|
|
|
|
DAMPER:
Change
in
pressure,
or
pressure
drop,
that
occurs
across
a
piece
of
control
equipment.
dbA:
Sound-pressure
level
corrected
to
the
“A”
weighing
network.
DECIBEL:
The
logarithmic
ratio
between
some
known
reference
and
some
quantity
of
electrical
or
acoustic
signal
power.
DELTA
P
(?P):
Change
in
pressure,
or
pressure
drop,
that
occurs
across
a
piece
of
control
equipment.
DENIER:
The
weight
in
grams
that
9,000
meters
of
a
fiber
weighs.
DENSITY:
The
measure
of
unit
mass
equal
to
its
weight,
divided
by
its
volume
(lbs/ft3);
standard
air
is
0.075
lbs/ft3.
DENSITY
FACTOR:
Ratio
of
actual
air
density
to
density
of
standard
air.
The
product
of
the
density
factor
and
the
density
of
standard
air
(0.075
lbs/ft3)
will
give
the
actual
air
density
in
pounds
per
cubic
foot.
DEW
POINT:
The
temperature
at
which
the
equilibrium
vapor
pressure
of
a
liquid
is
equal
to
the
existing
partial
pressure
of
the
respective
vapor.
(For
air
containing
water
vapor,
it
is
the
temperature
at
which
liquid
water
begins
to
condense
for
a
given
state
of
humidity
and
pressure
as
the
temperature
is
reduced.
For
flue
gas
containing
water
vapor
and
SO3,
it
is
the
set
of
conditions
at
which
liquid
sulfuric
acid
begins
to
condense
as
the
temperature
is
reduced.)
DFT:
Dry-film
thickness
usually
expressed
in
thousandths
of
an
inch
(mils).
DIAPHRAGM
VALVE:
Compressed
air
valve
on
reverse
pulse
dust
collectors.
Valve
consists
of
an
elastomer
diaphragm
in
a
cast
aluminum
housing.
When
pressure
is
released
from
the
back
of
the
diaphragm,
the
valve
opens
and
allows
the
compressed
air
to
flow
from
the
air
manifold
into
the
oulse
pipe
for
filter
cleaning.
DIFFUSION:
Takes
place
on
particles
so
small
that
their
direction
and
velocity
are
influenced
by
molecular
collisions.
These
particles
do
not
follow
the
air
stream,
but
behave
more
like
gases
than
particulate.
They
move
across
the
direction
of
air
flow
in
a
random
fashion.
When
a
particle
does
strike
a
fiber,
it
is
retained
by
the
van
der
Waals
forces
existing
between
the
particle
and
the
fiber.
DILUTION
VENTILATING:
The
mixing
of
contaminated
air
with
uncontaminated
supply
air
for
the
purpose
of
obtaining
acceptable
working
or
living
conditions.
DOP:
Acronym
for
dioctylphthalate,
a
chemical
used
in
aerosol
form
to
nondestructively
test
high
efficiency
particulate
air
(HEPA)
filters.
DOUBLE
BAG:
Features
a
conventional
bag
on
a
cage
and
an
inner
bag
that
filters
from
inside
out,
with
the
bottom
open
for
dirty
air
entrance.
Puts
more,
but
not
necessarily
effective,
cloth
area
in
a
given
size
baghouse.
DRY
BULB
TEMPERATURE:
The
actual
temperature
of
a
gas,
taken
with
a
conventional
thermometer.
DRY
COLLECTOR:
Dust
collectors
that
use
mechanical
means
(centrifugal
force,
impingement,
filtration)
to
remove
particulate
matter
from
exhaust
gas,
such
as
expansion
chambers,
knockout
boxes,
centrifugal
collectors,
cartridge
filters
and
baghouses.
Devices
not
using
H2O.
DSCFM
(DRY
STANDARD
CUBIC
FEET
PER
MINUTE):
See
gas
flow
rate.
DUCT
SILENCER:
Insulated
section
of
ductwork
connected
to
the
outlet
of
a
fan
to
attenuate
sound.
Silencers
are
available
in
various
sizes
and
are
designed
to
achieve
the
desired
level
of
noise
reduction.
DUST:
Fine,
dry
particles
of
matter
which
may
be
generated
by
mechanical
action
(sawing,
grinding,
drilling,
etc.).
Dust
may
also
be
generated
by
operations
such
as
mixing,
blending,
conveying,
etc.
of
fine
powders.
DUST
CAKE:
The
dust
particle
build-up
on
a
filter
substrate
that
gives
the
air
cleaner
the
ability
to
collect
contaminants
with
high
efficiency.
DUST
COLLECTOR:
An
air-cleaning
device
used
to
remove
heavy
particulate
loadings
from
exhaust
systems
prior
to
discharge.
DUST
COLLECTOR,
CYCLONE:
A
mechanical
device
that
utilizes
the
centrifugal
force
of
the
inlet
gas
to
remove
large
particulate
matter
suspended
in
the
gas.
DUST
COLLECTOR
EFFICIENCY:
See
Collecting
Efficiency.
DUST
PERMEABILITY:
The
mass
of
dust
(grains)
per
square
foot
of
media
divided
by
the
resistance
(pressure
drop)
in
inches
of
water
gauge
(WG)
per
unit
of
filtering
velocity,
feet
per
minute
(fpm).
Not
to
be
compared
with
cloth
permeability.
DWDI:
Double-width,
double-inlet
fans.
DYNAMIC
BALANCE:
The
mechanical
balancing
of
a
rotating
part
or
assembly
in
motion.
DYNAMIC
INSERTION
LOSS:
A
reduction
of
airborne
noise
levels
affected
by
the
installation
of
an
acoustical
silencer.
-
Back
to
top
|
|
|
|