The Darcy-Weisbach formula is intended to calculate the linear pressure drop. In a cylindrical pipe of uniform diameter D, flowing full, the pressure loss due to viscous effects Δp is proportional to length L.

Regards

Linear equation but; If the storage head is variable (i.e. during emptying), then the flow will be "Unsteady", and the losses will be exponentially propotional to "V^2" with a curve trend.

The main assumption in the Darcy friction factor is that flow is laminar. You should calculate the Reynolds number (Re= rho*velocity*diameter/mu) for the pipe size based on the operating flow rate to make sure the flow is laminar (i.e., Re

Dear Pat Quinn,

I don't agree with you at all. The Colebrook-White relation which expresses the coefficient of friction as a function of the relative roughness and the Reynolds number is valid in the whole field of turbulent flow (i.e. smooth, transition, and rough) Re greater than 2300 (See Moody diagram). It has nothing to do with the laminar regime. The Darcy-Weisbach friction factor for laminar flow is calculated by dividing 64 by Reynold's number (Poiseuille's law). The Darcy – Weisbach equation is an empirical equation, which relates the head loss, or pressure loss, due to friction along a given length of pipe to the average velocity of the fluid flow for an incompressible fluid, whatever the flow regime (There is no assumption on the flow regime). The coefficient of friction, noted f and contained in the Darcy-Weisbach relationship, is calculated by the Colebrook-White relation if the regime is turbulent (i.e. Re greater than 2300) or by the Poiseuille relation f = 64 / Re if Re is less than 2300.

Regards

Bachir, I don't disagree with your methodology, however, in your first answer you say the equation is intended for linear losses, which is the way I look at it. Therefore I suggested they check that the losses are linear with Re if they use the Darcy-Weisbach solution for linear losses. No one said anything about using Colebrook except you.

Bachir Achour and Pat Quinn thank you so much but dear Bachir Achour i know how calculate friction loss with for the deffirents cases of darcy factor. I have found that darcy's equation allows it to calculate major friction losses. but it is necessary to add the minor friction as "elbow valve ...." we can say that the minor friction are the singular friction losses.

Dear Par Quinn,

Colebrook's Formula bas been cited thousands of times in the literature. It is still cited today. So you can check that I'm not the only one talking about it. That would be pretentious.

Regards

@Bachir. Ok thank you dear