Note: Descriptions are shown in the official language in which they were submitted.
CONDENSATION COOLING SYSTEM
FOR GAS TURBINE ENGINE
TECHNICAL FIELD
[0001] The application relates generally to gas turbine engines and,
more
particularly, to a cooling system of a gas turbine engine.
BACKGROUND OF THE ART
[0002] Due to heat generated in the operation of gas turbine engines,
various
methods and system have been developed for rejecting heat of engine systems
such as
the auxiliary gearbox, the integrated drive generator, etc. Heat may be
rejected to
available cooling air, such as air circulating in the bypass duct.
Accordingly, heat
exchangers may project into the bypass duct, but may hence affect air flow and
cause
vibration of the fan. It is also known to position coils of cooling oil near
or at the surface
of the bypass duct, bringing flammable fluids near the stream of bypass air.
SUMMARY
[0003] In one aspect, there is provided a cooling system for a gas
turbine engine
comprising: a closed circuit containing a change-phase fluid, at least one
heat
exchanger configured to receive a first coolant from a first engine system for
the
change-phase fluid in the closed circuit to absorb heat from the first
coolant, whereby
the cooling system is configured so that the change-phase fluid at least
partially
vaporizes when absorbing heat from the at least one heat exchanger, and the
closed
circuit having a cooling exchanger adjacent to an annular wall of a bypass
duct, the
cooling exchanger configured to be exposed to a flow of cooling air in the
bypass duct
for the change-phase fluid to release heat to the cooling air and condense at
least
partially, the cooling exchanger having conduits configured to feed the
vaporized
change-phase fluid from a heat exchange with the at least one heat exchanger
to the
cooling exchanger, and to direct condensed change-phase fluid by gravity from
the
cooling exchanger to the at least one heat exchanger.
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[0004] In another aspect, there is provided a method for cooling at
least one
engine system of a gas turbine engine comprising: exposing a change-phase
fluid in a
closed circuit to a heat exchange with a coolant from at least one heat
exchanger of an
engine system to vaporize the change-phase fluid, directing the vaporized
change-
phase fluid to a cooling exchanger located in or around an annular wall of a
bypass duct
and exposed to a flow of cooling air in the bypass duct to condense the
vaporized
change-phase fluid, and directing condensed change-phase fluid by gravity to
the heat
exchange with the coolant of the at least one heat exchanger.
DESCRIPTION OF THE DRAWINGS
[0005] Reference is now made to the accompanying figures in which:
[0006] Fig. 1 is a schematic cross-sectional view of a gas turbine
engine;
[0007] Fig. 2 is a block diagram of a cooling system for a gas turbine
engine in
accordance with the present disclosure;
[0008] Fig. 3 is a schematic view of a vapour cycle for an embodiment
of the
cooling system of Fig. 2;
[0009] Fig. 4 is an enlarged view of a heat-absorption portion of an
embodiment of
the cooling system of Fig. 2;
[0010] Fig. 5 is a perspective view of an embodiment of the cooling
system of
Fig. 2 having a cooling exchanger in a bypass duct of the gas turbine engine;
[0011] Fig. 6 is a perspective view of part of the cooling system of
Fig. 5; and
[0012] Fig. 7 is a sectioned view of components of the cooling system
of Fig. 5.
DETAILED DESCRIPTION
[0013] Fig. 1 illustrates a gas turbine engine 10 of a type preferably
provided for
use in subsonic flight, generally comprising in serial flow communication a
fan 12
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through which ambient air is propelled, a compressor section 14 for
pressurizing the air,
a combustor 16 in which the compressed air is mixed with fuel and ignited for
generating an annular stream of hot combustion gases, and a turbine section 18
for
extracting energy from the combustion gases. The gas turbine engine 10 may
also
have a bypass duct defined by a bypass wall 19 among other surfaces. As is
known,
the gas turbine engine 10 may have different engine systems, such as an
auxiliary gear
box, and integrated drive generator that generate heat and hence may require
cooling.
Likewise, the gas turbine engine 10 may have an air cooled oil cooler used for
cooling
various engine systems, but the air cooled oil cooler must reject absorbed
heat.
[0014]
Referring to Fig. 2, a cooling system in accordance with the present
disclosure is generally shown at 20. The cooling system 20 is a closed circuit
type of
system, in that the fluid(s) it contains is(are) captive therein, with the
exception of
undesired leaks. Hence, the cooling system 20 is closed in that it allows heat
exchanges as desired, but generally prevents a transfer of mass or loss of
mass of the
fluid(s) it contains. The cooling system 20 includes a cooling fluid, selected
to be a
change-phase fluid. The cooling fluid may also be known as a coolant, as a
refrigerant,
etc. However, for simplicity and clarity, the expression "change-phase fluid"
will be
used, so as not to mix it up with the coolants used in closed circuits
associated with
engine systems, with which the change-phase fluid will be in a heat-exchange
relation.
The cooling fluid is said to be a change-phase fluid in that it changes phases
between
liquid and vapour in a vapour-condensation cycle, in such a way that it may
store latent
heat and efficiently absorb heat while remaining at a same temperature during
phase
change. Moreover, the change-phase fluid is known to have a greater density
when in
a liquid phase than in a vapour phase, which results in condensate to drip by
gravity
while vapour rises. According to an embodiment, the change-phase fluid is
water or
water-based, and may include other constituents, such as glycol, salts, etc.
Alternatively, other change-phase fluids, without water, may be used. In
an
embodiment, the change-phase fluid is non flammable. Hence, the change-phase
fluid
is in a gaseous and in a liquid state depending on the location in the cooling
system 20,
and the cooling system 20 may also include other fluids such as air.
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[0015] The cooling system 20 may have one or more reservoirs 21. The
reservoir
21 may be known as a receiver, a tank, etc. The reservoir 21 receives and
stores the
change-phase fluid, with the liquid state of the fluid in a bottom of the
reservoir 21.
According to an embodiment, a plurality of heat exchangers, illustrated as
22A, 22B and
22n (jointly referred to as 22) are also located in the reservoir 21, for
coolants
circulating in the heat exchangers 22 to be in a heat exchange relation with
the fluid in
the reservoir 21, i.e., in a non-mass transfer relation. Although shown
schematically in
Fig. 2, the heat exchangers 22 may have any appropriate configuration or
surface
component to enhance heat exchange, such as coils, fins, etc. Moreover,
although the
heat exchangers 22 are depicted as sharing a same reservoir 21, all or some of
the
heat exchangers 22 may have their own dedicated reservoir 21.
[0016] According to an embodiment, each heat exchanger 22 is associated
with an
own engine system. Stated different, each heat exchanger 22 is tasked with
releasing
heat from its related engine system. Hence, the heat exchangers 22 are also
part of
closed circuits, extending from the reservoir 21 to the engine system. The
engine
systems may include auxiliary gear box, and integrated drive generator. Also,
one of
the heat exchangers 22 may be part of an air cooled oil cooler. According to
an
embodiment, the heat exchangers 22 may be stacked one atop the other in the
reservoir 21, with the heat exchangers 22 all bathing in the liquid state of
the change-
phase fluid. Therefore, coolants circulating in any one of the heat exchangers
22 may
release heat to the change-phase fluid in the reservoir 21. Therefore, the
change-
phase fluid may boil, with vapour resulting from the heat absorption.
[0017] A pressure regulator 23 may be provided in one of the feed
conduits 24,
such as to regulate a pressure in the reservoir 21. The pressure regulator 23
may be
any appropriate device that operates to maintains a given regulated pressure
in the
reservoir 21, such that vapour exiting via the feed conduits 24 is above the
regulated
pressure. According to an embodiment, the pressure regulator 23 is a
sourceless
device, in that it is not powered by an external power source, and that is set
based on
the planned operation parameters of the gas turbine engine 10. For example,
the
pressure regulator 23 may be spring operated. Alternatively, the pressure
regulator 23
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may be a powered device, such as a solenoid valve, for instance with
associated
sensors or pressure detectors. Although not shown, complementary devices, such
as a
check valve, may be located in return conduits 25 directing condensate to the
reservoir
21. Fig. 2 shows a schematic configuration of the cooling system 20 with a
single feed
conduit 24 and single return conduit 25, but 24 and 25 may include networks of
conduits in any appropriate arrangements, for instance as shown in embodiments
described hereinafter.
[0018] The vaporized change-phase fluid is directed by the conduit(s)
24 to an
cooling exchanger 30 in which the cooling fluid will be exposed to a flow of
cooling air,
such that the vaporized fluid release its absorbed heat to the cooling air.
The cooling
exchanger 30 may be at any location in the gas turbine engine 10, and cooling
air may
be directed in any appropriate way to absorb heat from the cooling exchanger
30. As
described hereinafter, according to one embodiment, the cooling exchanger 30
is part
of the bypass duct, such that the cooling air is the bypass air. In rejecting
heat to the
cooling air, the cooling fluid may condensate. The conduits 25 are therefore
arranged
to direct the condensate to the reservoir 21. According to an embodiment, the
cooling
system 20 relies on vapour density to feed the cooling exchanger 30 and on
gravity for
the condensate to reach the reservoir 21, such that no motive force is
required to move
the cooling fluid, i.e., no powered device may be necessary. The vapour cycle
of the
change-phase fluid between heat absorption and heat release is generally shown
in
Fig. 3, in accordance with an embodiment. However, it is contemplated to
provide a
pump (such as one or more electric pumps) or like powered device to assist in
moving
the cooling fluid.
[0019] Referring to Fig. 4, there is shown an embodiment in which the
cooling
exchanger 30 is part of the bypass duct wall 19. The reservoir 21 is located
at a bottom
of the bypass duct wall 19, for condensate to flow to the reservoir 21 by the
effect of
gravity. The various heat exchangers 22 are shown as being stacked, with the
inlet
conduit and the outlet conduit pair of each heat exchanger 22 being adjacent
and on a
same side of the reservoir 21, although other arrangements are possible. The
feed
conduits 24 are located on an upper portion of the reservoir 21 to direct
vapour out of
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the reservoir 21, while the return conduits 25 are connected to a bottom
portion of the
reservoir 21 to feed condensate to the reservoir 21. By providing vapour and
fluid
connections at each end and on the sides of the reservoir 21 and stacking the
heat
exchangers 22 the effect of attitude and roll may be reduced.
[0020] Referring to Fig. 5, the bypass duct is shown in greater detail,
and may
include a forward wall portion 19A and a rear wall portion 19B. The cooling
system 20
may be located on the rear wall portion 19B, while the forward duct wall
portion 19A
may incorporate the access doors and mount points. According to an embodiment,
the
feed conduits 24 may include arcuate conduit segments 31 extend from straight
conduit
portions, to surround the bypass duct wall 19. As part of the network of
conduits 24, the
arcuate conduit segments 31 are tasked with directing vapour of the closed
circuit
toward a top of the bypass duct wall 19. Other shapes of conduit segments may
be
used, but the arcuate conduit segments 31 may appropriately be positioned in
close
proximity to the bypass duct wall 19. According to an embodiment, the ends of
the
arcuate conduit segments 31 are open at a top of the bypass duct wall 19, and
an
annular chamber is defined between the radially outer surface 19C of the
bypass duct
wall 19 and annular wall 19D sealingly mounted around the radially outer
surface 19C.
Therefore, vapor fed by the conduits 24 via the conduit segments 31 may fill
the annular
chamber. As the annular chamber is defined by the bypass duct wall 19, the
vapour will
be in heat exchange relation with the bypass duct wall 19. As the bypass duct
wall 19
is continuously cooled by a flow of bypass air, the vapour may condensate.
Hence, the
condensate will trickle down by gravity, and accumulate at a bottom of the
annular
chamber, to be directed to the reservoir 21.
[0021] Referring to Figs. 6 and 7, in accordance with another
embodiment, the
cooler exchanger 30 may include one or more annular headers 32 (i.e.,
manifolds,
annular conduits, etc). The annular headers 32 have an adaptor 33 at a top
end, the
adaptor 33 being for instance a tee-shaped adaptor 33 by which the top ends of
the
conduit segments 31 (Fig. 5) may be in fluid communication with the annular
headers
32 to feed same with vapour. The adaptors 33 define a passage by which vapour
is
then fed to the annular cavity 34 of the annular headers 32. A plurality of
pipes 35
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(a.k.a, conduits, tubes) may extend from between a pair of the annular headers
32, and
may be in fluid communication with the annular cavities 34 of the annular
headers 32,
such that the change-phase fluid may circulate freely therein. Therefore, as
vapour is
fed from the feed conduits 24 via the conduit segments 31, vapour reaches the
annular
headers 32 and flows into some of the pipes 35. The pipes 35 extend along the
bypass
duct wall 19, and may be in close proximity or conductive contact with it,
such that the
vapour circulating in the pipes 35 rejects heat to the bypass air by
convection and
conduction. Alternatively, the pipes 35 may define the annular surface of the
duct wall
19, so as to be directly exposed to the flow of bypass air. As the pipes 35
are cooled,
the vapour may condensate. As a result, the condensate flows down the pipes 35
to
one of the annular headers 32, for instance depending on the attitude of the
gas turbine
engine 10. The annular headers 32 are in fluid communication with the return
conduits
25. Hence, the inner surface of the pipes 35 is directly exposed to the bypass
flow.
[0022] In the embodiment of Figs. 6 and 7, the cooling system 20 uses
the duct 19
to be a large area cooler. The cooling system 20 may be constructed of a large
number of conduits 24 and 25 and the pipes 35 bent in the same shape and
subsequently stacked in a circular pattern and brazed to the headers 32 as a
single unit.
The headers 32 distribute the steam to the pipes 35 which are directly or
indirectly
exposed to the cooling air and cause the vapour to condense and flow to the
front or rear
headers 32 via gravity and back to the reservoir 21 located below the bypass
duct
cooler 30. The sequence is repeated on a continuous basis and is a sealed
system, due
to the closed nature of the circuit. The rejection of the heat to the bypass
air contributes
to the engine overall efficiency.
[0023] The cooling system 20 is of relatively low pressure and low
temperature
along with the possibility of employing a non flammable cooling fluid. As
observed from
Figs. 3 and 4, the reservoir 21 is centrally located, such that the oil and
change-phase fluid
routings are centrally located so as to be shorter. The centralizing may also
result in a
single area needing greater protection or shielding.
[0024] The cooling exchanger 30 of the cooling system 20 may be sized
as needed
for cooling. The majority of the heat to be rejected may come from sources
near the
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central location of the reservoir 21, which may results in short tube/hose
runs and
minimizes the hidden oil in the system. The cooling exchanger 30, when located
in or
defining the bypass duct wall 19 may be structural and therefore be capable of
sustaining both the mount and the thrust reverser loads.
[0025] According to an embodiment, the bypass duct has an aerodynamic
profile.
The pipes 35 may be bent in a pattern that forms an angle to the centreline of
the
engine which allows the duct of pipes 35 to be shaped to the required
aerodynamic
profile. The changing angle of the pipes 35 relative to the centreline of the
engine
produces a change in the duct diameter by virtue of the changing length in
response to
the angle. The assembly may be brazed as a unit. Tube diameter may be
relatively
large (for example, 0.5" diameter) with a thin wall (<0.010"). Although other
arrangements are considered, such a combination produces a stiff structure
with low
weight and a large wetted surface area.
[0026] As an example of operation of the cooling system 20, the
approximate heat
values in a ¨15,000 lb thrust turbofan engine are typically <1000 Btu/min for
the
integrated drive generator and <2000 Btu/min for the air cooled oil cooler,
¨5000
Btu/min for the buffer air cooler. The heat of vaporization of water is 970
Btu/lb which in
the present example would require ¨8 lb of water/glycol mix (an example of
change-
phase fluid) provided the vapour could be condensed efficiently enough to
refill the
reservoir 21. A benefit is the automatic compensation for differential heat
from the
various engine systems. In an example, the various heat exchangers 22 share
the
same reservoir 21 and respond to each heat exchanger 22 as its own system. If
one
system has increased heat influx, the steam generated flows into the cooling
exchanger
30 and condenses on the relative cool bypass duct wall 19 and the condensate
flows
back to the reservoir 21 as fluid and repeats the cycle again. Since the
cooling system
20 is a closed system, its pressure can be set through the pressure regulator
23, with
the trigger point adjusted to the lowest system temperature. An example, the
integrated
drive generator may have a specified maximum temperature of 185 F. By lowering
the
pressure in the reservoir 21 via the pressure regulator 23, the boiling point
of the
change-phase fluid can be adjusted to the required temperature. The other heat
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exchangers 22 in the reservoir 21 will be cooled to this temperature, which is
permissible because of the large condensing area of the cooling exchanger 19.
In this
manner, the cooling system 20 self regulates both the temperature and thermal
loads
between multiple engine systems, optionally without motive forces, powered
valves or
powered controls, eliminating such potential failure points.
[0027]
The above description is meant to be exemplary only, and one skilled in the
art will recognize that changes may be made to the embodiments described
without
departing from the scope of the invention disclosed. Still other modifications
which fall
within the scope of the present invention will be apparent to those skilled in
the art, in
light of a review of this disclosure, and such modifications are intended to
fall within the
appended claims.
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