System and method for cooling and power generation on high-speed aircraft

Abstract

The present disclosure relates to systems and methods for cooling and power generation on high-speed aircraft. Methods and apparatus for cooling surfaces on an aircraft and / or power generation include advancing the aircraft at a speed of at least Mach 3.5, thereby aerodynamically heating the surface. A supercritical working fluid is circulated through a fluid circuit, the circulation comprising: compressing the supercritical working fluid through a compressor; heating the supercritical working fluid through a heat sink thermally coupled to the surface; expanding the supercritical working fluid in a heat engine to produce a work output; cooling the supercritical working fluid; and recirculating the supercritical working fluid to the compressor. The work output of the heat engine is operatively coupled to the compressor and optionally coupled to a generator to generate electricity. The supercritical working fluid absorbs heat from the surface, thereby eliminating hot spots and allowing the use of lighter and / or cheaper materials.

Description

Technical Field

[0001] The present disclosure generally relates to high-speed aircraft, and more particularly, to systems and methods for thermal management and power generation on high-speed aircraft. Background Art

[0002] An aircraft traveling at high speed in the atmosphere is subject to aerodynamic heating of its external surfaces and wetted duct surfaces. When traveling at speeds greater than Mach 3, and more specifically at hypersonic speeds greater than Mach 5, the temperature of these surfaces can locally exceed 1000 degrees Celsius, and thus high-density materials such as superalloys or expensive non-metallic materials such as ceramic matrix composites must be used. Additionally, turbofan and turbojet engines cannot be used at speeds greater than approximately Mach 3, thereby limiting their ability to operate a generator to power the aircraft systems. Summary of the Invention

[0003] In accordance with one aspect of the present disclosure, a method of cooling a surface on an aircraft includes advancing the aircraft at a flight speed of at least Mach 3, wherein the surface of the aircraft is aerodynamically heated. Circulating a supercritical working fluid through a fluid circuit, the circulation sequentially including: compressing the supercritical working fluid by a compressor; heating the supercritical working fluid by a heat absorbing device of the fluid circuit, wherein the heat absorbing device of the fluid circuit is thermally coupled to the surface of the aircraft; expanding the supercritical working fluid in a heat engine, thereby generating a work output from the heat engine; cooling the supercritical working fluid; and recirculating the supercritical working fluid to the compressor. Operatively coupling the work output of the heat engine to the compressor.

[0004] In accordance with another aspect of the present disclosure, a system for cooling a surface of an aircraft traveling at a flight speed of at least Mach 3 is provided. The system includes a fluid circuit that contains a supercritical working fluid. The fluid circuit sequentially includes: a compressor for compressing the supercritical working fluid; a heat absorbing device that is arranged in a thermally coupled relationship with the surface of the aircraft for heating the supercritical working fluid; a heat engine for expanding the supercritical working fluid and generating a work output, wherein the work output is operatively coupled to the compressor; and a heat exchanger for exchanging heat from a low-pressure branch of the fluid circuit to a high-pressure branch of the fluid circuit, the low-pressure branch being downstream of the heat engine and the high-pressure branch being upstream of both the heat engine and the heat absorbing device of the fluid circuit.

[0005] In other aspects of the present disclosure, a system for cooling a surface of an aircraft and generating electricity is provided. The system includes a fluid circuit that contains a supercritical working fluid. The fluid circuit sequentially includes: a compressor for compressing the supercritical working fluid; a heat absorber disposed in a thermally coupled relationship with the surface of the aircraft for heating the supercritical working fluid; a heat engine for expanding the supercritical working fluid and generating a work output, wherein the work output is operatively coupled to the compressor; a heat exchanger for exchanging heat from a lower pressure branch of the fluid circuit to a higher pressure branch, the lower pressure branch being downstream of the heat engine and the higher pressure branch being upstream of both the heat engine and the heat absorber in the fluid circuit. A generator is operatively coupled to the heat engine and is configured to receive at least a portion of the work output and generate auxiliary power. A controller is operatively coupled to the compressor, wherein the controller is programmed to perform a method that includes operating the compressor when the flight speed of the aircraft is greater than Mach 3.

[0006] The features, functions, and advantages discussed can be implemented independently in various examples or combined in other examples. Other details of these examples can be found with reference to the following description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Novel features that are considered characteristic of exemplary embodiments are set forth in the appended claims. However, the exemplary embodiments as well as preferred modes of use, other objectives, and advantages will be best understood by reference to the following detailed description of exemplary examples of the present disclosure when read in conjunction with the accompanying drawings, wherein:

[0008] Figure 1 is a perspective view of a high-speed aircraft having an integrated cooling and power generation system according to the present disclosure.

[0009] Figure 2 is a schematic illustration of the integrated cooling and power generation system.

[0010] Figure 3 is a graph illustrating an exemplary supercritical fluid for the integrated cooling and power generation system.

[0011] Figure 4 is a block diagram of an example of an integrated cooling and power generation system having a mechanical connection between a turbine and a compressor of the system.

[0012] Figure 5 is a block diagram of another example of an integrated cooling and power generation system having an electrical connection between a turbine and a compressor of the system.

[0013] Figure 6 illustrates cooling Figure 1Block diagram of a method for the outer surface of a high-speed aircraft, where power generation is optional. Detailed implementation

[0014] The accompanying drawings and the following description illustrate specific examples of the claimed subject matter. Accordingly, it should be understood that those skilled in the art will be able to design various arrangements that, although not explicitly described or shown herein, implement the principles of the examples and are included within the scope of the examples. In addition, any examples described herein are intended to assist in understanding the principles of the disclosed subject matter's construction, operation, or other features, and should be construed as not limited to such specifically recited examples and conditions. Therefore, the inventive concept is not limited to the specific examples described below, but is defined by the claims and their equivalents.

[0015] The examples described herein cool the surface of a high-speed aircraft by circulating a supercritical working fluid through a fluid circuit having a compressor and a heat engine. When the aircraft travels at greater than Mach 3, some portions of the aircraft's surface may reach 1000 degrees Celsius or higher. The supercritical working fluid absorbs heat from the aircraft's surface, thereby eliminating hot spots and allowing the use of lighter and / or less expensive materials. The heat generated at high speeds and absorbed by the working fluid keeps the working fluid in a supercritical state, allowing the compressor, heat engine, and other components of the cooling system to be smaller and lighter. Further, the heat absorbed by the working fluid can be used to generate electricity for the aircraft. The supercritical state of the working fluid improves the thermal efficiency of the system, and the combination of the improved thermal efficiency of the system and the use of lightweight turbomachinery results in a compact, lightweight, and efficient power source compared to conventional batteries or fuel cells.

[0016] Figure 1 An example of a high-speed aircraft 102 is illustrated. As needed, the aircraft 102 can be operated manned or unmanned. The aircraft 102 is merely one configuration of an aircraft capable of traveling at at least Mach 3, and other configurations not shown can be implemented as needed. For example, as needed, the aircraft 102 can have different shapes, sizes, aspect ratios, etc. Therefore, for the purpose of discussion, the aircraft 102 is shown only in a specific configuration.

[0017] In this example, the aircraft 102 has a surface 104 that is exposed to aerodynamic heating. In some examples, the surface 104 is disposed on the leading face of the aircraft 102, such as on the wing 106, tail 108, nose cowl 110, or intake 112. During operation of the aircraft 102 at greater than Mach 3 or during hypersonic flight (e.g., the aircraft 102 moves at hypersonic speeds above Mach 5), the surface 104 is aerodynamically heated. For example, the temperature of the surface 104 can exceed 1000 degrees Celsius.

[0018] The aircraft 102 includes a system 100 for cooling a surface 104, thereby allowing the surface 104 to be formed of low-cost and / or lighter materials. As Figure 2 Best shown in, the system 100 includes a fluid circuit 120 through which a working fluid 122 circulates. In the illustrated example, the fluid circuit 120 is formed as a closed loop. When the aircraft 102 operates at a speed greater than Mach 3, heat from the surface 104 is transferred to the working fluid 122 in the fluid circuit 120, thereby maintaining the working fluid 122 at a temperature and pressure above its critical point. Figure 3 The critical point of a substance is illustrated by a curve, where temperatures and pressures above the critical point will result in a supercritical state. In some examples, the working fluid is supercritical carbon dioxide.

[0019] The system 100 includes components disposed in the fluid circuit 120 that are configured to perform a series of thermodynamic processes that involve transferring heat and work into and out of the system 100 while changing the temperature and pressure of the working fluid 122 within the system. As Figure 2 Schematically illustrated in, the system 100 includes a compressor 130 for compressing the supercritical working fluid 122 to an increased pressure. The system 100 also includes a heat absorber 140 that absorbs heat from a source external to the fluid circuit 120 to heat the supercritical working fluid 122. In the illustrated example, the external source is the surface 104 of the aircraft 102, and the heat absorber 140 is a portion of the fluid circuit 120 that is arranged in a thermally coupled relationship with the surface 104.

[0020] The system 100 also includes a heat engine 150 that extracts a work output 152 from the supercritical working fluid by expanding the supercritical working fluid 122 to a reduced pressure. Although Figure 2 Schematically illustrated as a turbine, other types of heat engines capable of extracting a work output from a heated and pressurized working fluid may be used. In the illustrated example, the work output 152 takes the form of a rotating output shaft of the turbine, and the rotating output shaft is mechanically coupled to the compressor 130 by a shaft 154, thereby operating the compressor 130. However, as discussed in more detail below, in addition to being electrically coupled to a power generation device, the work output 152 may also be electrically coupled to the compressor 130. Additionally, it should be understood that the compressor 130 and the heat engine 150 generally divide the fluid circuit 120 into a low-pressure branch 124 and a high-pressure branch 126, with the low-pressure branch 124 extending downstream of the heat engine 150 to the inlet of the compressor 130 and the high-pressure branch 126 extending upstream of the heat engine 150 to the outlet of the compressor 130.

[0021] A heat exchanger 160 is provided to improve the thermal efficiency of the system 100. As Figure 2Illustrated schematically, heat exchanger 160 transfers heat from the low-pressure branch 124 of fluid circuit 120 to the high-pressure branch 126 of the fluid circuit. Thus, heat exchanger 160 is alternatively referred to as a recuperator. By transferring heat to working fluid 122 before it is further heated by endothermic device 140, the temperature of working fluid 122 entering heat engine 150 is increased, thereby increasing the amount of work output 152 that can be extracted from the working fluid.

[0022] A controller 200 may be provided to control the operation of system 100. In Figure 2 , controller 200 is operatively coupled to compressor 130 and is programmed to perform a method that includes initiating operation of compressor 130 when one or more operating conditions of aircraft 102 favor maintaining working fluid 122 in a supercritical state. In some examples, the operating condition is the temperature of surface 104, in which case controller 200 receives feedback from sensor 202 configured to detect the temperature of surface 104 and is programmed to initiate compressor 130 when the surface 104 of aircraft 102 exceeds a threshold temperature. Exemplary threshold temperatures include, but are not limited to, 500 degrees Celsius, 600 degrees Celsius, 700 degrees Celsius, 800 degrees Celsius, 900 degrees Celsius, and 1000 degrees Celsius. In other examples, the operating condition is the flight speed of aircraft 102 indicative of the temperature of surface 104. In these examples, controller 200 receives an indication of the flight speed, such as from an input command or sensor 202 (when configured to determine flight speed), and is programmed to initiate compressor 130 when the aircraft reaches a threshold flight speed. Exemplary threshold flight speeds include, but are not limited to, Mach 3, Mach 3.5, Mach 4, and hypersonic. Additionally, controller 200 may be operatively coupled to heat engine 150.

[0023] Although the specific hardware implementation of controller 200 is influenced by design choices, one specific example includes one or more processors coupled to a current driver. The one or more processors may include any electronic and / or optical circuitry capable of performing the functions described herein. For example, the one or more processors may perform any of the functions described herein for controller 200. The one or more processors may include one or more central processing units (CPUs), microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), programmable logic devices (PLDs), control circuitry, etc. Some examples of processors include CORE TM processors, advanced reduced instruction set computing (RISC) machines processors, etc.

[0024] System 100 is configured to maintain working fluid 122 in a supercritical state throughout a thermodynamic cycle, thereby enabling the use of lighter and more compact turbomachinery. For example, when working fluid 122 is, for example, carbon dioxide, the critical temperature is approximately 31 degrees Celsius and the critical pressure is approximately 74 bar. Aerodynamic heating of surface 104 increases with the speed of aircraft 102. For example, at a speed of 3.5 Mach, local portions of surface 104 reach 400 degrees Celsius or higher, which would be sufficient to maintain working fluid 122 in a supercritical state. At hypersonic speeds above 5 Mach, local portions of surface 104 may reach 1000 degrees Celsius. The thermodynamic efficiency of system 100 increases with the temperature of surface 104. Additionally, the size of compressor 130 is sized to maintain the pressure of working fluid 122 above the critical pressure throughout the thermodynamic cycle. Since working fluid 122 is in a supercritical state, compressor 130 and heat engine 150 can have reduced size and weight, making system 100 viable for use on aircraft 102. Additionally, the illustrated system 100 is a closed-loop system that is provided independently of the propulsion system of aircraft 102.

[0025] In some examples, system 100 is also configured to generate electricity 172. As Figure 2 schematically illustrated, system 100 may include a generator 170 operatively coupled to heat engine 150. Generator 170 receives at least a portion of the work output 152 from heat engine 150 and generates electricity 172. In this example, an auxiliary load 180 is operatively coupled to generator 170 and is configured to operate using electricity 172. In other examples, electricity 172 may be the primary power source for operating an engine generator. Controller 200 may also be operatively coupled to generator 170 and auxiliary load 180, thereby controlling the operation or other aspects of those components. In examples that include generator 170, system 100 may alternatively be referred to as an integrated cooling and power generation system 100. Due to the thermal efficiency, compact size, and reduced weight provided by using supercritical working fluid 122, integrated cooling and power generation system 100 achieves a gravitational and volumetric power density that is an order of magnitude greater than that of batteries or other conventional power sources.

[0026] System 100 may also include a pre-cooler 190 for removing excess heat from working fluid 122. As Figure 2Exemplarily illustrated, the pre-cooler 190 includes a pre-cooler heat exchanger 191 disposed in the low-pressure branch 124 of the fluid circuit 120, between the heat exchanger 160 and the compressor 130. By removing heat from the working fluid 122, the pre-cooler 190 ensures that the temperature of the working fluid 122 does not exceed the rated operating temperature range of the compressor 130. The excess heat is dissipated into the surrounding atmosphere or transferred to an auxiliary fluid in another system on the aircraft 102. In the illustrated example, the pre-cooler 190 further includes a radiator circuit 193 passing through the pre-cooler heat exchanger 191. The radiator circuit 193 transports the excess waste heat to a storage structure such as a container containing a radiator fluid 192 (e.g., fuel, water, or other fluid carried on the aircraft 102) or a thermal energy storage device 194. Subsequently, the excess heat can be used to generate additional electricity, provide heat to other systems on the aircraft 102, or simply be dissipated into the surrounding environment.

[0027] Figure 4 FIG. 220 is a block diagram illustrating a thermodynamic cycle during operation of the system 100 when the compressor 130 is mechanically driven. In block 222, the working fluid 122 is heated by the surface 104 via the heat absorption device 140. In block 224, the working fluid 122 expands in the heat engine 150 to obtain a work output 152, which in the illustrated example is a rotating shaft. Next, in block 226, heat from the expanded working fluid 122 is transferred from the low-pressure branch 124 to the high-pressure branch 126 of the fluid circuit 120 through the heat exchanger 160. In this way, the heat exchanger 160 collects heat from the expanded working fluid 122. Block 228 illustrates an optional step of using the pre-cooler 190 to transfer excess heat from the working fluid 122 to the radiator circuit 193. In this way, the excess heat is dissipated into the aircraft radiator circuit 193. At block 230, the compressor 130 compresses the working fluid 122, thereby driving the working fluid 122 through the system (e.g., the fluid circuit 120). In this example, the compressor 130 is mechanically coupled to the heat engine 150 by a shaft 154 such that the work output 152 directly and mechanically operates (e.g., drives) the compressor 130. Block 232 schematically illustrates heating the working fluid 122 via the heat exchanger 160. In this way, the temperature of the working fluid 122 in the compressed state is preheated. Then, in block 222, the working fluid 122 reaches the heat absorption device 140, where the cycle is repeated. Block 234 illustrates an optional step of using at least a portion of the work output 152 to drive the generator 170, and block 236 illustrates an optional step of powering an auxiliary load 180 from the generator. Thus, in this example, the work output 152 from the heat engine 150 both mechanically operates the compressor 130 and generates electricity in the generator 170.

[0028] Figure 5 is a block diagram 240 illustrating a thermodynamic cycle in a system 100 having an electrically driven compressor 130. Except for how the work output 152 is used, the stages of this cycle are the same as those shown in Figure 4 , so the description of this example will focus only on those differences. Notably, the system 100 omits the shaft 154 extending between the heat engine 150 and the compressor 130. Using the work output 152 to drive the generator 170, illustrated in block 234, is no longer optional but required. The compressor 130 is electrically coupled to the generator 170, thereby driving the compressor 130. Powering the auxiliary load 180, shown in block 236, remains optional and may be omitted, in which case the generator 170 is directly coupled to the compressor 130. Thus, in this example, the work output 152 from the heat engine 150 is fully converted into electricity, which can be used to operate the compressor 130 and optionally the auxiliary load 180.

[0029] Figure 6 is a block diagram illustrating a method 300 for cooling the outer surface 104 of a high-speed aircraft 102, where power generation is optional. Method 300 begins at block 302, advancing the aircraft 102 at a flight speed of at least Mach 3, where the surface 104 of the aircraft 102 acquires heat. At block 304, a supercritical working fluid 122 is circulated through a fluid circuit 120. The circulation of the working fluid 122 sequentially includes: compressing the supercritical working fluid 122 by a compressor 130 as shown in block 306; heating the supercritical working fluid 122 by a heat absorption device 140 of the fluid circuit 120 in block 308, where the heat absorption device 140 of the fluid circuit 120 is thermally coupled to the surface 104 of the aircraft 102; and expanding the supercritical working fluid 122 in a heat engine 150 at block 310, thereby generating a work output 152 from the heat engine 150. The circulation of the working fluid 122 through the fluid circuit 120 also includes: cooling the supercritical working fluid 122 at block 312; and recycling the supercritical working fluid 122 to the compressor 130 at block 314. Method 300 continues at block 316, operatively coupling the work output 152 of the heat engine 150 to the compressor 130. In this way, method 300 absorbs heat from the surface 104 of the aircraft 102, thereby allowing the surface 104 to be formed of less costly and / or lighter materials and using the absorbed heat to operate the compressor 130.

[0030] Method 300 may include additional optional steps for generating electricity. For example, as Figure 6As schematically shown in, method 300 may include generating electricity in block 318 by operably coupling the work output 152 of heat engine 150 to generator 170. When compressor 130 is an electric compressor, the electricity from generator 170 may be used to operate compressor 130. Additionally or alternatively, the electricity from generator 170 may be used to power auxiliary load 180, as shown in block 320.

[0031] Further, method 300 may optionally include additional steps to reduce the temperature of working fluid 122 to a recommended range for compressor 130. Specifically, method 300 may include using precooler 190 to dissipate heat from supercritical working fluid 122 before recirculating the supercritical working fluid 122 to compressor 130, as shown in block 322.

[0032] Additionally, the present disclosure includes examples according to the following clauses:

[0033] Clause 1. A method of cooling a surface on an aircraft, the method comprising: advancing the aircraft at a flight speed of at least Mach 3, wherein the surface of the aircraft is aerodynamically heated; circulating a supercritical working fluid through a fluid circuit, the circulation sequentially including: compressing the supercritical working fluid by a compressor; heating the supercritical working fluid by a heat absorbing device of the fluid circuit, wherein the heat absorbing device of the fluid circuit is thermally coupled to the surface of the aircraft; expanding the supercritical working fluid in a heat engine, thereby generating a work output from the heat engine; cooling the supercritical working fluid; and recirculating the supercritical working fluid to the compressor; and operably coupling the work output of the heat engine to the compressor.

[0034] Clause 2. The method according to clause 1, the method further comprising: generating electricity by operably coupling the work output of the heat engine to a generator.

[0035] Clause 3. The method according to clause 2, wherein the compressor comprises an electric compressor operably coupled to the generator.

[0036] Clause 4. The method according to clause 2, the method further comprising: using the generator to power an auxiliary load.

[0037] Clause 5. The method according to any one of clauses 1 to 4, wherein cooling the supercritical working fluid comprises: exchanging heat from a low pressure branch of the fluid circuit to a high pressure branch of the fluid circuit, the low pressure branch being downstream of the heat engine and the high pressure branch being upstream of both the heat engine and the heat absorbing device of the fluid circuit.

[0038] Clause 6. The method according to Clause 5, wherein a heat exchanger is provided to exchange heat from the low-pressure branch of the fluid circuit to the high-pressure branch of the fluid circuit.

[0039] Clause 7. The method according to any one of Clauses 1 to 6, the method further comprising: dissipating heat from the supercritical working fluid via a pre-cooler before recirculating the supercritical working fluid to the compressor.

[0040] Clause 8. The method according to any one of Clauses 1 to 7, wherein the supercritical working fluid comprises supercritical carbon dioxide.

[0041] Clause 9. A system for cooling the surface of an aircraft traveling at a flight speed of at least Mach 3, the system comprising: a fluid circuit containing a supercritical working fluid, the fluid circuit sequentially comprising: a compressor for compressing the supercritical working fluid; a heat absorption device arranged in thermal coupling relation with the surface of the aircraft for heating the supercritical working fluid; a heat engine for expanding the supercritical working fluid and generating a work output, wherein the work output is operatively coupled to the compressor; and a heat exchanger for exchanging heat from the low-pressure branch of the fluid circuit to the high-pressure branch of the fluid circuit, the low-pressure branch being downstream of the heat engine and the high-pressure branch being upstream of both the heat engine and the heat absorption device of the fluid circuit.

[0042] Clause 10. The system according to Clause 9, the system further comprising a generator operatively coupled to the heat engine and configured to receive at least a portion of the work output and generate electricity.

[0043] Clause 11. The method according to Clause 10, wherein the compressor comprises an electric compressor operatively coupled to the generator.

[0044] Clause 12. The system according to any one of Clauses 9 to 11, the system further comprising a pre-cooler operatively coupled to the low-pressure branch of the fluid circuit and located between the heat exchanger and the compressor.

[0045] Clause 13. The system according to any one of Clauses 9 to 12, the system further comprising a controller operatively coupled to the compressor, wherein the controller is programmed to execute a method that includes starting the operation of the compressor when the operating conditions of the aircraft exceed an operating threshold.

[0046] Clause 14. The system according to Clause 13, wherein the operating conditions of the aircraft (102) include the temperature of the surface.

[0047] Clause 15. The system according to Clause 13, wherein the operating conditions of the aircraft include the flight speed of the aircraft.

[0048] Clause 16. A system for cooling a surface of an aircraft and generating electricity, the system comprising: a fluid circuit containing a supercritical working fluid, the fluid circuit sequentially including: a compressor for compressing the supercritical working fluid; a heat absorber arranged in thermal coupling relationship with the surface of the aircraft for heating the supercritical working fluid; a heat engine for expanding the supercritical working fluid and generating a work output, wherein the work output is operatively coupled to the compressor; a heat exchanger for exchanging heat from a low-pressure branch of the fluid circuit to a high-pressure branch of the fluid circuit, the low-pressure branch being downstream of the heat engine and the high-pressure branch being upstream of both the heat engine and the heat absorber of the fluid circuit; a generator operatively coupled to the heat engine and configured to receive at least a portion of the work output and generate auxiliary power; and a controller operatively coupled to the compressor, wherein the controller is programmed to perform a method that includes operating the compressor when the flight speed of the aircraft is greater than Mach 3.

[0049] Clause 17. The method according to Clause 16, wherein the compressor includes an electric compressor operatively coupled to the generator.

[0050] Clause 18. The system according to any one of Clauses 16 to 17, the system further including an auxiliary load operatively coupled to the generator.

[0051] Clause 19. The system according to any one of Clauses 16 to 18, the system further including a precooler operatively coupled to the low-pressure branch of the fluid circuit and located between the heat exchanger and the compressor.

[0052] Clause 20. The system according to Clause 19, wherein the precooler includes a radiator fluid or a thermal energy storage device.

[0053] As used herein, the term "sequence" generally relates to elements in order (e.g., unit operations). Such a sequence can refer to a process sequence such as (e.g.) the sequence in which fluid flows from one element to another. In an example, a compressor, a thermal storage unit, and a turbine in sequence include a compressor upstream of a heat exchange unit and a heat exchange unit upstream of the turbine. In such a case, fluid can flow from the compressor to the heat exchange unit and from the heat exchange unit to the turbine. Fluid flowing sequentially through unit operations can flow through the unit operations in sequence. A series of elements can include one or more intermediate elements. For example, a system including a compressor, a thermal storage unit, and a turbine in sequence can include an auxiliary tank between the compressor and the thermal storage unit. A series of elements can be cyclic.

[0054] Any of the various elements shown in the figures or described herein can be implemented as hardware, software, firmware, or some combination thereof. For example, an element can be implemented as dedicated hardware. Dedicated hardware elements can be referred to as "processors", "controllers", or some similar terms. When provided by a processor, these functions can be provided by a single dedicated processor, a single shared processor, or multiple individual processors, some of which can be shared. Additionally, the explicit use of the term "processor" or "controller" should not be construed as exclusively referring to hardware capable of executing software, and can implicitly include, without limitation, digital signal processor (DSP) hardware, network processors, application specific integrated circuits (ASICs) or other circuitry, field programmable gate arrays (FPGAs), read only memory (ROM) for storing software, random access memory (RAM), non-volatile memory, logic devices, or some other physical hardware component or module.

[0055] Alternatively, an element can be implemented as instructions executable by a processor or computer to perform the functions of the element. Some examples of instructions are software, program code, and firmware. The instructions are operable, when executed by the processor, to direct the processor to perform the functions of the element. The instructions can be stored on a processor-readable storage device. Some examples of storage devices are digital or solid state memories, magnetic storage media such as disks and tapes, hard drives, or optically readable digital data storage media.

[0056] Although specific examples are described herein, the scope is not limited to those specific examples. Rather, the scope is defined by the appended claims and any equivalents thereof.

Claims

1. A method (300) of cooling a surface (104) on an aircraft (102), the method comprising: Propelling the aircraft (102) at a flight speed of at least Mach 3, wherein the surface (104) of the aircraft (102) is aerodynamically heated; A supercritical working fluid (122) is circulated through a fluid circuit (120) of a closed-loop system independent of a propulsion system of the aircraft (102), the circulation comprising, in sequence: compressing the supercritical working fluid (122) by a compressor (130); heating the supercritical working fluid (122) via a heat sink (140) of the fluid circuit (120), wherein the heat sink (140) of the fluid circuit (120) is thermally coupled to the surface (104) of the aircraft (102); causing the supercritical working fluid (122) to expand in a heat engine (150), thereby generating a work output (152) from the heat engine (150); Cooling the supercritical working fluid (122), wherein cooling the supercritical working fluid (122) comprises: exchanging heat from a low-pressure branch (124) of the fluid circuit (120) to a high-pressure branch (126) of the fluid circuit (120), wherein the low-pressure branch (124) is located downstream of the heat engine (150), and the high-pressure branch (126) is located upstream of both the heat engine (150) and the heat sink (140) of the fluid circuit (120); and recirculating the supercritical working fluid (122) to the compressor (130); and The work output (152) of the heat engine (150) is operatively coupled to the compressor (130).

2. The method (300) according to claim 1, further comprising: Electricity is generated by operatively coupling the work output (152) of the heat engine (150) to a generator (170).

3. The method (300) according to claim 2, wherein: The compressor (130) comprises an electric compressor operatively coupled to the generator (170).

4. The method (300) according to claim 2, further comprising: The generator (170) is used to power an auxiliary load (180).

5. The method (300) of claim 1, wherein: A heat exchanger (160) is provided to exchange heat from the low-pressure branch (124) of the fluid circuit (120) to the high-pressure branch (126) of the fluid circuit (120).

6. The method (300) according to any one of claims 1 to 5, further comprising: Heat is dissipated from the supercritical working fluid (122) via a precooler (190) before the supercritical working fluid (122) is recycled to the compressor (130).

7. The method (300) according to any one of claims 1 to 5, wherein: The supercritical working fluid (122) includes supercritical carbon dioxide.

8. A system (100) for cooling a surface (104) of an aircraft (102) travelling at a flight speed of at least Mach 3, wherein: The system (100) is a closed-loop system that is independent of the propulsion system of the aircraft (102), and the system (100) comprises: A fluid circuit (120) containing a supercritical working fluid (122), the fluid circuit (120) comprising, in order: A compressor (130) for compressing the supercritical working fluid (122); a heat sink (140) arranged to be thermally coupled to the surface (104) of the aircraft (102) for heating the supercritical working fluid (122); a heat engine (150) for expanding the supercritical working fluid (122) and producing a work output (152), wherein the work output (152) is operatively coupled to the compressor (130); and A heat exchanger (160) is used to exchange heat from a low-pressure branch (124) of the fluid circuit (120) to a high-pressure branch (126) of the fluid circuit (120), wherein the low-pressure branch (124) is located downstream of the heat engine (150), and the high-pressure branch (126) is located upstream of both the heat engine (150) and the heat absorption device (140) of the fluid circuit (120).

9. The system (100) of claim 8, further comprising a generator (170) operatively coupled to the heat engine (150) and configured to receive at least a portion of the work output (152) and generate electricity (172).

10. The system (100) according to claim 9, wherein: The compressor (130) comprises an electric compressor operatively coupled to the generator (170).

11. The system (100) according to any one of claims 8 to 10, further comprising a precooler (190) operatively coupled to the low pressure branch (124) of the fluid circuit (120) between the heat exchanger (160) and the compressor (130).

12. The system (100) according to any one of claims 8 to 10, further comprising a controller (200) operatively coupled to the compressor (130), wherein: The controller (200) is programmed to perform a method including initiating operation of the compressor (130) when an operating condition of the aircraft exceeds an operating threshold.

13. The system (100) according to claim 12, wherein: The operating conditions of the aircraft (102) include a temperature of the surface (104).

14. The system (100) according to claim 12, wherein: The operating condition of the aircraft (102) includes a flight speed of the aircraft (102).

Images