Recirculation of flocs in settling column
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h1. Recirculation of flocs in settling column {composition-setup} cloak.toggle.exclusive=false {composition-setup} h2. |
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{toggle-cloak:id=Concerns} |
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Concerns {cloak:id=Concerns} |
The
...
Tube
...
Floc
...
team
...
observed
...
a
...
slow
...
but
...
seemingly
...
interminable
...
recirculation
...
of
...
flocs
...
inside
...
the
...
settling
...
column
...
during
...
the
...
settling
...
state
...
of
...
each
...
experimental
...
run.
...
This
...
recirculation
...
was
...
troubling
...
because
...
it
...
violated
...
our
...
assumption
...
that
...
the
...
fluid
...
inside
...
the
...
settling
...
column
...
was
...
quiescent
...
enough
...
to
...
allow
...
flocs
...
to
...
be
...
accelerated
...
only
...
by
...
gravity.
...
Since
...
the
...
experimental
...
apparatus
...
was
...
designed
...
to
...
observe
...
floc
...
sedimentation
...
inside
...
the
...
settling
...
column,
...
if
...
flocs
...
were
...
actually
...
being
...
accelerated
...
by
...
a
...
recirculating
...
flow,
...
the
...
data
...
we
...
had
...
collected
...
cannot
...
be
...
interpreted
...
as
...
information
...
about
...
floc
...
sedimentation.
...
This
...
recirculation
...
problem
...
may
...
be
...
a
...
reason
...
for
...
why
...
we
...
have
...
not
...
been
...
seeing
...
ideal
...
settling
...
curves
...
as
...
we
...
would
...
have
...
expected
...
in
...
our
...
results.
...
Changes
...
need
...
to
...
be
...
made
...
to
...
assure
...
that
...
the
...
settling
...
column
...
is
...
quiescent
...
during
...
the
...
settle
...
state,
...
or
...
a
...
new
...
approach
...
must
...
be
...
taken
...
to
...
interpret
...
the
...
data.
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{cloak} h2. |
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{toggle-cloak:id=Possible Causes} |
...
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Causes {cloak:id=Possible Causes} |
Upon
...
identifying
...
the
...
recirculation
...
problem
...
and
...
bringing
...
it
...
up
...
with
...
Dr.
...
Weber-Shirk,
...
the
...
Tube
...
Floc
...
team
...
attempted
...
to
...
identify
...
the
...
cause
...
of
...
the
...
recirculation
...
problem.
...
After
...
weeks
...
of
...
diagnosing
...
the
...
experimental
...
apparatus,
...
the
...
team
...
was
...
able
...
to
...
identify
...
several
...
potential
...
causes
...
for
...
the
...
recirculation:
...
- The
...
- 90
...
- degree
...
- elbow
...
- connectors
...
- at
...
- each
...
- end
...
- of
...
- the
...
- settling
...
- column
...
- was
...
- originally
...
- thought
...
- to
...
- be
...
- the
...
- cause
...
- of
...
- the
...
- circulation
...
- because
...
- such
...
- a
...
- sharp
...
- turn
...
- was
...
- bound
...
- to
...
- introduce
...
- some
...
- vorticity
...
- into
...
- the
...
- flow.
...
- Although
...
- the
...
- recirculation
...
- occurred
...
- after
...
- the
...
- mean
...
- flow
...
- has
...
- been
...
- stopped,
...
- the
...
- redirection
...
- of
...
- momentum
...
- caused
...
- by
...
- the
...
- 90
...
- degree
...
- bend
...
- may
...
- still
...
- have
...
- lingered
...
- and
...
- thus
...
- could
...
- have
...
- contributed
...
- to
...
- the
...
- recirculation.
...
- The
...
- connection
...
- between
...
- the
...
- 3/8
...
- inch
...
- diameter
...
- flocculator
...
- tube
...
- and
...
- the
...
- 1/2
...
- inch
...
- settling
...
- column
...
- has
...
- always
...
- been
...
- a
...
- source
...
- of
...
- concern.
...
- The
...
- abrupt
...
- change
...
- from
...
- small
...
- to
...
- big
...
- diameter
...
- should
...
- theoretically
...
- cause
...
- flow
...
- instabilities
...
- that
...
- could
...
- lead
...
- to
...
- the
...
- formation
...
- of
...
- turbulent
...
- eddies.
...
- Moreover,
...
- the
...
- jaggedness
...
- of
...
- the
...
- inner
...
- walls
...
- of
...
- the
...
- pipe
...
- connectors
...
- will
...
- also
...
- interrupt
...
- the
...
- stability
...
- of
...
- the
...
- flow
...
- and
...
- compound
...
- the
...
- problem.
...
- A
...
- solution
...
- to
...
- this
...
- problem
...
- would
...
- be
...
- to
...
- fabricate
...
- a
...
- cone
...
- shaped
...
- connector
...
- that
...
- could
...
- provide
...
- a
...
- smooth
...
- and
...
- very
...
- gradual
...
- transition
...
- from
...
- small
...
- to
...
- large
...
- diameter.
...
- This
...
- connector
...
- would
...
- need
...
- to
...
- have
...
- a
...
- small
...
- enough
...
- angle
...
- to
...
- the
...
- axis
...
- of
...
- the
...
- column
...
- to
...
- ensure
...
- that
...
- the
...
- adverse
...
- pressure
...
- gradient
...
- created
...
- by
...
- the
...
- increase
...
- in
...
- diameter
...
- is
...
- weak
...
- enough
...
- that
...
- it
...
- will
...
- not
...
- cause
...
- flow
...
- separation
...
- at
...
- the
...
- boundary
...
- of
...
- the
...
- pipe.
...
- We
...
- noticed
...
- that
...
- the
...
- recirculation
...
- began
...
- the
...
- moment
...
- the
...
- valves
...
- were
...
- shut
...
- off.
...
- Since
...
- the
...
- solenoid
...
- valves
...
- close
...
- very
...
- abruptly,
...
- a
...
- small
...
- volume
...
- of
...
- fluid
...
- is
...
- displaced
...
- in
...
- an
...
- extremely
...
- short
...
- period
...
- of
...
- time
...
- each
...
- time
...
- a
...
- valve
...
- closes.
...
- This
...
- pulse
...
- of
...
- momentum
...
- may
...
- be
...
- strong
...
- enough
...
- that
...
- it
...
- traveled
...
- through
...
- the
...
- tubes
...
- and
...
- into
...
- the
...
- settling
...
- column
...
- where
...
- it
...
- may
...
- create
...
- instabilities
...
- leading
...
- to
...
- vorticity.
...
- The
...
- tungsten
...
- lamp
...
- that
...
- generates
...
- the
...
- white
...
- light
...
- inside
...
- the
...
- turbidimeter
...
- radiates
...
- a
...
- significant
...
- amount
...
- of
...
- heat
...
- to
...
- the
...
- settling
...
- column.
...
- Some
...
- summer
...
- students
...
- had
...
- performed
...
- a
...
- heat
...
- test
...
- which
...
- concluded
...
- that
...
- the
...
- heat
...
- generated
...
- by
...
- the
...
- lamp
...
- did
...
- not
...
- affect
...
- the
...
- turbidimeter's
...
- ability
...
- to
...
- measure
...
- turbidity
...
- accurately;
...
- however,
...
- because
...
- the
...
- heat
...
- tests
...
- had
...
- been
...
- performed
...
- using
...
- mixtures
...
- containing
...
- very
...
- fine
...
- clay
...
- particles,
...
- the
...
- effects
...
- of
...
- density
...
- driven
...
- convection
...
- was
...
- not
...
- apparent
...
- in
...
- the
...
- turbidity
...
- readings.
...
- If
...
- the
...
- heat
...
- transfer
...
- between
...
- the
...
- lamp
...
- and
...
- water
...
- was
...
- large
...
- enough,
...
- the
...
- change
...
- in
...
- the
...
- local
...
- density
...
- of
...
- fluid
...
- would
...
- cause
...
- convection
...
- currents
...
- that
...
- could
...
- potentially
...
- create
...
- the
...
- type
...
- of
...
- circulation
...
- we
...
- have
...
- been
...
- observing.
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{cloak} h2. |
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{toggle-cloak:id=Visual Experimentation} |
...
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Experimentation {cloak:id=Visual Experimentation} |
Several
...
visual
...
experiments
...
were
...
conducted
...
to
...
determine
...
what
...
the
...
actual
...
cause
...
of
...
the
...
reciruclation
...
was
...
from.
...
First,
...
we
...
conducted
...
experiments
...
changing
...
the
...
pump
...
control
...
shutoff,
...
then
...
we
...
experimented
...
with
...
the
...
changing
...
diameter
...
of
...
the
...
elbow
...
to
...
the
...
column,
...
and
...
lastly,
...
we
...
experimented
...
with
...
the
...
heat
...
factor.
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{cloak} h3. |
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{toggle-cloak:id=Pump Control Shutoff} |
...
...
Control Shutoff
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Shutoff {cloak:id=Pump Control Shutoff} |
We
...
ran
...
some
...
tests
...
to
...
gauge
...
what
...
contribution
...
the
...
sudden
...
stoppage
...
of
...
flow
...
had
...
on
...
the
...
recirculation
...
problem.
...
First,
...
we
...
introduced
...
a
...
new
...
Process
...
Controller
...
state
...
between
...
the
...
Loading
...
state
...
and
...
the
...
Settle
...
state
...
that
...
allowed
...
the
...
pumps
...
to
...
ramp
...
down
...
before
...
shutting
...
off.
...
We
...
hypothesized
...
that
...
a
...
more
...
gradual
...
reduction
...
in
...
flow
...
rate
...
would
...
provide
...
an
...
improvement
...
over
...
abrupt
...
shut-off.
...
We
...
also
...
wanted
...
to
...
see
...
the
...
effects
...
of
...
shutting
...
the
...
valves
...
verses
...
not
...
shutting
...
the
...
valves,
...
so
...
we
...
ran
...
some
...
test
...
without
...
shutting
...
the
...
valves.
...
After
...
careful
...
observation,
...
we
...
concluded
...
that
...
the
...
recirculation
...
was
...
occurring
...
even
...
without
...
the
...
valve
...
shut-off
...
(about
...
20-30
...
seconds
...
into
...
settling
...
state.)
...
We
...
did
...
observe
...
a
...
slight
...
reduction
...
in
...
the
...
intensity
...
of
...
the
...
circulation
...
with
...
the
...
increase
...
in
...
ramp
...
down
...
time,
...
but
...
circulation
...
was
...
still
...
observed
...
after
...
a
...
ramp
...
down
...
time
...
of
...
60
...
seconds.
...
The
...
instabilities
...
maybe
...
a
...
result
...
of
...
either
...
the
...
pump
...
shutoff
...
causing
...
a
...
"push/pull"
...
in
...
the
...
water
...
(even
...
though
...
the
...
pump
...
is
...
being
...
ramped
...
down,
...
there
...
is
...
still
...
a
...
slight
...
pressure
...
change
...
when
...
the
...
pump
...
is
...
completely
...
shutoff)
...
or
...
from
...
the
...
diameter
...
change
...
from
...
the
...
flocculator
...
tube
...
to
...
the
...
settling
...
column
...
causing
...
eddies
...
of
...
turbulence
...
in
...
the
...
top
...
of
...
the
...
column.
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{cloak} h3. |
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{toggle-cloak:id=Elbow Connections} |
...
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Connections {cloak:id=Elbow Connections} |
Another
...
possible
...
source
...
of
...
recirculation
...
in
...
the
...
settling
...
column
...
is
...
the
...
elbow
...
connections.
...
The
...
settling
...
column
...
is
...
bounded
...
by
...
both
...
an
...
elbow
...
connection
...
coming
...
into
...
the
...
column
...
and
...
going
...
out
...
of
...
the
...
column.
...
Not
...
only
...
do
...
these
...
connections
...
cause
...
a
...
sharp
...
turn
...
in
...
flow,
...
but
...
there
...
is
...
a
...
diameter
...
change
...
between
...
the
...
elbow
...
and
...
the
...
column.
...
The
...
change
...
in
...
diameter
...
could
...
be
...
causing
...
preferential
...
flow
...
in
...
the
...
column,
...
therefore,
...
a
...
recirculation
...
current.
...
The
...
recirculation
...
occurs
...
over
...
the
...
entire
...
diameter
...
length
...
scale
...
of
...
the
...
column;
...
therefore,
...
if
...
these
...
large
...
eddies
...
could
...
be
...
made
...
smaller,
...
either
...
viscosity
...
will
...
dampen
...
the
...
smaller
...
eddies
...
out
...
or
...
the
...
recirculation
...
would
...
be
...
confined
...
to
...
small
...
scales.
...
We
...
tried
...
to
...
implement
...
a
...
technique
...
similar
...
to
...
the
...
use
...
of
...
honeycomb
...
screens
...
in
...
wind-tunnels
...
to
...
homogenize
...
flow
...
by
...
placing
...
a
...
bundle
...
of
...
plastic
...
drinking
...
straws
...
that
...
had
...
been
...
cut
...
to
...
2.5
...
inches
...
in
...
the
...
upper
...
portion
...
of
...
the
...
settling
...
column
...
where
...
the
...
column
...
attaches
...
to
...
the
...
elbow
...
connection.
...
This,
...
the
...
team
...
thought,
...
would
...
help
...
to
...
reduce
...
the
...
preferential
...
flow
...
pattern
...
that
...
could
...
be
...
caused
...
by
...
the
...
change
...
in
...
diameter.
...
After
...
placing
...
the
...
straws
...
into
...
the
...
settling
...
column,
...
we
...
observed
...
that
...
the
...
recirculation
...
currents
...
were
...
reduced.
...
It
...
is
...
important
...
to
...
note
...
for
...
the
...
next
...
experiment
...
that
...
the
...
majority
...
of
...
these
...
elbow
...
experiments
...
were
...
conducted
...
with
...
the
...
settling
...
column
...
outside
...
the
...
turbidimeter.
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{cloak} |
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{toggle-cloak:id=Heat Induced Currents} |
...
...
Induced Currents
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Currents {cloak:id=Heat Induced Currents} |
Next,
...
it
...
was
...
hypothesized
...
that
...
the
...
heat
...
produced
...
from
...
the
...
tungsten
...
lightbulb
...
in
...
the
...
turbidimeter
...
may
...
be
...
causing
...
the
...
recirculation.
...
Comparison
...
experiments
...
were
...
conducted
...
with
...
the
...
settling
...
column
...
outside
...
the
...
turbidimeter,
...
where
...
heat
...
from
...
the
...
lamp
...
would
...
not
...
be
...
an
...
issue,
...
and
...
inside
...
the
...
turbidimeter,
...
where
...
the
...
heat
...
could
...
have
...
an
...
affect
...
on
...
the
...
column.
...
When
...
the
...
column
...
was
...
placed
...
outside
...
the
...
turbidimeter,
...
little
...
to
...
no
...
recirculation
...
was
...
observed.
...
However,
...
recirculation
...
currents
...
were
...
clearly
...
visible
...
when
...
the
...
column
...
was
...
inside
...
the
...
turbidimeter,
...
Figure. Flocs in the tube showing the ideal condition when there is no heat is applied (left) and when heat is applied to the settling tube (right).
In order to ensure that heat may be the determining factor, the team wanted to test whether another type of heat source would cause recirculation. The settling column was placed outside the turbidimeter but when the experiment came to the settling state, a team member wrapped their hand around one part of the column to provide a heat source. Once again, recirculation was visible and the team determined that heat was definitely the major contributing source to recirculation in the settling column.
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{cloak} |
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{toggle-cloak:id=Conclusions} |
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Conclusions {cloak:id=Conclusions} |
While
...
the
...
recirculation
...
problem
...
in
...
the
...
settling
...
column
...
was
...
finally
...
treated
...
by
...
removing
...
the
...
heat
...
source
...
from
...
the
...
column,
...
the
...
team
...
believes
...
that
...
the
...
problem
...
could
...
have
...
been
...
caused
...
by
...
several
...
different
...
sources
...
and
...
the
...
culmination
...
of
...
all
...
of
...
these
...
experiments
...
probably
...
helped
...
in
...
solving
...
the
...
recirculation
...
currents.
...
To
...
remove
...
the
...
heat
...
source,
...
the
...
team
...
is
...
working
...
with
...
HF
...
Scientific
...
to
...
replace
...
the
...
IR
...
lamp
...
with
...
a
...
non-heat
...
producing
...
...
...
.
...
Additionally,
...
the
...
team
...
has
...
replaced
...
the
...
elbow
...
connections
...
with
...
straight
...
connections.
...
In
...
order
...
to
...
be
...
able
...
to
...
use
...
these
...
straight
...
connections,
...
the
...
team
...
needs
...
to
...
figure
...
out
...
a
...
way
...
to
...
stop
...
the
...
flow
...
traveling
...
into
...
the
...
settling
...
column
...
after
...
the
...
settle
...
state
...
has
...
begun,
...
in
...
order
...
to
...
prevent
...
watching
...
the
...
settling
...
of
...
a
...
long
...
vertical
...
tube
...
besides
...
just
...
the
...
sample
...
in
...
the
...
settling
...
column.
...
By
...
introducing
...
a
...
slanted
...
tube
...
with
...
a
...
simple
...
trap
...
before
...
the
...
tube
...
inlet,
...
the
...
team
...
has
...
managed
...
to
...
collect
...
settling
...
flocs
...
in
...
the
...
tube
...
from
...
the
...
top
...
of
...
the
...
board
...
during
...
no-flow
...
state.
...
Also,
...
the
...
team
...
will
...
determine
...
whether
...
or
...
not
...
the
...
straws
...
are
...
helping
...
to
...
reduce
...
the
...
recirculation
...
problem
...
even
...
after
...
the
...
straight
...
connections
...
have
...
been
...
added
...
and
...
the
...
heat
...
source
...
is
...
removed,
...
or
...
if
...
they
...
are
...
unnecessary.
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