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IMPELLER:
Another
term
for
fan
“wheel”.
The
rotating
portion
of
the
fan
designed
to
increase
the
energy
level
of
the
gas
stream.
IMPELLER
DIAMETER:
The
maximum
diameter
measured
over
the
impeller
blade.
IMPINGEMENT:
When
air
flows
through
a
filter,
it
changes
direction
as
it
passes
around
each
fiber.
Larger
dust
particles,
however,
cannot
follow
the
abrupt
changes
in
direction
because
of
their
inertia.
As
a
result,
they
do
not
follow
the
air
stream
and
collide
with
a
fiber.
INCH
OF
WATER:
A
unit
of
pressure
equal
to
the
pressure
exerted
by
a
column
of
water,
one
inch
high
at
a
standard
temperature.
(407”
WG
=
14.7
PSI)
INCHES
WG
(INCHES
OF
WATER
GAUGE):
See
Inch
of
Water.
INCINERATOR:
A
device
that
burns
household,
industrial,
pathological
or
hazardous
solid,
liquid
or
gaseous
wastes
under
controlled
conditions.
INCLINED
MANOMETER:
A
testing
instrument
using
a
liquid
column,
set
at
an
incline
to
increase
reading
accuracy,
to
measure
pressure.
Normally
used
to
read
velocity
pressure.
INDUCED
DRAFT:
How
air
is
provided
in
a
process,
such
as
a
combustion
process;
where
air
is
drawn
or
pulled
through
a
process.
Also
see
Forced
Draft.
INDUCTION:
The
production
of
an
electric
current
in
a
conductor
in
a
changing
magnetic
field.
INERTIA:
Tendency
of
an
object
to
remain
in
the
state
it
is
in.
See
WR2.
INERTIAL
SEPARATORS:
Air
pollution
control
equipment
that
uses
the
principle
of
inertia
to
remove
particulate
matter
from
a
stream
of
air
or
gas.
See
mechanical
and
cyclone
collectors.
INLET
DIFFUSER
PLENUM:
Air
transition
chamber
between
high-velocity
ductwork
and
an
air
cleaner.
The
purpose
of
the
inlet
plenum
is
to
slow
the
incoming
airstream
down
to
the
collector
velocity
and
provide
even
air
distribution
across
the
face
of
the
air
cleaner.
INLET-VANE
DAMPER:
Round
multiblade
damper
mounted
to
the
inlet
of
a
fan
to
vary
the
airflow.
INSTABILITY:
The
point
of
operation
at
which
a
fan
or
system
will
“hunt”
or
pulse.
Common
in
FC
fans
and
some
other
fan
types
where
the
point
of
operation
is
left
of
the
peak
of
the
static-pressure
curve.
INSULATION:
Any
method
which
will
retard
the
flow
of
heat
through
a
wall.
In
baghouses,
it
is
commonly
a
lightweight
fiberglass
mat.
INTERCEPTION:
A
special
case
of
impingement
where
a
particle
is
small
enough
to
move
with
the
air
stream
but,
because
its
size
is
very
small
in
relation
to
the
fiber,
makes
contact
with
a
fiber
while
following
the
tortuous
airflow
path
of
the
filter.
The
contact
is
not
dependent
on
inertia
and
the
particle
is
retained
on
the
fiber
because
of
the
inherent
adhesive
forces
that
exist
between
the
particle
and
fiber.
These
forces,
called
van
der
Waals
forces,
enable
a
fiber
to
trap
a
particle
without
the
use
of
inertia.
INTERSTICES:
The
openings
between
the
interlacings
of
the
warp
and
filling
yarns,
such
as
the
voids.
INVERSION:
An
atmospheric
condition
caused
by
a
layer
of
warm
air
preventing
the
rise
of
cooling
air
trapped
beneath
it.
This
prevents
the
rise
of
pollutants
that
might
otherwise
be
dispersed
and
results
in
a
concentration
of
the
air
pollution.
INTERSTITIAL
VELOCITY:
The
apparent
velocity
of
a
gas
as
it
passes
by
a
filter
bag
matrix.
It
is
found
by
dividing
the
collector
gas
volume
by
the
cross
sectional
area,
after
the
cross
sectional
of
the
bags
have
been
subtracted
from
the
collector
cross
sectional
area.
IONIZER:
Set
of
fine
wires
suspended
between
grounded
plates
in
SMOG-HOG
electrostatic
precipitators
where
particle
charging
occurs.
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