Abstract:
A system for cooling a heat exchanger on board an aircraft includes an engine bleed air line connected to an engine of the aircraft and adapted to supply engine bleed air to the heat exchanger. The system further includes a process air line branching off from the engine bleed air line such that the engine bleed air is supplied to the process air line and connecting to an input side of a turbine. The system also includes a cooling air line connected to an output side of the turbine such that cooling air produced by an expansion of the engine bleed air supplied to the turbine is supplied to the cooling air line and then to the heat exchanger. The heat exchanger is adapted to transfer cooling energy from the cooling air to the engine bleed air supplied to the heat exchanger from the engine bleed air line.

Description:
This application claims priority under Section 371 and/or as a continuation under Section 120 to PCT Application No. PCT/EP2009/007647, filed on Oct. 26, 2009, which claims priority to German Application No. 10 2008 055 888.5 and U.S. Provisional Application No. 61/111,375, both filed on Nov. 5, 2008. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a system for cooling a heat exchanger on board an aircraft. 
     BACKGROUND 
     In modern commercial aircraft heat exchangers are installed in various systems, such as for example an aircraft air conditioning system, a de-icing system or cooling system for cooling thermally loaded equipment on board the aircraft. Depending on requirements, the heat exchangers may take the form of gas-gas heat exchangers, gas-liquid heat exchangers or liquid-liquid heat exchangers. Heat exchangers that are used to cool hot bleed air removed from the engine compressors or auxiliary engine compressors for further use in the aircraft air conditioning system or the de-icing system of the aircraft are currently cooled by engine cooling air removed from the engine, so-called “fan air”. Alternatively, the heat exchangers, through which hot engine bleed air flows, may also be cooled by ambient air that flows through a cooling air duct. In order to convey the ambient air through the cooling air duct, hot engine bleed air may be directed via an injector nozzle into the cooling air duct. The jet pump effect produced by the injection of engine bleed air into the cooling air duct then ensures that sufficient ambient air is sucked into the cooling air duct and through the heat exchanger that is to be cooled. 
     Particularly in aircraft that are equipped with propeller engines there is the problem that no engine cooling air may be removed from the engines. The cooling of a heat exchanger, through which hot engine bleed air flows, then inevitably requires the use of a cooling duct, into which hot engine bleed air is injected through an injector nozzle in order to convey ambient air through the cooling air duct and through the heat exchanger that is to be cooled. The injection of highly compressed engine bleed air into a cooling duct may however lead to considerable noise emissions because of the expansion of the engine bleed air in the cooling duct. Furthermore, the removal of large quantities of heat from the heat exchanger, through which hot engine bleed air flows, requires a high cooling air-mass flow, which may be conveyed through the cooling duct only by the injection of a correspondingly high injection air-mass flow into the cooling duct. Finally, a cooling system, in which ambient air is conveyed through a cooling duct by the injection of engine bleed air into the cooling duct, has the drawback that the engine bleed air is utilized, not directly, but only indirectly for cooling purposes. This leads to losses in the energy efficiency of the system. 
     The invention is geared to the object of indicating a system for cooling a heat exchanger on board an aircraft that may be operated in an energy-efficient manner without the use of engine cooling air. 
     SUMMARY 
     To achieve this object, a system according to the invention for cooling a heat exchanger on board an aircraft comprises a process air line, a first end of which is connected to an engine of the aircraft in order to supply engine bleed air, i.e. air at an elevated pressure and at an elevated temperature, to the process air line. A second end of the process air line is connected to an input side of a turbine in order to supply the engine bleed air flowing through the process air line to the turbine. In the turbine the engine bleed air under elevated pressure is expanded and at the same time undergoes cooling. A first end of a cooling air line is therefore connected to an output side of the turbine in order to supply the cooling air line with cooling air that is produced by expansion of the engine bleed air in the turbine. The cooling air line is further adapted to supply the cooling air flowing through the cooling air line to the heat exchanger that is to be cooled. The cooling air line may be coupled in any desired manner thermally to the heat exchanger. The important point is merely that a proper transfer of cooling energy from the cooling air flowing through the cooling air line to the heat exchanger that is to be cooled is guaranteed. For example, the cooling air line may extend in a suitable form through the heat exchanger. The heat exchanger to be cooled may be a single heat exchanger or a multiple heat exchanger. 
     The cooling system according to the invention enables proper cooling of the heat exchanger provided on board the aircraft both during taxiing and cruising of the aircraft without the use of engine cooling air. The cooling system is therefore freely usable also in aircraft, which are equipped with propeller engines and in which it is not possible to tap engine cooling air. The cooling system is moreover operable with relatively low noise, with the result that the use of sound-insulating material, such as is necessary in the cooling systems of prior art, in which ambient air is conveyed through a cooling duct by the injection of engine bleed air into the cooling duct, may be avoided. This enables savings in cost and weight. A further advantage of the cooling system according to the invention is its simple construction. The cooling system may therefore, if necessary, be integrated in a relatively simple manner into a primary cooling system. Finally, the cooling system according to the invention takes up only relatively little installation space. 
     The process air line of the cooling system according to the invention may be connected directly to the engine of the aircraft. Alternatively, the process air line may however be connected by a further line or further lines or other components to the engine of the aircraft. For example, the process air line may branch off from an engine bleed air line, a first end of which is connected to the engine of the aircraft in order to supply engine bleed air to the engine bleed air line. The engine bleed air line may supply engine bleed air to other systems on board the aircraft, such as for example the aircraft air conditioning system or a de-icing system of the aircraft. Should this be necessary for further utilization of the engine bleed air for example in the previously mentioned aircraft systems, the engine bleed air line may supply the engine bleed air flowing through the engine bleed air line to a suitable cooling device. For example, the engine bleed air line may be adapted to convey the engine bleed air flowing through the engine bleed air line through the heat exchanger that is cooled by means of the cooling system according to the invention. 
     The process air line may branch off from the engine bleed air line, in relation to the direction of flow of the engine bleed air through the engine bleed air line, upstream of the heat exchanger to be cooled. Given such an arrangement, the engine bleed air may be supplied to the process air line and subsequently to the turbine without pressure- and temperature losses. However, should this be desirable or necessary, the process air line may branch off from the engine bleed air line, in relation to the direction of flow of the engine bleed air through the engine bleed air line, alternatively downstream of the heat exchanger. 
     The heat exchanger to be cooled may be cooled exclusively by means of the cooling air flowing through the cooling air line. However, the heat exchanger to be cooled may alternatively be disposed in a cooling duct, through which ambient air may flow. The cooling duct may be configured for example in the form of a ram-air duct. During cruising of the aircraft the heat exchanger may then be cooled by means of ambient air flowing through the cooling duct, whereas during taxiing of the aircraft cooling of the heat exchanger is possible by means of the cooling air flowing through the cooling air line. Given such an arrangement, at least during cruising of the aircraft a simultaneous cooling of the heat exchanger by means of ambient air and cooling air from the cooling air line may further be effected. In this way the cooling capacity of the cooling system according to the invention may be increased. Depending on the style of construction of the heat exchanger, the ambient air flowing through the cooling duct and the cooling air from the cooling air line may be conveyed as separate air flows through the heat exchanger. It is however alternatively conceivable to combine the ambient air flowing through the cooling duct and the cooling air from the cooling air line into a single air flow upstream or downstream of the heat exchanger. Such a development of the cooling system according to the invention may be realized for example by means of a cooling air line that opens into the cooling duct. 
     The system according to the invention for cooling a heat exchanger on board an aircraft preferably further comprises a compressor, which is driven by the turbine and adapted to take in and compress ambient air. For example, the turbine and the compressor may be configured in the form of a compressor/turbine unit and be disposed on a common shaft. The ambient air taken in and compressed by the compressor may be returned unused into the environment. Preferably, however, the compressed air produced by the compressor is supplied for further use. For example, the compressed air produced by the compressor may be supplied to other aircraft systems, such as for example the aircraft air conditioning system. An alternative or additional possibility is however the use of the compressed air produced by the compressor in the cooling system according to the invention. 
     For example, an input side of the compressor may be connected to an ambient air line in order to convey ambient air into the ambient air line, wherein the ambient air line may be adapted to supply the ambient air flowing through the ambient air line to the heat exchanger that is to be cooled. In other words, the compressor may be used to supply cooling ambient air, in addition to the cooling air from the cooling air line, to the heat exchanger. In this way, not only the cooling capacity but also the energy efficiency of the cooling system may be increased. The ambient air line may be coupled in any desired manner thermally to the heat exchanger. The important point is merely that a proper transfer of cooling energy from the ambient air flowing through the ambient air line to the heat exchanger that is to be cooled is guaranteed. 
     If the heat exchanger to be cooled is disposed in a cooling duct, through which ambient air may flow, the input side of the compressor may also be connected to the cooling duct in order to convey ambient air through the cooling duct. In other words, the ambient air line that is connected to the input side of the compressor may be formed partially or entirely by the cooling duct. It is alternatively conceivable to fashion the ambient air line and the cooling duct in such a way that the ambient air line or a portion of the ambient air line opens into the cooling duct, so that ambient air sucked from the environment through the ambient air line may be fed into the cooling duct. 
     In an alternative development of the cooling system according to the invention, an output side of the compressor is connected to a compressor air line in order to supply compressed compressor air to the compressor air line, wherein the compressor air line is adapted to supply the compressor air flowing through the compressor air line to the heat exchanger that is to be cooled. In this development of the cooling system according to the invention too, the compressor is used to supply additional cooling air to the heat exchanger. Thus, this form of implementation of the cooling system also allows an increase of the cooling capacity and the energy efficiency of the system. The compressor air line may be coupled in any desired manner thermally to the heat exchanger. The important point is merely that a proper transfer of cooling energy from the compressor air flowing through the compressor air line to the heat exchanger that is to be cooled is guaranteed. 
     The compressor air line may extend in the form of a separate line through the heat exchanger that is to be cooled. However, the compressor air line may alternatively open out into the cooling air line so that the compressor air flowing through the compressor air line and the cooling air flowing through the cooling air line may be directed in the form of a single air flow through the heat exchanger. If the heat exchanger is disposed in a cooling duct, through which ambient air may flow, the compressor air line or a portion of the compressor air line may also open into the cooling duct. Furthermore, the output side of the compressor may be connected directly to the cooling duct, so that the compressor air line may be formed partially or entirely by the cooling duct. Finally, the compressor may also be integrated into the cooling duct. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred forms of implementation of the system according to the invention for cooling a heat exchanger on board an aircraft are described in detail below with reference to the accompanying diagrammatic drawings, which show: 
         FIG. 1  a first form of implementation of a system for cooling a heat exchanger on board an aircraft, 
         FIG. 2  a second form of implementation of a system for cooling a heat exchanger on board an aircraft, 
         FIG. 3  a third form of implementation of a system for cooling a heat exchanger on board an aircraft, 
         FIG. 4  a fourth form of implementation of a system for cooling a heat exchanger on board an aircraft, 
         FIG. 5  a fifth form of implementation of a system for cooling a heat exchanger on board an aircraft, 
         FIG. 6  a sixth form of implementation of a system for cooling a heat exchanger on board an aircraft, 
         FIG. 7  a seventh form of implementation of a system for cooling a heat exchanger on board an aircraft and 
         FIG. 8  an eighth form of implementation of a system for cooling a heat exchanger on board an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     A cooling system denoted by  10  in  FIG. 1  is used to supply cooling energy to a heat exchanger  12  on board an aircraft. The heat exchanger  12  may take the form of a single- or multiple heat exchanger and through it flows hot engine bleed air, which is supplied to the heat exchanger  12  by an engine bleed air line  14 . At its first end the engine bleed air line  14  comprises two engine bleed air line branches  14   a ,  14   b . The engine bleed air line branches  14   a ,  14   b  are connected at different positions to an engine  16  of the aircraft. Hot engine bleed air removed from the engine  16  therefore flows through the engine bleed air line branches  14   a ,  14   b  into the engine bleed air line  14  and, from there, through the heat exchanger  12 . After flowing through the heat exchanger  12 , the engine bleed air is supplied to an aircraft air conditioning system (not shown in detail) and to a wing de-icing system (likewise not represented) of the aircraft. 
     The engine bleed air flowing through the engine bleed air line branch  14   b  has a higher system pressure than the engine bleed air that is removed from the engine  16  of the aircraft through the engine bleed air line branch  14   a . In order to prevent the engine bleed air that is under a higher pressure from flowing out of the engine bleed air line branch  14   b  through the engine bleed air line branch  14   a  and back into the engine  16 , a check valve  18  is disposed in the engine bleed air line branch  14   a . The engine bleed air flow through the engine bleed air line branch  14   b , on the other hand, is controlled by a control valve  20 . Further control valves  22 ,  24  control the flow of the engine bleed air through the engine bleed air line  14  between a connection point of the engine bleed air line branches  14   a ,  14   b  and the heat exchanger  12 . Finally, a further control valve  26  is disposed downstream of the heat exchanger  12  in the engine bleed air line  14  and controls the supply of engine bleed air into the aircraft air conditioning system and the wing de-icing system of the aircraft. 
     Upstream of the heat exchanger  12  a process air line  28  branches off from the engine bleed air line  14 . A first end of the process air line  28  that is connected to the engine bleed air line  14  is therefore connected by the engine bleed air line  14  and the engine bleed air line branches  14   a ,  14   b  to the engine  16  of the aircraft, so that hot engine bleed air removed from the engine  16  flows through the process air line  28 , just as it does through the engine bleed air line  14 . A second end of the process air line  28  is connected to an input side of a turbine  30 , so that hot, highly compressed engine bleed air is supplied through the process air line  28  to the turbine  30 . Control of the engine bleed air flow through the process air line  28  is effected by means of a control valve  32 , which is disposed upstream of the turbine  30  in the process air line  28 . 
     The hot, highly compressed engine bleed air, as it flows through the turbine  30 , is expanded and at the same time undergoes cooling. The expanded cooled engine bleed air is supplied as cooling air to a cooling air line  34 , a first end of which is connected to an output side of the turbine  30 . The cooling air line  34  in its further course is coupled thermally to the heat exchanger  12 , so that the cooling energy of the cooling air flowing through the cooling air line  34  may be used to cool the heat exchanger  12 . The thermal coupling between the cooling air line  34  and the heat exchanger  12  may be established in any desired suitable manner. For example, the cooling air line  34  may extend through the heat exchanger  12 . Control of the cooling air flow through the cooling air line  34  between the output side of the turbine  30  and the heat exchanger  12  is effected with the aid of a control valve  36 . 
     Downstream of the heat exchanger  12 , i.e. after the cooling air flowing through the cooling air line  34  has transferred its cooling energy to the heat exchanger, i.e. to the hot engine bleed air from the engine bleed air line  14  flowing through the heat exchanger  12 , the cooling air flowing through the cooling air line  34  is released into the environment. The release of cooling air into the environment is controlled with the aid of a control valve  38 , which is disposed downstream of the heat exchanger  12  in the cooling air line  34 . 
     The energy generated by the expansion of the hot, highly compressed engine bleed air in the turbine  30  is used to drive a compressor  40 , which with the turbine  30  forms a compressor/turbine unit and is disposed with the turbine  30  on a common shaft  42 . An input side of the compressor  40  is connected to an ambient air line  44 , so that the compressor  40  during operation draws in ambient air through the ambient air line  44 . In the compressor  40  the ambient air is compressed. An output side of the compressor  40  is connected to a compressor air line  46 . The compressed compressor air flowing through the compressor air line  46  may be released unused into the environment. Alternatively, the compressor air from the compressor air line  46  may however be supplied to another system of the aircraft, for example to the aircraft air conditioning system or to another system that requires compressor air. Control of the ambient air flow through the ambient air line  44  is effected by means of a control valve  48 , which is disposed in the ambient air line  44 . In order to control the compressor air flow through the compressor air line  46  a control valve  50  is disposed in the compressor air line  46 . 
     The cooling system  10  shown in  FIG. 2  differs from the arrangement represented in  FIG. 1  in that the heat exchanger  12  is disposed in a cooling duct  52 . Ambient air flows through the cooling duct  52 , which may be configured for example in the form of a ram-air duct. For controlling the ambient air flow through the cooling duct  52  a control valve  54  is provided. The control valve  54  may be configured for example in the form of a ram-air duct inlet flap. 
     During cruising of the aircraft, if the aircraft has a suitably high air speed, ambient air flows through the cooling duct  52  so that the heat exchanger  12  may be cooled exclusively by the cooling energy contained in the ambient air flowing through the cooling duct  52 . Alternatively, during cruising of the aircraft cooling of the heat exchanger  12  is however possible also by means of a combination of ambient air flowing through the cooling duct  52  and cooling air from the cooling air line  34 . Thus, during cruising of the aircraft by using the ambient air flowing through the cooling duct  52  and the cooling air from the cooling air line  34  to cool the heat exchanger  12  the cooling capacity of the system may be increased. If the heat exchanger  12  may also be cooled exclusively by means of the ambient air flowing through the cooling duct  52 , it is possible to dispense with the removal of engine bleed air through the process air line  28 . For this purpose, for example the control valve  32  may be closed. During taxiing of the aircraft, on the other hand, the cooling air from the cooling air line  34  ensures an adequate cooling of the heat exchanger  12 . 
     The ambient air flowing through the cooling duct  52  and the cooling air from the cooling air line  34  may be directed as separate air flows through the heat exchanger  12  or be brought in some other way into thermal contact with the heat exchanger  12 . The ambient air flowing through the cooling duct  52  and the cooling air from the cooling air line  34  may however alternatively be combined into a single air flow upstream or downstream of the heat exchanger. For this purpose, as is shown in  FIG. 2 , the cooling air line  34  may open out into the cooling duct  52 . Otherwise the construction and the mode of operation of the cooling system  10  shown in  FIG. 2  correspond to the construction and the mode of operation of the arrangement represented in  FIG. 1 . 
     The cooling system  10  shown in  FIG. 3  differs from the arrangement according to  FIG. 1  in that the process air line  28  branches off from the engine bleed air line  14 , not upstream, but downstream of the heat exchanger  12 . Otherwise the construction and the mode of operation of the cooling system  10  according to  FIG. 3  correspond to the construction and the mode of operation of the system represented in  FIG. 1 . 
     In a similar manner the cooling system  10  shown in  FIG. 4  differs from the system according to  FIG. 2  in that the process air line  28  branches off from the engine bleed air line  14 , not upstream, but downstream of the heat exchanger  12 . Otherwise the construction and the mode of operation of the cooling system  10  shown in  FIG. 4  correspond to the construction and the mode of operation of the arrangement according to  FIG. 2 . 
       FIG. 5  shows a cooling system  10  that differs from the system according to  FIG. 1  in that the ambient air line  44  connected to the input side of the compressor  40  is coupled thermally to the heat exchanger  12 . The cooling energy that is contained in the ambient air drawn through the ambient air line  44  by the compressor  40  may therefore be used to cool the heat exchanger  12 . The use of the output of the compressor  40  to provide additional cooling energy for the heat exchanger  12  makes it possible to increase of the cooling capacity of the cooling system  10  in an energy-efficient manner. For controlling the ambient air flow through the ambient air line  44  a further control valve  56  is provided in the ambient air line between the heat exchanger  12  and the input side of the compressor  40 . Otherwise, the construction and the mode of operation of the cooling system  10  shown in  FIG. 5  correspond to the construction and the mode of operation of the arrangement according to  FIG. 1 . 
       FIG. 6  shows a cooling system  10  that differs from the system according to  FIG. 5  in that the heat exchanger  12  is disposed in a cooling duct  52  and that the ambient air line  44 , through which the compressor  40  draws in ambient air, comprises a first portion  44   a  that opens out into the cooling duct  52  as well as a second portion  44   b  that connects the cooling duct  52  to the input side of the compressor  40 . The compressor  40  therefore draws in ambient air through the cooling duct  52 . Otherwise, the construction and the mode of operation of the cooling system  10  according to  FIG. 6  correspond to the construction and the mode of operation of the arrangement represented in  FIG. 5 . 
       FIG. 7  shows a cooling system  10  that differs from the system according to  FIG. 1  in that the compressor air line  46  connected to the output side of the compressor  40  is coupled thermally to the heat exchanger  12 . In other words, the compressor air line  46  supplies the compressed compressor air flowing through the compressor air line  46  for cooling purposes to the heat exchanger  12 . After flowing through the heat exchanger  12  the compressor air from the compressor air line  46 , like the cooling air from the cooling air line  34 , is released into the environment. For controlling the release of the compressor air from the compressor air line  46  a control valve  58  is provided. In the arrangement shown in  FIG. 7  the compressor air from the compressor air line  46  and the cooling air from the cooling air line  34  are directed as separate air flows through the heat exchanger  12  and released downstream of the heat exchanger  12  into the environment. Alternatively, the compressor air from the compressor air line  46  and the cooling air from the cooling air line  34  may be combined into a single air flow upstream or downstream of the heat exchanger  12 . Finally,  FIG. 8  shows a cooling system  10  that differs from the arrangement according to  FIG. 7  in that the heat exchanger  12  is disposed in a cooling duct  52 . The heat exchanger  12  may therefore be cooled by means of cooling air from the cooling air line  34 , compressor air from the compressor air line  46  and ambient air flowing through the cooling duct  52 . Control of the return of the ambient air flowing through the cooling duct  52  into the environment downstream of the heat exchanger  12  is effected by means of a control valve  60 . The cooling air from the cooling air line  34 , the compressor air from the compressor air line  46  and the ambient air flowing through the cooling air duct  52  may once more be directed as separate air flows through the heat exchanger  12 . However, some or all of the air flows may alternatively be combined into a single air flow upstream or downstream of the heat exchanger  12 . 
     The control valves  20  to  26 ,  32 ,  36 ,  37   38 ,  48 ,  50  and  54  to  58  may be controlled by an electronic control unit. Alternatively, a plurality of electronic control units may be provided for controlling the valves  20  to  26 ,  32 ,  36 ,  38 ,  48 ,  50  and  54  to  58 . Furthermore, depending on the application requirements it is possible to dispense with some or all of the valves. The cooling systems  10  shown in  FIGS. 5 to 8  may moreover also be modified such that the process air line  28  branches off from the engine bleed air line  14 , not upstream, but downstream of the heat exchanger  12 . The compressor  40  may moreover be integrated into the cooling duct  52 .