Patent Application
20120168115
This patent application claims the benefit of European Patent Application No. 10197456.6, filed Dec. 31, 2010, the entire teachings and disclosure of which are incorporated herein by reference thereto.
The present invention relates to a heat-exchanger in aeronautics. It more particularly relates to a surface heat-exchanger whose heat transfers can be modulated depending on the usage phases of the airplane on the ground and during flight, respectively.
It also relates to a surface heat-exchanger provided with means for deicing part of the airplane.
The present invention also relates to an airplane engine comprising such a heat-exchanger.
In a turbomachine, different members and pieces of equipment (bearing enclosures, gearboxes, electrical machines, etc.) must be lubricated and/or cooled, the generated heat generally being transported by oil systems and evacuated by fuel-cooled oil and/or air-cooled oil coolers.
Current engines create a growing number of calories due to the increasing loading of the bearing enclosures, the integration of high-power gearboxes (turboprop, open rotor, etc.), and the integration of new pieces of equipment (high-power starter generator, etc.). As a result, the fuel-cooled oil coolers (FCOC) are saturated and require a supplement in the form of air-cooled oil coolers (ACOC).
Several types of air-cooled oil coolers exist. There are the brick-type exchangers. These are fairly heavy exchangers that have the drawback of disrupting the air flow and therefore penalizing the global output (increase in specific fuel consumption, SFC). In fact, for brick-type exchangers, the air is supplied by a system of ducts that cause increased drag or by a bleed system of the engine air flow that causes an aerodynamic disruption in the flow. Brick-type exchangers do, however, have the advantage that the air flow can be controlled with a rate generator (blower) and/or a rate limiter (flapper) depending on the usage phase of the airplane. This allows to limit the mass and the SFC (specific fuel consumption) impact of this technology, which is fundamentally heavy and intrusive in the flow, as the rate generator allows to decrease the size of the exchanger and the rate limiter decreases the SFC impact in cases where the exchanger is not necessary.
So-called surface exchangers also exist, the interest of which is that they cause less disruption in the aerodynamic flow. In the latter, an air flow is brought onto an exchange surface secured to the oil circuit. The exchanger may assume the form of a plate having fins on one side passed through by the air flow and, on another side, oil channels. These surface exchangers are intrinsically lighter and less intrusive, but they are not provided with regulation means, unlike brick-type exchangers. Furthermore, although they are less intrusive, their integration into the turbomachine nevertheless poses the following problems:
In the state of the art, EP 2 075 194 A1 is known, which presents a surface air-cooled oil cooler where the oil circuit is positioned inside the separator nose (i.e. the nose separating the air flows coming from the fan in a dual-flow turbomachine) and where the fins are positioned outside the upper wall of the separator nose. The positioning of the exchanger in the separator nose allows to deice the separator nose in addition to cooling the oil.
This surface exchanger also has the drawback that it is provided with no means for regulating the cooling airflow as a function of the usage conditions of the airplane (flight or ground).
As noted in application EP 2 075 194 A1, air-cooled oil coolers offer a heat source that could advantageously be used to deice stagnation points of the air flow, in particular that of the nacelle. Currently, the stagnation points (nacelle and separator nose) are deiced pneumatically by air bleed at the engine or electrically, which requires mechanical sampling causing losses of propulsive output in each case. Furthermore, the increasing use of organic composite materials to replace metal materials requires controlling the temperature inside the structures.
The present invention aims to provide a surface heat-exchanger provided with regulating means allowing to supply an airflow adapted to cooling needs.
The present invention also aims to supply a heat-exchanger whose integration within the turbomachine does not raise the aforementioned problems.
The present invention also aims to produce a heat-exchanger ensuring the deicing of the stagnation points of the air flow.
The present invention relates to a surface air-cooled oil cooler in an airplane engine comprising at least a first oil circuit and at least a first and second exchange surfaces positioned on either side of the first oil circuit and each able to be swept by an air flow, said second exchange surface being positioned in a cavity provided with an air inlet and an air outlet, said inlet and/or said outlet comprising covering means that allow to regulate the air supply on the second exchange surface.
According to specific embodiments of the invention, the surface air-cooled oil cooler comprises one or a suitable combination of the following features:
The present invention also relates to an airplane engine comprising an air-cooled oil cooler as described above.
The present invention consists in integrating a surface air-cooled liquid cooler into an airplane and, preferably, into the propulsion system (engine+nacelle). According to the invention, the surface exchanger is at least provided with two heat-exchange surfaces, one or both surfaces being swept by the cooling air, depending on the usage phases of the airplane on the ground or during flight. One of the two surfaces, which will be called first surface or outer surface, is exposed to an outside air flow independently of the usage phases of the airplane due to its positioning within the turbomachine, while the second surface is positioned in a cavity and is only exposed to an air flow in certain usage phases of the airplane. In this way, the air flow sweeping the second surface can be modulated owing to means for covering an air inlet and/or outlet of the cavity allowing a greater or lesser air passage, or no air passage at all, toward the inner surface. Preferably, the first surface is dimensioned for the usage phases of the airplane during flight (typically in cases beyond ground idle), while the second surface is only swept by the air and dimensioned to provide the additional cooling that is required during usage phases of the airplane on the ground. In general, the covering means are open when the heat exchange should be increased (in particular when the airspeed is low and, more particularly, at a low rating), while the covering means are closed when the airspeed is sufficient (in particular in cruising mode), the covering means being closed to limit the drag of the airplane.
The second exchange surface is provided with fins and the first exchange surface is provided with fins of reduced dimensions so as not to influence the aerodynamic performance. The latter can even be provided with no fins if the heat-exchange surface is large enough. According to the invention, the orientation angle and the technology of the fins are calculated in order to minimize weighting the SFC criteria and the mass is expressly chosen for each surface, as well as in order to optimize thermal performance.
The means for covering the air inlet and/or outlet can, for example, be a translation or rotation system. To generate a greater flow on the inner surface during low-speed phases, the exchanger may also be provided with a blower.
Still according to the invention, the heat coming from the exchanger is used to deice the nacelle or, more generally, the part of the airplane situated near the exchanger. In the case of nacelles made of a composite material, the deicing system is moreover provided with regulation means.
The surface exchanger as in the invention is illustrated below for embodiments where the exchanger comprises two oil circuits. The present invention also extends to other embodiments where the exchanger comprises only one oil circuit.
The exchanger 1 comprises a first 2 and a second exchange surfaces provided with fins. It also comprises a first 4 and a second 5 oil circuits and is provided with an air inlet 6 and outlet 7. The inlet 6 comprises covering means 8 such as a duct. The second exchange surface 3 and the second oil circuit 5 are positioned inside a cavity 9, while the first surface 2 is located outside the cavity 9. In the illustrated example, the duct opens toward the outside of the cavity and then forms a duct favoring the air inlet under its inner surface. Alternatively (not shown), the duct can open toward the inside of the cavity so as to keep a good air flow on the outer surface and minimize the aerodynamic impact thereof. As will be described below and illustrated in
In the example illustrated in
The covering means can assume intermediate positions (see view 2)) between a completely closed position (see view 1)) and a completely open position (see view 3)). In this way, when the airplane is on the ground in the start phase, the duct is either closed or open depending on the heat generation and on deicing needs. In 1), the scenario where the duct is closed during the ground start phase of the airplane is illustrated. The duct is also closed when the airplane is in cruising mode; the heat dissipation is then high because a large cold airflow sweeps the first surface. In 2), the airplane is in the MTO phase (max takeoff mode). In this usage phase of the airplane, the heat generation is significant and the cold air flow sweeping the first surface may not be enough to ensure sufficient dissipation. As a result, the duct is slightly or moderately open. In 3), the airplane is in ground idle mode. In that case, the natural heat exchange is limited because the cold airflow is very weak. Consequently, the duct is wide open and the blower is active to generate the flow. In the example illustrated in
According to the invention, the covering means may be actuated by an independent system such as an electric, electro-hydraulic, hydraulic or pneumatic system. The actuating system may be shared with other actuating systems not used at the same time (e.g. in the nacelle: reverse, etc.). Alternatively and as illustrated in
The second oil circuit 5 delimits a conduit 10 that channels the air flow created by the duct, optionally assisted by the blower 11. Alternatively (not shown), the exchanger may be provided without a second oil circuit with the result that the conduit for channeling the air flow is embodied by the exchanger on the one hand and by one wall of the cavity (for example of the nacelle) on the other hand. Still alternatively, the exchanger may be provided without a second oil circuit and may be provided with a ring positioned around the fins of the second surface in order to form a conduit and increase the exchange surface. According to the invention, a ring may also be positioned around the fins of the first surface with the same aim of increasing the exchange surface. The fins of the first surface or the ring surrounding the fins of the first surface can also benefit from a sound treatment in order to absorb the entire or part of the sound spectrum generated by the engine.
Ducts or covering means 8 are integrated between a first oil circuit 4 having a first exchange surface or outer surface 2 and a second oil circuit 5 having a second exchange surface or inner surface 3. Each duct is made up of a shroud or of shroud segments (generally, the duct fits the profile of the exchanger). This embodiment allows to integrate the actuating system of the ducts in the thermal exchanger on the operating principle of a piston. When the inlet and outlet ducts must close the cavity 9 as shown at the bottom of
As already mentioned, the inner surface of the surface exchanger as in the different embodiments of the invention must be positioned opposite a cavity or a conduit in the extension of the air-inlet cavity that may be passed through by an air flow when the air inlet and outlet of the cavity is not obstructed. For example, the exchanger as in the invention can be positioned at the level of the nacelle of the airplane. It may be positioned on the outer wall of the nacelle, i.e. the wall that is not opposite the fan. The first surface being positioned outside the cavity while the second surface is positioned inside the cavity of the nacelle. The exchanger can also be positioned on the inner wall of the nacelle upstream or downstream of the fan (the air flowing from upstream to downstream) and, more specifically, in the secondary stream in the latter case. It may also be positioned in the secondary flow on the outside of the separator separating the primary flow from the secondary flow of the engine. The configuration where the exchanger is positioned on the inner wall of the nacelle downstream of the fan has the advantage that the first surface is protected from FODs, is swept by an airflow of the fan as of start-up of the engine without the airplane being in motion, and does not constitute a burn risk for careless passengers.
Still according to the invention, the exchanger can be positioned continuously on the inner or outer wall of the nacelle or on the outside of the separator then forming a ring, or can be positioned in the form of a non-annular plate.
According to the invention and as already mentioned, the air-cooled oil cooler can be used to deice a surface that is subject to ice accretion. The heat can be transferred by direct contact (for example, by contact with the oil or even via a bleed forming a thermal bridge) if the surface of the exchanger is in contact with the surface to be deiced. The heat can also be transferred by natural convection, since the fins of the inner surface represent a heat-transfer source in the cavity when the latter is covered, and therefore allow to deice the surfaces in the immediate environment. Deicing can also be achieved by conduction via a thermal bridge, for example made via a metal blade. Lastly, deicing can also be achieved via a secondary circuit, for example of the diphasic-loop type.
The heat-exchanger as in the invention allows to regulate cooling of the oil while preserving the benefits related to the surface exchanger. In this way, the aerodynamic and acoustic impact of the exchanger is minimized as a result of the use of the surface technology, of the dimensioning of the outer surface for the “flight” cases with smaller fins, or even without fins, and of the closing of the inner portion for “flight” cases.
Owing to the use of the exchanger's thermal energy for deicing, it is no longer necessary to take energy from the engine, resulting in output gains.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10197456.6 | Dec 2010 | EP | regional |
