2

The ßow in a pipe may be either laminar or turbulent, depending on the Reynolds number,

¬

, and the amount of perturbation. The Reynolds number is deÞned as

(2.2)

where

r

is the density of the ßuid;

m

is the dynamic viscosity;

n

is the kinematic viscosity;

V

is the cross-sectional mean velocity of the ßow in the pipe; and

D

is the inner diameter of the pipe.