Water Flow in Tubes - Reynolds Number

Reynolds Number in pipes transporting clean cold water

Turbulent or laminar flow is determined by the dimensionless Reynolds Number.

The Reynolds number is important in analyzing any type of flow when there is substantial velocity gradient (i.e., shear.) It indicates the relative significance of the viscous effect compared to the inertia effect. The Reynolds number is proportional to inertial force divided by viscous force.

The flow is

  • laminar when Re < 2300
  • transient when 2300 < Re < 4000
  • turbulent when 4000 < Re

The table below shows Reynolds Number for one liter of water at aprox. 20oC (68oF) flowing through pipes of different dimensions:

Pipe Size
(inches) 1 1 1/2 2 3 4 6 8 10 12 18
(mm) 25 40 50 75 100 150 200 250 300 450
Reynolds number with
one (1) liter/min
835 550 420 280 210 140 105 85 70 46
Reynolds number with
one (1) gal/min
3180 2090 1600 1060 780 570 400 320 265 175

Note that viscosity of water varies with temperature.

  • the kinematic visosity of water at 20oC - used to calculate the table above - is 1.004·10-6 m2/s
  • at 0oC the kinematic viscosity is 1.787·10-6 m2/s - the Reynolds values in the table above must be multiplicated with 1.004 / 1.787 = 0.56
  • at 100oC the kinematic viscosity is 0.29·10-6 m2/s - the values in the table above must be multiplicated with 1.004 / 0.29 = 3.46

Related Topics

  • Fluid Mechanics - The study of fluids - liquids and gases. Involves various properties of the fluid, such as velocity, pressure, density and temperature, as functions of space and time.
  • Fluid Flow and Pressure Drop - Pipe lines - fluid flow and pressure loss - water, sewer, steel pipes, pvc pipes, copper tubes and more

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