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CHAPTER 3
Fluid Friction in Pipes

In Chemical engineering process operations , fluids are
typically conveyed through pipelines, in which viscous
action.
 Such friction is normally overcome either by means of
the pressure generated by a pump or by the fluid falling
under gravity from a higher to a lower elevation.
 In both cases it is necessary to know what flow rate
or velocity can be expected for given driving force.
 For a given flow rate, repetition of the experimental for
different lengths demonstrates that the pressure drop(
P1-P2) IS DIRECTLY PROPORTIONAL to L.
 There are three different flow regimes in the resulting
graph:



For flow rates that are low, the pressure gradient is directly proportional to
the flow rate( LAMINAR).
For intermediate flow rate, the results are irreproducible, and alternate
randomly between extension of regimes 1 and 3( TRANSITION )
For the high flow rate, the pressure gradient is closely proportional to square
of the flow rate( TURBULENT )
3.2 Laminar Flow
 In
laminar flow the fluid is moving at low
flow rate. In order to avoid additional
complication of gravity, consider flow in
horizintal cylinder pipe of radius a as
shown in figure below. Consider a fluid
moving in cylinder with radius r and length
L. because of the retarding action of the
pipe wall, there will be shear stress 
between the fluid and pipe wall