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Entrance
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Tank
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Design
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Program
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The
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purpose
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of
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this
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program
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is
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to
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design
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the
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dimensions
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of
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the
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entrance
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tank
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based
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on
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the
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flow
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rate
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of
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the
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plant
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and
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the
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head
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loss
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required
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for
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rapid
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mixing.
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The
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Entrance
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Tank
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is
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constructed
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as
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a
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separate
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channel
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before
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the
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flocculator
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and
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in
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current
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schematics
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is
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located
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offset
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with
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the
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chemical
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storage
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tanks
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a
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distance
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from
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the
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flocculator
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enough
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to
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provide
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a
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walkway.
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A view of just the tank, without the rapid mix system. The thickness of tank wall is T.PlantWall.
The entire entrance tank, with rapid mix system is shown below. The macro-mix orifice is the cap on top, while the orifices, pipes, and elbows account for a head loss that will provide a total head loss of 40 cm (HL.PlantTotal, an Expert Input) throughout the plant.
Entrance Tank Design Program Algorithm
Entrance Tank Program Inputs
Entrance Tank Program Outputs
Entrance Tank AutoCAD Drawing Program
Algorithm
The entrance tank is designed to be a separate channel before the flocculator to house the rapid mix system and provide the head necessary to drive water through the plant.
The area of the entrance tank is calculated based on the flow rate through the plant and the required up-velocity through the entrance tank (found in Design Assumptions).
| Include Page | ||||
|---|---|---|---|---|
|
The water level in the entrance tank is designed to meet requirements for rapid mix, as well as head loss due to flow from the entrance tank to the flocculator. These variables can be found in the Rapid Mix, Flocculation, Sedimentation Inlet Slopes, and User Inputs design programs.
| Latex |
|---|
\large
$$
HW_{EtTotal} = HW_{EtMax} + HL_{FlocEntryOrifice} + HL_{Floc} + HW_{Sed} + HW_{EtWaterFall} + HW_{EtChannel}
$$
|
...
| Latex |
|---|
\large
$$
HW_{EtMax} = HW_{EtMin} + HL_{Lfom}
|
...
$$ |
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The
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height
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of
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the
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entrance
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channel
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is
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based
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on
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the
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elevation
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of
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the
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tank
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and
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providing
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a
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distance
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of
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two
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pipe
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diameters
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beneath
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the
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tank,
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along
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with
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room
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for
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a
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pipe
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radius
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and
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thickness
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of
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concrete.
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The
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tank's
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base
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does
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not
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need
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to
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extend
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to
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the
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base
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of
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the
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flocculator.
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Because
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it
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can
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be
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elevated,
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the
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flocculator
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can
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be
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dug
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into
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the
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ground
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and
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less
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concrete
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needs
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to
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be
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poured.
| Latex |
|---|
} \large $$ H_{Et} = Z_{Et} - H_{Sed} - H_{InletChannel} + H_{SedWeirExit} + 2*ND_{RMPipe} $$ {latex} !tankelevation.png|width=414,height=380! The length of the entrance tank |
The length of the entrance tank (L.Et)
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is
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the
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square
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root
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of
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the
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entrance
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tank
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area,
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which
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is
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determined
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from
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plant
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flow
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rate
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and
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required
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up-flow
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velocity
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through
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the
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entrance
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tank.
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The
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width
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of
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the
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entrance
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tank
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is
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chosen
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so
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that
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it
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meets
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the
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geometry
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requirements,
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as
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well
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as
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the
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width
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required
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for
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rapid
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mix.
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In
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the
...
...
...
,
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the
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width
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of
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the
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entrance
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channel
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needs
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to
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be
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at
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least
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the
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the
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spacing
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between
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the
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floc
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baffles
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in
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the
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first
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channel
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(S.FlocBaffle0).
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| Latex |
|---|
...
\large
$$
W_{Et} = \max \left( {{{A_{Et} } \over {L_{Et} }},W_{EtChannel} } \right)
$$
|
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Rapid Mixer
The rapid mix system is designed to mix the alum and raw water on both the macro and micro-mixing scale.
The rapid mix system is centered in the middle of the entrance tank (RM.origin)
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and
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consists
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of
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a
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pipes
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with
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interfaces
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that
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produce
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head
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losses
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through
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changes
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in
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diameter.
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The
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desired
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total
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head
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loss
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throughout
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the
...
entire
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plant
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(HL.PlantTotal)
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is
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40
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cm
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and
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the
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head
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loss
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for
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the
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rapid
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mix
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system
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(h.totalRM)
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is
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determined
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by
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subtracting
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the
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head
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losses
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throughout
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the
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plant
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from
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this
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value.
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The
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head
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loss
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for
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the
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macro-mixing
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orifice
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is
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constrained
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at
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5
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cm
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(MacroMHConstraint),
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so
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the
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micromixing
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orifice
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size
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and
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number
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accounts
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for
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the
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head
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loss
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discrepancies
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that
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need
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to
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be
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met.
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The
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head
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loss
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at
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the
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macro-mixing
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orifice
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should
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suffice
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to
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mix
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the
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water
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and
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alum
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on
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a
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macro
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scale,
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while
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the
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micro-mixing
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orifices
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mix
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on
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a
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molecular
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(micro)
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level.
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The
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elevation
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of
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the
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rapid
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mix
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system
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is
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determined
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from
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the
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height
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of
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the
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weir
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at
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the
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end
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of
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the
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sedimentation
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tank,
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so
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when
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there
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is
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no
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head
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there
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is
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no
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flow
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through
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the
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plant.
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Only
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a
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water
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level
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above
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the
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rapid
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mix
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system
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can
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drive
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the
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plant.
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The
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bottom
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of
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the
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rapid
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mix
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system
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is
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at
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a
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height
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the
...
thickness
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of
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the
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plant
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concrete,
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and
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the
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size
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of
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an
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elbow
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above
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the
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bottom
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of
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the
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plant
...
origin.
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The
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length
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of
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the
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pipe
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is
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determined
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in
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the
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Rapid
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Mixer
...
design
...
program.
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The
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nominal
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diameter
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of
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the
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pipes
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and
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elbows
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that
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are
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part
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of
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the
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rapid
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mix
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system
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is
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determined
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from
...
the
...
required
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head
...
loss
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desired
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throughout
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the
...
plant
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and
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the
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length
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of
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pipe
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and
...
elbow
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needed
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to
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provide
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the
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rapid
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mix
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system
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and
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connect
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to
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the
...
flocculator.
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Since
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the
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entrance
...
tank
...
is
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situated
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next
...
to
...
the
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chemical
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storage
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tanks,
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the
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system
...
must
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be
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connected
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to
...
the
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flocculator
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with
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additional
...
pipes
...
than
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just
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the
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pipe
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that
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runs
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vertically
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through
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the
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entrance
...
tank.
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The
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pipe
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must
...
span
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the
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walkway
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between
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the
...
flocculator
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and
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the
...
entrance
...
tank
...
and
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if
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there
...
is
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an
...
even number
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of
...
flocculation
...
tanks,
...
the
...
pipe
...
must
...
run
...
the
...
entire
...
length
...
of
...
the
...
tank
...
(L.Sed).
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This
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total
...
length
...
-
...
that
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is,
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the
...
length
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of
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the
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pipe
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in
...
the
...
tank,
...
and
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the
...
length
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of
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the
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pipe
...
joins
...
this
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pipe
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(via
...
elbows)
...
to
...
the
...
flocculation
...
tank
...
is
...
the
...
length
...
that
...
is
...
used
...
in
...
the
...
head
...
loss
...
considerations
...
that
...
calculate
...
the
...
nominal
...
diameter
...
of
...
the
...
pipe
...
system
...
as
...
well
...
as
...
the
...
diameter
...
of
...
the
...
macromixing
...
orifice
...
and
...
the
...
size
...
and
...
diameter
...
of
...
the
...
micromixing
...
orifice.
...
The
...
macromixing
...
orifice
...
is
...
a
...
cap
...
that
...
sits
...
atop
...
the
...
pipe
...
in
...
the
...
entrance
...
tank
...
and
...
has
...
a
...
hole
...
in
...
it
...
of
...
the
...
size
...
of
...
the
...
macromix
...
orifice
...
diameter.
...
A length of two pipe diameters is necessary to ensure adequate mixing. A coupling will allow the pipe to run through the bottom of the tank. To ensure enough room for mixing, the micromixing interface will be located at the junction of the pipe and the first elbow.
Macro-Mix Orifice:
