Fluid Friction in Pipes

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Fluid Friction in Pipes

• CHAPTER 3

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• 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

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• 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 )

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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

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