Fanning Friction Factor

The Fanning friction factor, named after John Thomas Fanning (1837–1911), is a dimensionless number used in fluid flow calculations. It is related to the shear stress at the wall as:

\tau = \frac{ f \rho v^2}{2}

where:

  • is the shear stress at the wall
  • is the Fanning friction factor of the pipe
  • is the fluid velocity in the pipe
  • is the density of the fluid

The wall shear stress can, in turn, be related to the pressure loss by multiplying the wall shear stress by the wall area ( for a pipe) and dividing by the cross-sectional flow area ( for a pipe).

The friction head can be related to the pressure loss due to friction by dividing the pressure loss by the product of the acceleration due to gravity and the density of the fluid. Accordingly, the relationship between the friction head and the Fanning friction factor is:

h_f = \frac{ 2fv^2L}{gD}

where:

  • is the friction loss (in head) of the pipe.
  • is the Fanning friction factor of the pipe.
  • is the fluid velocity in the pipe.
  • is the length of pipe.
  • is the local acceleration of gravity.
  • is the pipe diameter.

Read more about Fanning Friction Factor:  Fanning Friction Factor Formulæ

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