where Vavg 5 average flow velocity (m/s), D 5 characteristic length of the
geometry (diameter in this case, in m), and n 5 m/r 5 kinematic viscosity
of the fluid (m2
/s). Note that the Reynolds number is a dimensionless quantity
(Chap. 7). Also, kinematic viscosity has the unit m2
/s, and can be
viewed as viscous diffusivity or diffusivity for momentum.