Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02647570 2008-12-22
HEAT EXCHANGE SYSTEM IN A TIIRBOMACHINL
Subject of the invention
[0001] The present invention relates to the field of
heat exchangers, preferably those intended for cooling
oil, for the lubrication system of an aircraft engine, in
particular a turbomachine.
State of the art
[0002] In a turbomachine, various units and
equipment must be lubricated and/or cooled, the heat
generated being usually carried by oil systems and
extracted by fuel/oil and/or air/oil exchangers. With each
unit or piece of equipment having its own specifications
regarding the lubrication, several oil systems may coexist
with their own structures, pressures, temperatures etc. In
the context of the current trend to "more electric" in
turbomachines, one might for example have a lubrication
system for the starter-generator (S/G) which is distinct
from the oil system for the engine's bearing chambers.
Where necessary, the calories generated in these two
systems must therefore be taken up by the oil which acts
as a liquid lubricant but also as a coolant fluid, in the
context of current engine development. The oil
requirements must therefore be increased in this
situation. Traditionally, according to the state of the
art, the lubrication and cooling circuits of electrical
equipment (S/Gs) are separate from the turbomachine
circuit, each having its own circulation system, which is
generally based on volumetric pumps, and its own cooling
system such as an air/oil and/or fuel/oil exchanger
("radiator").
[0003] The heat exchanger for each circuit is sized
for its critical point in the flight which depends on the
- 1 -
CA 02647570 2008-12-22
profile of heat generation of the machine to be cooled and
on the availability of the cold source as well as the
possible use of another cold source.
[0004] This therefore entails the following negative
effects:
- Oversizing of the equipment for all the other cases,
hence the considerable weight of the equipment;
- Oversizing of the equipment for all the other cases,
hence a useless disturbance of the airflow and more
generally a loss of output by the turbomachine, in the
case of an exchange with air;
- Overcooling of the oil in all the other cases, which
requires additional control equipment.
[0005] The sizing parameters being different for the
two present circuits, the sizing points of the exchanger
of each circuit are thus also different.
[0006] Document GB-A-2 052 722 discloses a multiple
fluid heat exchanger, for use as a radiator for the
coolant system of an internal combustion engine in
automotive vehicles, comprising a first liquid-to-liquid
cooler of the stacked plate type (e.g. water/motor oil
cooler) and a second liquid-to-liquid cooler of the
stacked plate type (e.g. water/transmission oil cooler).
The two liquid-to-liquid coolers are separated by a baffle
preventing thermal exchange between them. Thus the coolant
(water) is used to separately cool at least two hot fluids
(e.g. motor oil and transmission oil), successively or in
parallel. Corrugated heat exchange fins may be provided in
the coolant passage so that to cool the coolant further,
e.g. with air.
- 2 -
CA 02647570 2008-12-22
Aims of the invention
[0007] The present invention aims to provide a
solution which will allow the disadvantages of the state
of the art to be overcome.
5[0008] In particular, the invention aims to propose
a cooling system which avoids any oversizing of the
individual heat exchangers associated with two or more
cooling structures in a turbomachine.
[0009] In particular, the invention also aims to
reduce the weight of this equipment as well as the useless
intake of air.
[0010] The invention also aims to eliminate the need
for supplementary control equipment by means of the
simplification of the cooling system.
Main characteristic elements of the invention
[0011] A first subject of the present invention
relates to a heat exchange system in a turbomachine
comprising a number of units and equipment to be cooled
and/or lubricated, said system comprising at least two
distinct oil circuits for cooling and/or lubricating said
equipment, characterised in that said system is configured
to put said oil circuits in thermal contact with each
other on the one hand and with a fluid playing the part of
a cold source on the other hand.
[0012] According to a preferred embodiment of the
invention, the exchanger comprises a fluid/oil exchange
element which is common to both oil circuits.
[0013] Said common exchange element preferably
comprises a plate incorporating each of said oil circuits
and which exchanges heat with the fluid of one single
external side of the plate or both.
[0014] As a further preference, the external side or
sides of the plate used for the heat exchange between the
- 3 -
CA 02647570 2008-12-22
oil circuits and said fluid, is/are in the form of,
equipped with or surmounted by fins.
[0015] According to a first preferred embodiment,
the common exchange element is of a surface type, that is,
it consists of a single plate designed to be incorporated
along an existing surface.
[0016] According to a second preferred embodiment,
the exchange element common to the two oil circuits is of
a "sandwich" type, that is, comprising a stack of several
plates containing the individual oil circuits separated by
fins between which the fluid circulates.
[0017] According to these embodiments, the circuits
are preferably entangled in each plate.
[0018] As a further alternative, the plate is
separated into two parts by a partition where the fluid
circulates and where its nature and thickness are selected
so as to regulate the thermal interaction.
[0019] The partition is preferably equipped with
fins.
[0020] As an advantage, the heat exchanger fluid is
the external air or a fuel.
[0021] According to an alternative embodiment of the
invention, the heat exchange system contains a fluid/oil
exchange element which is common to both oil circuits,
comprising one or more tube(s) and a chamber.
[0022] According to a first embodiment, at least one
first tube comprises the first oil circuit and at least a
second tube comprises the second oil circuit, all the
tubes soaking in the fluid playing the part of the cold
source and circulating in the chamber. In this case, the
latter is the air or, preferably, the engine's fuel.
[0023] According to a second embodiment, the tube or
tubes on the one hand carry the fluid and on the other
hand soak in the chamber, a first compartment of which is
- 4 -
i . . . . . . . . . . . . .
CA 02647570 2008-12-22
a part of the first oil circuit and a second compartment
is a part of the second oil circuit.
[0024] Still according to the invention, as an
advantage, each individual oil circuit also comprises, as
well as the common exchange element, its own means of heat
exchange.
[0025] As an advantage, the common exchange element
may be located either upstream or downstream from said
means of heat exchange relative to the units and equipment
to be cooled and/or lubricated.
[0026] A second subject of the present invention
relates to a lubrication and/or cooling system for a
turbomachine comprising a heat exchange system according
to the features mentioned above.
[0027] As an advantage, the first lubrication
circuit feeds the engine circuit of the turbomachine and
the second lubrication circuit feeds an electric starter-
generator (S/G).
[00281 A third subject of the present invention
relates to a turbomachine comprising the above-mentioned
lubrication and/or cooling system.
Brief description of the diagrams
[00291 Diagram 1 shows a schematic view of an
air/oil heat exchanger 4 which is common to two cooling
systems 2,3, that of the engine itself and that of the
S/G, in a turbomachine, according to the present
invention.
[0030] Diagram 2 shows a schematic view of a first
preferred embodiment of the present invention where two
oil circuits are arranged in a plate which exchanges heat
with the ambient air or the fuel.
[0031] Diagram 3 shows a schematic view of a second
preferred embodiment of the present invention where two
- 5 -
CA 02647570 2008-12-22
oil circuits are arranged in a plate which exchanges heat
with the ambient air or the fuel.
[0032] Diagram 4 shows a third preferred embodiment
of the present invention, where the exchange plate is
divided into two parts, the thermal interaction being
regulated by the nature and thickness of the separation
between the two sections.
[0033] Diagrams 5A and 5B show alternative
embodiments of the invention, where the heat exchanger
comprises a fluid/oil exchange element of the "tubes and
chamber" type.
Description of a preferred embodiment of the invention
[0034] The invention consists in combining the
functions of heat (or "calorie") extraction of two or more
systems or oil circuits 2,3 in a turbomachine into a
single, common heat exchanger 4. The sizing of the
exchangers of the two circuits 2,3 being in principle made
for different flight situations, the use of a common
equipment 4 to perform both functions allows to reduce the
oversizing as well as its disadvantages in all other
flight situations.
[0035] This equipment is primarily used for cooling the
two oils whilst generating a thermal interaction with a
beneficial effect between the two systems. It does not
have to be the only means of extracting the heat for the
two oil circuits 2,3, which may each contain its own
individual means of cooling 2A,3A (see Diagram 1).
[0036] The design will be developed according to the
degree of interaction desired between the thermal
behaviour of the two oil systems. The overall cooling of
both oil systems is ensured by the air or by fuel and the
interaction between the two oils allows to regulate their
temperatures across all engine speeds, wherein an oil can
- 6 -
CA 02647570 2008-12-22
be used to provide either supplementary cooling or heating
(in the case of an overcooled oil) to the other oil. There
is therefore a self-regulation between the two oils by
means of a passive component (common radiator), where the
respective roles of the two oils can be reversed from one
engine speed to another.
[0037] The solution proposed according to a first
preferred embodiment of the invention may be implemented
either in an exchange element or surface ACOC (stands for
Air Cooled Oil Cooler) 4, comprising a single plate 5 with
an oil circuit exchanging heat with the air of one single
external side or both, the latter being preferably
equipped with fins 6, or in an ACOC of an either
"sandwich" or "plates and fins" type, comprising a stack
of plates 5 with oil circuits separated by fins 6 where
the air (not shown) circulates. The arrangement of the two
oil circuits into each plate will depend on the degree of
thermal interaction desired between the two oils.
[0038] According to another preferred embodiment,
the two circuits will be more or less heavily entangled in
a single plate (see Diagrams 2 and 3). According to yet
another preferred embodiment, one or more of the plates 5,
shown in Diagrams 2 and 3, will be separated into two
parts 5A, 5B, the thermal interaction between the two
respective oils being regulated by the nature and
thickness of a separating partition 7, which is preferably
equipped with fins 6 (see Diagram 4).
[0039] Alternative embodiments of the invention are
shown in Diagrams 5A and 5B respectively (exchanger of the
"tubes and chamber" type). In Diagram 5A, the first oil
circuit 2 and the second oil circuit 3 have the form of
tubes soaked in a chamber 8, in which the fluid that plays
the part of the cold source circulates. Said fluid is
preferably the engine's fuel. In Diagram 5B, the tube or
- 7 -
CA 02647570 2008-12-22
tubes 9 carry the fluid (fuel) and soak in a chamber
comprising on the one hand a compartment being a part of
the first oil circuit 2 and on the other hand a
compartment being a part of the second oil circuit 3, both
isolated from each other. The multi-fluid heat exchanger
proposed in document GB A-2 052 722 combines several
classical exchangers next to each other. There is for
example a first coolant fluid/hot fluid exchanger A
followed by a second coolant fluid/hot fluid exchanger B.
Unlike the present invention, the oil circuits are not
entangled, which means they cannot exchange heat between
each other. The two hot fluids are systematically cooled
one after the other or one at the same time as the other
by the coolant fluid.
Advantages of the invention
- Combination of the cooling of the two different oils in
a single ACOC element, allowing to avoid the presence of
two cooling structures and therefore to save weight and
bulk, in particular with regard to the fixings and
connections;
- Possible control of the thermal interaction between the
two lubrication circuits through the design of the
exchanger. By using a first oil to cool the second oil
when the engine is running, the need for interaction
with the airflow is reduced, as is therefore possibly
the disturbance of the airflow. This solution also
allows to avoid a possible overcooling at high engine
speed, the overcooled oil taking calories from the
hotter oil;
- Output of the heat exchange between two hydraulic fluids
better than that of oil/air exchange (in the case of an
- 8 -
CA 02647570 2008-12-22
ACOC), even if ultimately the overall exchange will be
made with the external air.
- 9 -
