Friction loss is the loss of energy or "head" that occurs in pipe flow due to viscous effects generated by the surface of the pipe.

Friction loss is considered as a "major loss" and it is not to be confused with "minor loss" which includes energy lost due to obstructions.

Friction loss has several causes, including:

  • Frictional losses depend on the conditions of flow and the physical properties of the system.
  • Movement of fluid molecules against each other
  • Movement of fluid molecules against the inside surface of a pipe or the like, particularly if the inside surface is rough, textured, or otherwise not smooth
  • Bends, kinks, and other sharp turns in hose or piping
  • In pipe flows the losses due to friction are of two kinds: skin-friction and form-friction. The former is due to the roughness of the inner part of the pipe where the fluid comes in contact with the pipe material, while the latter is due to obstructions present in the line of flow--perhaps a bend, control valve, or anything that changes the course of motion of the flowing fluid.

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