...
Exit
...
Channel
...
Design
...
Program
...
The
...
purpose
...
of
...
this
...
program
...
is
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to
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design
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the
...
exit
...
channel
...
and
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the
...
exit
...
weir
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that
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will
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keep
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a
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constant
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water
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level
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throughout
...
the
...
plant
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and
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carry
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treated
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water
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into
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the
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distribution
...
tank.
...
Exit
...
Channel
...
Design
...
Program
...
Algorithm
...
...
...
...
Algorithm
The exit channel program outlines the dimensions of the exit channel, which carries water from the sedimentation tank to the distribution tank. Chlorine is added to the water at the end of the exit channel as it enters the distribution tank. The program also determines the outlet weir dimensions. The outlet weir controls flow to the storage tank and determines the water level throughout the entire plant. The last piece of the plant calculated by this program is the size and length of the sedimentation launders.
Exit Channel Dimensions
The length of the exit channel is found first. The channel is defined to span perpendicular to the sedimentation tanks, and thus its length must always be the total width occupied by all sedimentation tanks.
| Latex |
|---|
Program|AutoCAD Channel Program] h3. Algorithm The exit channel program outlines the dimensions of the exit channel, which carries water from the sedimentation tank to the distribution tank. Chlorine is added to the water at the end of the exit channel as it enters the distribution tank. The program also determines the outlet weir dimensions. The outlet weir controls flow to the storage tank and determines the water level throughout the entire plant. The last piece of the plant calculated by this program is the size and length of the sedimentation launders. h5. Exit Channel Dimensions The length of the exit channel is found first. The channel is defined to span perpendicular to the sedimentation tanks, and thus its length must always be the total width occupied by all sedimentation tanks. {latex} \large $$ L_{ExitChannel} = (N_{SedTanks} )(W_{Sed} ) + (N_{SedTanks} + 1)(T_{PlantWall} ) $$ {latex} |
The
...
width
...
of
...
the
...
exit
...
channel
...
is
...
designed
...
based
...
weir
...
orientation
...
and
...
the
...
constraint
...
that
...
the
...
head
...
loss
...
in
...
the
...
open
...
channel
...
must
...
be
...
very
...
small
...
compared
...
with
...
the
...
head
...
loss
...
in
...
the
...
launder
...
orifices
...
to
...
ensure
...
that
...
the
...
flow
...
is
...
uniformly
...
distributed
...
between
...
sedimentation
...
tank
...
bays.
...
To
...
ensure
...
this
...
the
...
head
...
loss
...
in
...
the
...
channel
...
was
...
chosen
...
to
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be
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twenty
...
times
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smaller
...
than
...
the
...
head
...
loss
...
in
...
the
...
launder.
...
Using
...
the
...
head
...
loss
...
equation
...
this
...
ratio
...
was
...
converted
...
to
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use
...
as
...
an
...
input
...
the
...
ratio
...
of
...
flow
...
between
...
the
...
sedimentation
...
tank
...
with
...
shortest
...
route
...
to
...
the
...
exit
...
channel
...
and
...
the
...
tank
...
with
...
the
...
longest
...
route
...
to
...
the
...
channel.
| Latex |
|---|
} \large $$ h_L = C_{p_1 } {{Q_1 ^2 } \over {2gA^2 }} $$ $$ C_{p_1 } Q_1 ^2 = C_{p_2 } Q_2 ^2 $$ {latex} |
The
...
variable
...
Î
...
loss was
...
assigned
...
a
...
value
...
of
...
1/20,
...
representing
...
the
...
ratio
...
of
...
head
...
loss
...
between
...
the
...
channel
...
and
...
the
...
orifice.
...
The
...
flow
...
ratio
...
was
...
then
...
solved
...
as
...
a
...
function
...
of
...
the
...
loss
...
ratio.
| Latex |
|---|
} \large $$ h_{L_{shortpath} } = {1 \over {\Pi _{loss} }} $$ $$ h_{L_{longpath} } = {1 \over {\Pi _{loss} }} + 1 $$ $$ \Pi _{QSedTanks} = \sqrt {{{{1 \over {\Pi _{loss} }}} \over {{1 \over {\Pi _{loss} }} + 1}}} $$ $$ \Pi _{loss} = {{1 - \Pi _{QSedTanks} ^2 } \over {\Pi _{QSedTanks} ^2 }} $$ {latex} |
For
...
simplicity
...
the
...
channel
...
is
...
assumed
...
to
...
be
...
square
...
(w=b).
...
The
...
code
...
starts
...
with
...
the
...
width
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equal
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to
...
the
...
inlet
...
channel
...
width,
...
then
...
iterates
...
to
...
find
...
the
...
smallest
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width
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that
...
fulfills
...
the
...
head
...
loss
...
requirement.
...
The
...
larger
...
of
...
either
...
a
...
W
...
ExitChannelMin or
...
the
...
returned
...
value
...
from
...
the
...
iteration
...
is
...
returned.
...
W
...
ExitChannelMin is
...
needed
...
to
...
ensure
...
that
...
the
...
tank
...
is
...
large
...
enough
...
for
...
a
...
person
...
to
...
put
...
their
...
hand
...
in
...
the
...
channel
...
to
...
cap
...
the
...
launders.
...
This
...
value
...
is
...
approximately
...
equal
...
to
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1.5*(ND.launder),
...
where
...
ND.launder
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is
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the
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diameter
...
of
...
the
...
launder
...
pipe.
...
The
...
depth
...
of
...
the
...
water
...
in
...
the
...
exit
...
channel
...
is
...
lower
...
than
...
the
...
depth
...
of
...
water
...
in
...
the
...
sedimentation
...
tank
...
by
...
the
...
head
...
loss
...
in
...
the
...
effluent
...
launder.
...
That
...
value
...
is
...
set
...
to
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approximately
...
5
...
cm.
...
The
...
channel
...
walls
...
are
...
as
...
high
...
as
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the
...
walls
...
in
...
the
...
sed
...
tank
...
and
...
thus
...
the
...
freeboard
...
for
...
the
...
channel
...
is
...
the
...
freeboard
...
in
...
the
...
rest
...
of
...
the
...
plant
...
(10
...
cm)
...
plus
...
the
...
head
...
loss
...
in
...
the
...
launder
...
(5
...
cm).
...
Exit
...
Weir
...
Specifications
...
The
...
exit
...
weir
...
controls
...
the
...
flow
...
of
...
water
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leaving
...
the
...
plant
...
and
...
regulates
...
the
...
water
...
heights
...
throughout
...
the
...
plant.
...
The
...
width
...
of
...
the
...
exit
...
weir
...
is
...
designed
...
based
...
on
...
the
...
following
...
equation:
| Latex |
|---|
} \large $$ W = {3 \over 2}{Q \over {K_{VC} \sqrt {2g} H^{{3 \over 2}} }} $$ {latex} |
Where
...
W
...
is
...
the
...
width
...
of
...
the
...
weir
...
and
...
H
...
is
...
the
...
head
...
loss
...
over
...
the
...
weir.
...
There
...
are
...
two
...
possible
...
orientations
...
for
...
the
...
weir:
...
perpendicular
...
to
...
the
...
length
...
of
...
the
...
channel,
...
or
...
parallel.
Parallel Weir
The parallel weir design has the weir placed parallel to the length of the channel and attached to the inner half of the channel. Water flows in from the launders into the inner box created by the weir, and then overflows into the outer channel and into the distribution tank. The channel with the parallel weir is designed so that the outer channel that flows to the distribution tank satisfies the condition that the head loss in the open channel be far less than the head loss in the launder orifices.
Perpendicular Weir
The weir will be placed in the exit channel such that the head loss in the open channel is very small compared with the head loss in the launder orifices so that the flow between sedimentation tank bays is uniformly distributed. The weir must also be designed so that a constant water level is obtained throughout the entire plant.
Sedimentation Tank Exit Launders
Water that leaves the sedimentation tank exits at the top of the tank through holes drilled in pvc pipes that run the length of the tank. The holes drilled in the sides of the pipe ensure uniform flow of water up through the tank. The water exits into the exit channel. The launder parameters to be determined are the launder length, pipe size and orifice size.
The first step to designing the sedimentation launders is to determine the length of the launders. The launders are defined to run the entire length of the sedimentation tank, minus the widths of both the inlet and exit channels.
| Include Page | ||||
|---|---|---|---|---|
|
The size of the launder pipe is dependent on the length of the pipe, the flow through the pipe, an estimated head loss available, and the given acceptable ratio of the flow in the last orifice to the flow through the first orifice. This ratio is assumed to be 0.8 for this program. As a reference, a ratio of 1 indicates that the flow is exactly the same in the first and last holes. Less than 1 indicates some discrepancy. This function (ND.Manifold) is defined in the fluids functions program and returns the nominal diameter for the sedimentation launder (ND.SedLaunder).
The actual head loss through the manifold is found based on the actual diameter of the launder. The function determining head loss is also referenced from the fluids functions program.
The diameter of the launder orifices is calculated from the orifice equation, based on creating uniform flow and designed to have a head loss that is equal to the total head loss designed for the launder minus the frictional head loss through the launder pipe. This equation is also referenced from the fluids function programs. The holes size is important because we need uniform flow to ensure good sedimentation, and the smaller the holes the better the flow uniformity. But smaller holes lead to more head loss which in turn makes the sedimentation tanks deeper and more expensive. This equation reflects the compromise between these parameters of head loss and uniform flow.
The launder should be placed at a height that is as close to the top of the sedimentation tank as possible, but still always under water. The height of launder is placed below the water level in the sedimentation tank by the total head loss through the launder.
The height of the water in the exit channel can now be determined and is defined to be the height of water in the sedimentation tank less the head loss through the sedimentation tank launder. The depth of the exit channel is depth of the water in the exit channel plus the plant free board of 10cm.
| Include Page | ||||
|---|---|---|---|---|
|
The height of the plant weir is the height of the water in the exit channel less the height of the lip of water over the weir.
| Include Page | ||||
|---|---|---|---|---|
|
| Wiki Markup |
|---|
h5. Parallel Weir
The parallel weir design has the weir placed parallel to the length of the channel and attached to the inner half of the channel. Water flows in from the launders into the inner box created by the weir, and then overflows into the outer channel and into the distribution tank. The channel with the parallel weir is designed so that the outer channel that flows to the distribution tank satisfies the condition that the head loss in the open channel be far less than the head loss in the launder orifices.
!Picture1.png!
h5. Perpendicular Weir
The weir will be placed in the exit channel such that the head loss in the open channel is very small compared with the head loss in the launder orifices so that the flow between sedimentation tank bays is uniformly distributed. The weir must also be designed so that a constant water level is obtained throughout the entire plant.
!Drawing1-Mo2del.jpg|thumbnail,align=left!
h5. Sedimentation Tank Exit Launders
Water that leaves the sedimentation tank exits at the top of the tank through holes drilled in pvc pipes that run the length of the tank. The holes drilled in the sides of the pipe ensure uniform flow of water up through the tank. The water exits into the exit channel. The launder parameters to be determined are the launder length, pipe size and orifice size.
The first step to designing the sedimentation launders is to determine the length of the launders. The launders are defined to run the entire length of the sedimentation tank, minus the widths of both the inlet and exit channels.
{include:L.SedLaunder}
The size of the launder pipe is dependent on the length of the pipe, the flow through the pipe, an estimated head loss available, and the given acceptable ratio of the flow in the last orifice to the flow through the first orifice. This ratio is assumed to be 0.8 for this program. As a reference, a ratio of 1 indicates that the flow is exactly the same in the first and last holes. Less than 1 indicates some discrepancy. This function (ND.Manifold) is defined in the [fluids functions program|Fluids Functions Design Program] and returns the nominal diameter for the sedimentation launder (ND.SedLaunder).
The actual head loss through the manifold is found based on the actual diameter of the launder. The function determining head loss is also referenced from the [fluids functions program|Fluids Functions Design Program].
The diameter of the launder orifices is calculated from the orifice equation, based on creating uniform flow and designed to have a head loss that is equal to the total head loss designed for the launder minus the frictional head loss through the launder pipe. This equation is also referenced from the [fluids function programs|Fluids Functions Design Program]. The holes size is important because we need uniform flow to ensure good sedimentation, and the smaller the holes the better the flow uniformity. But smaller holes lead to more head loss which in turn makes the sedimentation tanks deeper and more expensive. This equation reflects the compromise between these parameters of head loss and uniform flow.
The launder should be placed at a height that is as close to the top of the sedimentation tank as possible, but still always under water. The height of launder is placed below the water level in the sedimentation tank by the total head loss through the launder.
The height of the water in the exit channel can now be determined and is defined to be the height of water in the sedimentation tank less the head loss through the sedimentation tank launder. The depth of the exit channel is depth of the water in the exit channel plus the plant free board of 10cm.
{include:HW.ExitChannel}
The height of the plant weir is the height of the water in the exit channel less the height of the lip of water over the weir.
{include:H.PltWeir}
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