Civil Engineering Reference
In-Depth Information
the tank, usually with entrance velocities less than 2 ft / sec (0.6 m / s), distributing the
flow across the full width of the tank. A perforated baffle wall located across the tank
can provide excellent flow distribution (Fig. 11-4). The best location for such a baffle
has been reported to be 6.5 to 8 ft (2 to 2.5 m) downstream of the basin inlet wall.
10
In the design of perforated baffles, Hudson states that four requirements must be
met:
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The headloss through the ports should be about four times higher than the kinetic
energy of any approaching velocities in order to equalize flow distribution both
horizontally and vertically.
•
To avoid breaking up floc, the velocity gradient through inlet conduits and ports
should be held down to a value close to or a little higher than that in the last
compartment of the flocculators.
•
The maximum feasible number of ports should be provided in order to minimize
the length of the turbulent entry zone produced by the diffusion of the submerged
jets from the ports in the perforated-baffle inlet.
•
The port configuration should be such as to ensure that the discharge jets will
direct the flow toward the basin outlet.
•
It is desirable for the port diameter to be no more than the thickness of the per-
meable-baffle wall, so that the hydraulic behavior will cause the jets to emerge in the
proper direction. Hudson presents a design procedure for determining the size and
spacing of the ports. He reports that it is safe to use a velocity through the perforated
baffles of about 0.65 to 1 ft / sec (0.2 to 0.3 m / s).
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Uniformly distributed 5-in. (0.13-
B
Baffle Wall
B
Plan View
Section B
Fig. 11-4.
Perforated inlet baffle wall (From Culp, Gordon, and Williams, Robert,
Handbook of
Public Water Systems.
Copyright
1986 by John Wiley & Sons, Inc. Reprinted by permission
of John Wiley & Sons, Inc.)
