# Von Karman and Prandtl laws

1. Apr 26, 2016

### foo9008

1. The problem statement, all variables and given/known data
there are 2 formula of vont karman and prandit laws to find the friction factorfor rough pipe and smooth pipe , which formula should i use for this question?

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P/ s : I'm asked to find the friction factor using the vont karman and prandit laws.
2. Relevant equations

3. The attempt at a solution

2. Apr 26, 2016

### foo9008

it didnt stated whether it's smooth or rough pipe , which formula should we use?

3. Apr 26, 2016

### BvU

I was going to propose you do both (assuming some reasonable $e$ for galvanized ion pipe ) and compare ...

On the other hand, you do have the data to calculate Re so I certainly wouldn't leave out that one...

4. Apr 27, 2016

### foo9008

well , i have found that the f for rough pipe is 0.017 , nut i am not sure how to find f for smooth pipe using von karman and Prandlt laws ... for smooth pipe , i have 1 / ( surd f ) = 2 log [(3.72 x 10^5) (surd f ) / 2.51 ]

P/ s: by using scientific calculator , i get the f for smooth pipe is 0.014 , which value should i choose ? f= 0.017 or 0.014 ?

5. Apr 27, 2016

### Nidum

Edit : Duplicate information removed .

Last edited: Apr 27, 2016
6. Apr 27, 2016

### foo9008

so , do you have any comment on this question / which is correct ?