Pipeline Flow - FDTF

[Stuuus]

Good Evening,

I am currently creating a new calculation spreadsheet, part of this is a back pressure calculator which shows the type of flow using the churchill friction factor, this is shown graphically on a moody diagram as per the below image. However, I have multiple pipeline sections with multiple fluids available, so am trying to get excel to output the type of flow (eg. laminar, transitional, turbulent and FDTF). I cannot however figure out how to get excel to automatically determine this, without needing dozens of moody diagrams and the engineer to visually check these each time. Even if I can get the FDTF line to plot and then get excel to determine if the result is above this line. However, thus far I have had no luck.

Any assistance appreciated.

 

[gwalkerb]

I ran into this same challenge, and never did come up with a solution that didn't involve manually reading off of a Moody diagram. However, I did come across this page when searching,

http://radiganengineering.com/2013/07/friction-factor-calculation-in-excel/

, which has a reference back to this very website.

http://www.eng-tips.com/faqs.cfm?fid=1237

This might give you some more ideas to move forward. I'll probably go back to my own sheets and see if I can use these formulas as well.

 

[Stuuus]

Thanks for that. That's how I have currently got it, as in the above image. the curve is produced using the Churchill correlation (as per the radigan link) and then the Re is plotted as a vertical line at the appropriate location. However, without looking back at the diagram each time.

Do you know if there is a formula for the curve representing the FDTF boundary?

Another way I have tried is by using various friction factor equations which claim to only work for one flow regime, then comparing the churchill value to these values, however I have not been able to get it to give the correct flow type with any reasonable repeatability.

 

[Stuuus]

Having a think just now and as the complete turbulence region f is independent of Re, I'll try doubling the Re and if the resulting f is closely approximate to the original value of f, then the flow is completely turbulent. Will give it a go and let you know how I get on.


EDIT:

Rounding to 3 decimal places, with double Re, seems to work well apart from at the boundary region, where it isn't overly accurate, better than any results i've achieved to date however.

 

[Stuuus]

Result.

Have now got it to determine if FDTF or Laminar. Couldn't get transitional so am counting transitional as everything not Laminar or FDTF. For anyone interested, code below:

Re = cell C34
2Re = cell C53
f - original - cell C57
f - 2Re = cell C56

Churchill A =POWER(-2.457*LN((POWER((7/C53),0.9)+(0.27*(B20)))),16)
Churchill B =(37530/C53)^16
f - 2Re =8*((8/C53)^12+(C54+C55)^(-1.5))^(1/12)
FDTF True/False =IF(ROUNDUP(C56,3)=ROUNDUP(C57,3),TRUE,FALSE)

f - laminar = =64/C34
Laminar True/False =IF(ROUNDUP(C60,3)=ROUNDUP(C57,3),TRUE,FALSE)

 

[katmar]

A comment on your terminology - some authors do refer to the zone between Reynolds Numbers of 2000 and 3000 as the Transition Region but I prefer to use the Crane TP410 terminology and call this the Critical Zone. Crane uses the Transition Zone terminology for the zone above an Re of 3000 but below the fully developed turbulent flow zone. This helps to highlight the fact that the zone between Re of 2000 and 3000 should be a no-go zone.

One way of identifying whether you are in the FDTF zone would be to calculate the friction factor using the Churchill equation and also with the von Karman equation i.e. f = 1/(2 x log[sub]10[/sub](3.7/(e/d)))[sup]2[/sup]

If the Churchill and von Karman values are "sufficiently close" then you are in the FDTF zone.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[Stuuus]

Perfect. thanks alot.