Chemical Engineering - Chemical Engineering Basics - Discussion

F depends upon Re and Re doesn't depend upon length and roughness depend upon dia only so A.

But as we know h = 4flv2/2gd.

Hi Guys.
Greetings.

As far as the friction factor is concerned it is true that the friction factor is independent of length, why ?

The answer is f is a dimensionless number and is a ratio of the shear stress at the wall of a conduit to the kinetic energy or velocity head of the flow, and thus you will not find any dependence of f(friction factor) on length.

Hope this answers your question.

If we keep eyes on formula there is length in it. So how can you say that it does not depend on length.

@A.K.

The formula is hf = 4fLv2/2gD.

Which is made to find out the friction loss in the pipe, so the friction loss hf (frictional head) is dependent on length (how long we want to pump a fluid).

To find out friction factor value we prefer Analogies (Reynold or Colburn Analogy etc) which are fully based on dimensionless numbers(Prandtl and Stanton number) in those numbers you will never find any length factor.

On this basis I'm claiming the friction factor is independent of length.

Hope this answers your question.

Re = flv2/2gD.

From above relation we can conclude that friction factor depend upon length of pipe. But f is independent of mass flow rate a/c to me.

Pressure drop due to frictional loss is (4fLv^2)/(2gD). Where f is the fanning friction factor. And that is dependent on Reynolds number which is Dv*rho/mu.

Question asked is related to frictional factor and not pressure drop die to frictional losses.

Due*
Frictional*

Hence frictional factor is not dependent on length.

@Muhammad.

Very well done, Thanks.

f = 16\ Re.
-> Re = Dvd\vicosity.