head loss = f(l/d)/(v^2/2g)
f is determined from a chart relating loss to roughness and Reynolds number. I can scan and Email you a copy if you wish.
However, for most cases f = .02 will serve nicely.
"Minor losses" from elbows, tees, valves, etc wil frequently completely overshadow the pipe friction loss.
RE: calculation of friction losses
Regards
http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm#calc
http://www.mainind.com/design/
http://www.monachos.gr/greek/calculators/Darcy_weisbach.htm
http://www.geocities.com/Eureka/Concourse/3075/hazen2.html
http://www.freecalc.com/fricdia.htm
http://www.freecalc.com/fricfram.htm
RE: calculation of friction losses
Other than that, stick with Insideman's formula.
RE: calculation of friction losses
But there is still a problem: the calculation is part of a computer-program.
This program should help non-experts (like farmers) to develop there own PV water pumping system. It includes the calculation and a simulation-part. Therefore I can't use the chart to obtain the friction factor. I have to choose an average factor or calculate it in "real-time". Also there is no constant flow due to the power supplied by pv-modules.
My predecessor has suggested to use the Blasius equation for RE > 2316:
f = 0.316/RE^0.25
in books this equation is said to be accurate for smooth pipes and RE between 5000 and 10^5.
Using this equation for RE near to 2316, I calculated a friction factor of 0.045. That's double of the value you suggested.
So I don't know if I can use this equation. What do you think?
Does anyone know another way to determine f?
RE: calculation of friction losses
RE: calculation of friction losses
If you don't want to go through an interative solution, there are several approximations that will yield acceptable results over a specific range of Reynold's number. One recommendation is:
http://sellensr.me.queensu.ca/sellens/441/losses.htm
I used to have several papers that discussed various correlations and their accuracy, I'll have to see if I can dig them out from my files at home.
RE: calculation of friction losses
Sorry, usually my filing system doesn't work so well. This was from an article in Chemical Engineering magazine (the date didn't copy unfortunately).
The equation unfortunately is a little ugly to try and enter here:
I'll scan it and it can be downloaded from:
http://briefcase.yahoo.com/testdog2000
RE: calculation of friction losses
The input variables I think speak for themselves.
Maybe they could be of use to you?
Dim FrictionFactor As Variant
Dim Testvalue As Variant
Dim Stopvalue As Variant
Dim MediumVelocityTest As Variant
Dim ReynoldsNumber As Variant
Public Function ReynoldsNo(PipeID, MediumVelocity, MediumDensity, Viscosity_dyn)
ReynoldsNo = MediumVelocity * PipeID * MediumDensity / Viscosity_dyn
End Function
Public Function FrictionFactorMoody(PipeID, RoughnessFactor, ReynoldsNumber)
If ReynoldsNumber < 2000 Then
FrictionFactor = 64 / ReynoldsNumber
Else
FrictionFactor = 0.12
counter = 0
Do
Testvalue = FrictionFactor
FrictionFactor = 1 / (-2 * (1 / Log(10)) * Log((RoughnessFactor / (3.7 * PipeID)) + 2.51 / (ReynoldsNumber * (Testvalue) ^ 0.5))) ^ 2
Stopvalue = Abs(Testvalue - FrictionFactor)
counter = counter + 1
Loop Until Stopvalue < 0.000001
End If
FrictionFactorMoody = FrictionFactor
End Function
Regards
Mogens
RE: calculation of friction losses
I thought I was the only one that read technical papers at night... My wife thinks I'm crazy...
Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com
RE: calculation of friction losses
The article you sent me was very helpful!!
I think I use the most ugly equation (equation (2)). This means only 4 lines of code.
Now I need the roughness of the different pipe-materials. (Especially for plastic-pipes)
The books I found in the library contain no tables.
Does anybody now links or other sources for this information?
Also would be great to get the loss coefficients for fittings valves etc..
I found some tables but they all show different values.
Again thanks allot for your help!!
RE: calculation of friction losses
RE: calculation of friction losses
I would take plastic pipe somewhere between clean commercial steam pipe (e = 0.00015 ft) and tubing (e = 0.000005 ft) where e is the absolute roughness but a lot of it depends on how clean your water is, treatment, etc because fouling or deposits in the pipe will increase the effective roughness and decrease the diameter (and changes in the diameter affect the pressure loss proportional to the 5th power, that is,
d1/d2 is proportional to (dP1/dP2)^5.
RE: calculation of friction losses
RE: calculation of friction losses
RE: calculation of friction losses
I opened your briefcase and found valuable stuff inside
I appreciate very much of your efforts.
Regards,
RE: calculation of friction losses
May be good books on hydrailics have roughness of materials, but all these books seam to be on loan. Again I tried to find some in the library and found (after a long search) one book. It has a short table with roughness of some materials.
There is only one value for glass and plastic together. It is 0.0008 in..
It has no value for aluminum.
If you have a more detailed table, please let me know.
I'm very grateful for your help!!