Friction in Pipelines (as headloss)

[Mikealvarado100]

When we talk about headloss in pipelines (which is defined with Darcy-Weisbach or manning or hazen-Williams equations) we talk about friction between liquid and pipe wall and we do not talk about moving molecules of water on each other. Does not it (moving liquid surfaces on each other)result friction in fluid as headloss? This phenomenon can affect both on headloss in steady state condition and transient condition.
Would anyone explain about?

Thanx in advance.

 

[boneh3ad]

What you are essential describing is viscosity, and yes, it is the primary contributor to head loss. It honestly annoys me that so many texts talk about "friction" because it isn't friction in the traditional sense, but viscous losses are similar enough to frictional losses that this has become common terminology.

 

[billslugg]

The component of viscosity induced head losses due to wall friction is zero. The layer of fluid touching the wall is at zero velocity. There is no wall friction. All losses are caused by shear in the fluid. What wall roughness does is generate eddies in the fluid thus increasing the work needed.