10 replies to this topic

[huigrant]

Can someone describe when to use a Moody friction factor chart and when to use a Fanning chart?

[breizh]

this resource should support your query :

http://www.pipeflow....ach_Formula.pdf

Hope this helps

Breizh

[Zauberberg]

You use whichever you want, as long as you know to which equation they apply. Their relationship is always the same, i.e. f(D) = 4*f(F)

D = D'Arcy
F = Fanning

[breizh]

A spreadsheet to calculate the Friction factor (Darcy or Moody) for turbulent flow .

Breizh

[Art Montemayor]

Huigrant:

I consider this a very important question in Fluid Mechanics because, although it is a very simple and basic one, it is often the cause of much confusion and mistakes in calculating the pressure drop of fluids. I have discovered through the years that some engineers don’t even know that there are basically TWO friction factors in this world – and one of them is FOUR TIMES the other.

You use the Moody (actually, the Darcy) friction factor when using the Darcy equation for pressure drop. You use the Fanning friction factor when employing the Fanning equation for pressure drop. The Darcy friction factor is 4x the value of the Fanning friction factor – so DON’T MIX THEM UP.

For details of what I write, go to: http://en.wikipedia....iki/Moody_chart

I am at a loss as to why chemical engineering university courses and textbooks still persist in teaching and using the Fanning equation. It clearly is the least used in actual engineering design, where the Darcy is much more popular and widely used. But you must be specific as to which equation and which factor you employ. I have seen the two relationships mixed up far too many times in the past and this is a constant problem and something to always be wary of.

[katmar]

There is a third version of the friction factor, which is rarely used in the USA and non-English speaking countries. It was/is used as the basis of the development of the Darcy-Weisbach equation in Volume 1 of the series "Chemical Engineering" by Coulson and Richardson. These authors were from the Universities of Newcastle and Swansea in the UK and the series was (and still is) very widely used there, as well as in South Africa and Australia. They always pointed out the relationship to the Fanning friction factor, and in the more recent editions the Moody friction factor as well. C&R's friction factor, which I have called the Stanton friction factor in my Uconeer units conversion program, is 1/2 of the Fanning factor and 1/8 of the Moody factor.

[huigrant]

Thanks for all of the responses!

[breizh]

Hi ,
an update on f calculation
Hope this helps
Breizh

[Art Montemayor]

Breizh:

Thank you very much for the contribution.

But in keeping with Katmar's valuable information regarding the various versions of the Friction Factor, which version does this workbook calculate - the Fanning, Darcy (Moody), or the Stanton?

[breizh]

Hi Art ,
Hope this version will provide a better support .
It's refer to the Darcy factor
Breizh

[Bayo Alabi]

There is a good website that explains the calculation steps and applications of both Fanning and Darcy (Moody) friction factor.

1. Go to http://www.processca...tion_factor.jsp for calculation steps
2. Go to http://www.processca...ifferential.jsp for applications of the friction factor.