Page 90 - Mechanical Engineers' Handbook (Volume 4)

11 Viscous Fluid Flow in Ducts 79

Table 8 Friction Factors for Laminar Flow

1
2 log(Re ƒ) 0.8
D
ƒ
which agrees well with experimental values. A more explicit formula by Colebrook is
1/ ƒ 1.8 log(Re /6.9), which is within 1% of the Prandtl equation over the entire range
D
of turbulent Reynolds numbers.
The logarithmic velocity defect profiles apply for rough pipes as well as for smooth
pipes, since the velocity defect (u max u) decreases linearly with the shear velocity v ,