LAMINAR AND TURBULENT FLOW
Fluid Flow
where:
NR = Reynolds number (unitless)
v
= average velocity (ft/sec)
D
= diameter of pipe (ft)
µ
= absolute viscosity of fluid (lbf-sec/ft2)
r
= fluid mass density (lbm/ft3)
gc
= gravitational constant (32.2 ft-lbm/lbf-sec2)
For practical purposes, if the Reynolds number is less than 2000, the flow is laminar. If it is
greater than 3500, the flow is turbulent. Flows with Reynolds numbers between 2000 and 3500
are sometimes referred to as transitional flows. Most fluid systems in nuclear facilities operate
with turbulent flow. Reynolds numbers can be conveniently determined using a Moody Chart;
an example of which is shown in Appendix B. Additional detail on the use of the Moody Chart
is provided in subsequent text.
Summary
The main points of this chapter are summarized below.
Laminar and Turbulent Flow Summary
• Laminar Flow
Layers of water flow over one another at different speeds with virtually no
mixing between layers.
The flow velocity profile for laminar flow in circular pipes is parabolic in shape,
with a maximum flow in the center of the pipe and a minimum flow at the pipe
walls.
The average flow velocity is approximately one half of the maximum velocity.
• Turbulent Flow
The flow is characterized by the irregular movement of particles of the fluid.
The flow velocity profile for turbulent flow is fairly flat across the center section
of a pipe and drops rapidly extremely close to the walls.
The average flow velocity is approximately equal to the velocity at the center of
the pipe.
• Viscosity is the fluid property that measures the resistance of the fluid to deforming
due to a shear force.
For most fluids, temperature and viscosity are inversely
proportional.
• An ideal fluid is one that is incompressible and has no viscosity.
• An increasing Reynolds number indicates an increasing turbulence of flow.
HT-03
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