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6.
DESCRIPTION
6.1.
OPERATINGPRINCIPLE
All the dryers described
in
this manual operate
on
the same principle.
A refrigeralion circuit reduces the temperature
of
a patenled
'thermal
mass" lhrough which the humid compressed
air
to
be
dried
is
passed.
As
the
air is
cooled
its
water vapour condenses and
is
lhen separated and drained.
The
temperature
of
the thermal mass
is
controlled
by
an elecironic
board
which
stops
the compressor when
it
reaches lhe ,ixed set
point.
6.2.
AIR AND REFRIGERATION CIRCUITS
(See
attached refrigerant drawlngs)
Compressed air
circuit
The warm, wet compressed air
enters
the dryer and
passes
lhrough lhe
airtoair
heat
exchanger seclion
of the
thermal mass
Here
it
is
pr+cooled
by
the cold,
dry
compressed air
leaving
the
air-tcrefrigeranl
heat
exchanger seclion
or
the evaporator
of
the thermal
mass.
The
pre-cooled
air then
enters
the
evaporator seclion
of the thermal
mass where
it
is
cooled
(in
most applicalions
to
a
temperatur€
of
approximalely
3'C
/
37.4'F)
exchanging
heat
with lhe evaporator refrigerant fluid
and
the silica thermal
mass.
The heat is exchanged by conduclion through
the
aluminium fins connecting the copper tubes, inside which the compressed
aar
flo\,s, lo
the copper tubes, inside which
the refrigerant fluid evaporales.
The aluminium fins also exchange
heat
with the
silica
thermal mass keeping
it at a
temperalure
of
approximately 0"C
(32'F).
At
this
stage,
the compressed air
is in a
saturaled state and entrains lhe condensed moislure produced during cooling.
It
then
passes into
the
high efiiciency condensate separator (demister type
with
slainless
sleel
mesh) where
the
entrained moisture
is
precipilaled
out of lhe air
and
collects
at
the bottom
of
the separator.
A
timed or intelligenl (depending
on
the
unit
contiguration (S3) condensate discharger opens
at
intervals
to
force the condensate from the dryer wilh compressed
air.
The cold,
dry
air leaving the separator then flows for
a
second time through the
air-loair
heat
exchanger seclion
of
the thermal
mass
where
it
is reheated while pre,cooling
the warm wet
air
entering the
dryer.
Not only does
this air-toair
heat exchanger reduce
the
energy consumption required
lo
dry
a
given quantity
of
compressed
air,
but
il
also prevents condensation from
forming
on
the dryer outlel.
Refrigeration
circuit
The r€frigerant gas is pumped
at
high pressure
by a
hermetically sealed compressor
to
the condenser.
Here
the cooling aclion causes the refrigerant
gas to
condense to
a
liquid.
The refrigeranl condenser
may be air or
water cooled (S3).
Air-cooled condenser
The condenser
is a
linned coil heal exchanger cooled
by a
flo{,r,
of
air provided
by an
eledrically driven fan
The condenser
is
generously sized
in
order to be partially used
as a
liquid
receiver.
Water-cooled condenser
This condenser
is a
lubein-lube
heat
exchanger (copper lubes inside
a
carbon sleel ouler tube)
in
which lhe water flows inside the exchanger tubes.
The
cooling
water enters the
rear of the
dryer
and
flows lhrough a pressure regulating valve before entering the condenser.
The pressure regulating valve conlrols the cooling water flow
lo
ensure
that condensing pressure does
not
fall below
a
pre-set
value.
Afler the condenser, lhe liquid refrigerant then
passes
through
a
filterdryer
to
a
capillary tube which reduces its pressure
in
order
lo
lower its boiling point.
The refrigerant then enters the
evaporator
tubes
in the
lhermal mass
and
cools
both the
thermal
mass
and the compressed
air.
The refrigerant leaving the evaporator
is now a
cold vapour and relums lo lhe compressor to repeal the cycle
Since
the
heat
of the
compressed
air
available
lo
evaporate
the
refrigerant varies considerably due
to
flucluations in
the
air
flow
rate
and
inlet temperature,
lhe
dryer
features
an
eleclronic system which
controls
the lemperalure
of
the thermal
mass
lemperature, thereby achieving
3
important objeclives:
lo
ensure
lhat th€ dew-point under pressure is maintained
at a
constant value
of
approximately +3"C (+37.4"F);
to prevent the compressed
air
temperature from falling
belov
0"C (32"F),
a
temperature
at
which the condensed moislure could starl
to
freeze;
to ensure lhat
all
the refrigerant
leaving
the evaporalor
is in the
form
of a
vapour
so
that
no
liquid retrigeranl relurns
to
the compressor
Vvhen
there is little or
no
load,
the
temperature
in
the thermal mass tends lo
fall.
At
0'C
(32'F), the eleclronic board switches
off
the refrigerant compressor
The compressed
air
that continues
to
flow
in
the evaporator
is
cooled
by
lhe cold energy stored
in
the silica.
Vvhen
the temperature
of
the latter eventually
starts
to increase, the refrigerant compressor
is
aulomatically switched back
on
to cool il down again
This syslem
has
the advantage of
reducing
the average energy consumption
of
the dryer roughly in proportion
to
the demand
6.3.
ELECTRICAL CIRCUIT
Please
see
the attached eleclrical diagrams.
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