Patent Application
20090159246
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.
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”).
The heat exchanger for each circuit is sized for its critical point in the flight which depends on the 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.
This therefore entails the following negative effects:
The sizing parameters being different for the two present circuits, the sizing points of the exchanger of each circuit are thus also different.
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.
The present invention aims to provide a solution which will allow the disadvantages of the state of the art to be overcome.
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.
In particular, the invention also aims to reduce the weight of this equipment as well as the useless intake of air.
The invention also aims to eliminate the need for supplementary control equipment by means of the simplification of the cooling system.
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.
According to a preferred embodiment of the invention, the exchanger comprises a fluid/oil exchange element which is common to both oil circuits.
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.
As a further preference, the external side or sides of the plate used for the heat exchange between the oil circuits and said fluid, is/are in the form of, equipped with or surmounted by fins.
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.
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.
According to these embodiments, the circuits are preferably entangled in each plate.
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.
The partition is preferably equipped with fins.
As an advantage, the heat exchanger fluid is the external air or a fuel.
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.
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.
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 a part of the first oil circuit and a second compartment is a part of the second oil circuit.
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.
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.
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.
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).
A third subject of the present invention relates to a turbomachine comprising the above-mentioned lubrication and/or cooling system.
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.
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.
Diagram 3 shows a schematic view of a second 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.
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.
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.
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.
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).
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 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.
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.
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).
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 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP07447069.1 | Dec 2007 | EP | regional |
