text: Early approximations for smooth pipes by Paul Richard Heinrich Blasius in terms of the Darcy–Weisbach friction factor are given in one article of 1913:
  Johann Nikuradse in 1932 proposed that this corresponds to a power law correlation for the fluid velocity profile.
  Mishra and Gupta in 1979 proposed a correction for curved or helically coiled tubes, taking into account the equivalent curve radius, R:
  with,
  where f is a function of:
  * Pipe diameter, D (m, ft)
  * Curve radius, R (m, ft)
  * Helicoidal pitch, H (m, ft)
  * Reynolds number, Re (dimensionless)
  valid for:
  * Re 
  * 6.7 /D < 346.0
  * 0 < H/D < 25.4