The volume flow rate of an incompressible fluid in a round pipe is given by:
Q = volume flow rate [m3s-1]
r = radius of pipe [m]
p1-p2 = pressure difference between points 1 and 2 [Nm-2]
μ = dynamic viscosity of fluid [Nsm-2]
L = distance between points 1 and 2 [m]
The velocity profile across the cylinder is seen to be parabolic, and this relation affords a convenient experimental means of determining a fluid′s viscosity.