Closed-loop heat transfer fluid system for an aircraft turbomachine and its pressure control method
The closed heat transfer fluid circuit with pressure regulation and controllable valves addresses pressure fluctuations, reducing mechanical stress and leak risks in aircraft turbomachines by stabilizing fluid pressure in the cryogenic fuel system.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- SAFRAN AIRCRAFT ENGINES SAS
- Filing Date
- 2024-11-08
- Publication Date
- 2026-05-15
AI Technical Summary
Significant pressure variations in the closed heat transfer fluid circuit of an aircraft turbomachine due to varying operating conditions lead to mechanical stress and increased risk of leaks, particularly in cryogenic fuel circuits.
A closed heat transfer fluid circuit with pressure regulation sections and controllable valves that adjust the fluid volume ratio between cold and hot branches to stabilize pressure, using compressible gases like nitrogen or helium, and control fluid flow through parallel lines based on pressure thresholds.
Reduces mechanical stress on equipment and minimizes the risk of leaks by stabilizing pressure variations, enhancing the service life and operational reliability of the cryogenic fuel system.
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Abstract
Description
Title of the invention: Closed-loop heat transfer fluid circuit for an aircraft turbomachine and its pressure control method. Technical field
[0001] The present invention relates to the field of pressure control in a closed circuit of heat transfer fluid for an aircraft turbomachine.
[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.
[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors affecting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental consequences, with the aim of improving the energy efficiency of aircraft.
[0004] This sustained research and development work focuses in particular on new generations of aircraft turbomachines powered by cryogenic fuels, such as hydrogen. Such an aircraft turbomachine conventionally comprises a cryogenic fuel circuit including, from upstream to downstream according to the direction of flow of the cryogenic fuel, a tank, a pressurization unit, a heating unit, a metering unit and a set of injectors.
[0005] As is known, the tank stores hydrogen in liquid form at a low temperature of approximately -253°C and a low pressure of less than 10 bar, so as to reduce its storage volume. The pressurization device, typically a pump, increases the pressure of the liquid hydrogen to maintain a pressure at the injectors higher than that in the combustion chamber. The heating device is typically in the form of a heat exchanger, in which the circulation of a heat transfer fluid, such as nitrogen or helium in a gaseous or supercritical state, heats the liquid hydrogen for the to make gaseous for combustion. The metering device, typically a valve known by its English name "fuel metering valve", allows the mass flow rate of gaseous hydrogen to be metered and distributed to the injectors for injection into the combustion chamber.
[0006] In a known manner, the heat transfer fluid supplying the heat exchanger of the cryogenic fuel circuit circulates in a closed loop within the aircraft turbomachine. After heating the cryogenic fuel, the heat transfer fluid is guided, via a cold branch, to a second heat exchanger where it is heated by a hot air stream, such as that circulating in the nozzle of the aircraft turbomachine. The heat transfer fluid is then reinjected into the heat exchanger of the cryogenic fuel circuit via a hot branch.
[0007] In practice, the average temperature of the heat transfer fluid in the closed circuit is subject to significant variations depending on the operating points within the flight envelope. This generates significant variations in absolute pressure within the closed circuit, typically exceeding 100 barA, which severely constrain the mechanical strength of the equipment and operational safety, particularly by increasing the risk of leaks in the cryogenic fuel circuit.
[0008] The invention thus aims to eliminate at least some of these drawbacks. PRESENTATION OF THE INVENTION
[0009] The invention relates to a closed heat transfer fluid circuit configured to be mounted in an aircraft turbomachine, the closed circuit comprising a first heat exchanger, in which the heat transfer fluid is configured to supply heat, and a second heat exchanger, in which the heat transfer fluid is configured to receive heat, the closed circuit comprising a cold branch configured to guide the heat transfer fluid from the first heat exchanger to the second heat exchanger, and a hot branch configured to guide the heat transfer fluid from the second heat exchanger to the first heat exchanger.
[0010] The invention is remarkable in that at least one of the cold branch and the hot branch of the closed circuit comprises: • at least one pressure regulation section comprising a first line and a second line extending in parallel between a branching point and a junction point, the first line comprising a first fluidic volume less than a second fluidic volume of the second line, • at least one controllable valve configured, when the heat transfer fluid pressure is below a first threshold, to guide the heat transfer fluid in the first line of the cold branch and / or in the second line of the hot branch, and when the pressure of the heat transfer fluid is greater than a second threshold greater than or equal to the first threshold, to guide the heat transfer fluid in the second line of the cold branch and / or in the first line of the hot branch.
[0011] The invention makes it possible to limit pressure variations in a closed circuit mounted in an aircraft, typically exceeding 100 bar, where the pressure varies according to the operating conditions of the aircraft turbomachine and external conditions. The pressure regulating section advantageously allows modification of the ratio between the fluid volume of the cold branch and the fluid volume of the hot branch, thereby modifying the average temperature in the closed circuit and thus the pressure. By limiting pressure variations in the closed circuit, the invention advantageously reduces the mechanical stresses on the equipment and thus increases its service life and operational reliability.
[0012] According to one aspect of the invention, the heat transfer fluid is in the form of a fluid in the gaseous or supercritical state, which is compressible. Preferably, the heat transfer fluid is in the form of nitrogen or helium.
[0013] According to one aspect of the invention, in the first heat exchanger, the heat transfer fluid is configured to heat a cryogenic fuel from a liquid state to a gaseous or supercritical state. Pressure regulation advantageously reduces mechanical stress on the cryogenic fuel circuit and the risk of leaks.
[0014] According to one aspect of the invention, in the second heat exchanger, the heat transfer fluid is configured to receive heat from an airflow of the aircraft turbomachine, preferably at the nozzle. This makes it possible to heat the heat transfer fluid exiting the first heat exchanger by utilizing the heat rejected by the aircraft turbomachine.
[0015] According to one aspect of the invention, the cold branch and the hot branch each comprise the pressure regulating section and the controllable valve. The pressure regulation is advantageously efficient with a small footprint.
[0016] Preferably, the controllable valve is configured, when the heat transfer fluid pressure is below a first threshold, to guide the heat transfer fluid into the first line of the cold branch and into the second line of the hot branch. This allows the pressure in the closed circuit to be raised simply and quickly.
[0017] Preferably, the controllable valve is configured, when the heat transfer fluid pressure is above a second threshold higher than the first threshold, to guide the heat transfer fluid in the second line of the cold branch and in the first hot branch line. This allows for a simple and quick reduction of pressure in the closed circuit.
[0018] Preferably, the controllable valve is configured, when the heat transfer fluid pressure is above the first threshold and below the second threshold, to guide the heat transfer fluid in the first line of the cold branch and in the first line of the hot branch. The first lines ensure the circulation of the heat transfer fluid when its pressure is within a nominal range.
[0019] According to another aspect of the invention, the cold branch or the hot branch comprises the pressure regulating section and the valve, the first threshold being equal to the second threshold. The other branch is free of a pressure regulating section for minimal space requirements.
[0020] According to one aspect of the invention, at least one of the cold and hot branches comprises a fluid volume via the second line that is at least 20% greater than its fluid volume via the first line, preferably at least 50% greater, and preferably at most three times greater. This makes it possible to sufficiently modify the proportion of the volume of one branch relative to the other to regulate the pressure in the closed circuit.
[0021] According to one aspect of the invention, the second line includes a storage tank. The first line is free of a storage tank. The second line thus has a larger fluid volume without additional piping length.
[0022] According to one aspect of the invention, the second line has a greater length and / or cross-section than the first line. This makes it possible to obtain, in a simple and practical way, a second fluidic volume greater than the first fluidic volume of the first line.
[0023] The invention also relates to a fuel system for an aircraft turbomachine comprising a closed circuit as described above and a fuel circuit configured to guide the fuel to the combustion chamber of the aircraft turbomachine, the first heat exchanger being mounted on the fuel circuit so as to heat the fuel by means of the heat transfer fluid. The invention advantageously allows the pressure in the closed heat transfer fluid circuit of a fuel circuit to be regulated in order to protect the fuel circuit equipment and prevent the risk of leaks.
[0024] Preferably, the fuel system is of the cryogenic type and comprises a tank configured to store the cryogenic fuel in a liquid state, the heat transfer fluid being configured to heat the cryogenic fuel from a liquid to a gaseous or supercritical state in the first heat exchanger. The invention is of particular interest in the case of a cryogenic fuel circuit where the mechanical stresses on the equipment are increased.
[0025] The invention also relates to an aircraft turbomachine comprising a fuel system as described above.
[0026] The invention also relates to a method for controlling the pressure of a heat transfer fluid in a closed circuit of an aircraft turbomachine as described above, in which: • when the heat transfer fluid pressure is below a first threshold, the controllable valve guides the heat transfer fluid into the first line of the cold branch and / or into the second line of the hot branch, and • when the pressure of the heat transfer fluid is greater than a second threshold greater than or equal to the first threshold, the controllable valve guides the heat transfer fluid into the second line of the cold branch and / or into the first line of the hot branch. PRESENTATION OF THE FIGURES
[0027] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.
[0028] Fig. 1 is a schematic representation of a closed heat transfer fluid circuit for heating cryogenic fuel in an aircraft turbomachine according to a first embodiment of the invention.
[0029] Fig. 2 is a schematic representation of the closed circuit of Fig. 1 when the pressure of the heat transfer fluid is greater than a second predetermined threshold.
[0030] Fig. 3 is a schematic representation of the closed circuit of Fig. 1 when the pressure of the heat transfer fluid is below a first predetermined threshold.
[0031] Fig. 4 is a schematic representation of a closed heat transfer fluid circuit for heating cryogenic fuel in an aircraft turbomachine according to a second embodiment of the invention.
[0032] Fig. 5 is a schematic representation of a closed heat transfer fluid circuit for heating cryogenic fuel in an aircraft turbomachine according to a third embodiment of the invention, when the heat transfer fluid pressure is below a predetermined threshold.
[0033] Fig. 6 is a schematic representation of the closed circuit of Fig. 5, when the pressure of the heat transfer fluid is greater than a predetermined threshold.
[0034] Fig. 7 is a schematic representation of a closed heat transfer fluid circuit for heating cryogenic fuel in an aircraft turbomachine according to a fourth embodiment of the invention, when the heat transfer fluid pressure is above a predetermined threshold.
[0035] Fig. 8 is a schematic representation of the closed circuit of Fig. 7, when the pressure of the heat transfer fluid is below a predetermined threshold.
[0036] It should be noted that the figures set out the invention in detail to implement the invention, said figures being of course able to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION
[0037] With reference to [Fig. 1], the invention relates to an aircraft turbomachine comprising a closed circuit 10 of heat transfer fluid F, in this example configured to heat a fuel circuit 1, in particular of the cryogenic type. The closed circuit 10 is so qualified in that no exchange of matter takes place between the heat transfer fluid F and the outside. The heat transfer fluid F is typically nitrogen or helium, in a gaseous or supercritical state, and therefore compressible.
[0038] As illustrated in [Fig. 1], the closed circuit 10 comprises: • a first heat exchanger 11, in which the heat transfer fluid F is configured to supply heat, typically to the cryogenic fuel H of the aircraft turbomachine, • a second heat exchanger 12, in which the heat transfer fluid F is configured to receive heat, typically from a hot air stream A from the aircraft turbomachine, • a cold branch 15 configured to guide the heat transfer fluid F from the first heat exchanger 11 to the second heat exchanger 12, • a hot branch 16 configured to guide the heat transfer fluid F from the second heat exchanger 12 to the first heat exchanger H, • typically, a pump 14 drives the heat transfer fluid F in the closed circuit 10, and • typically, a pressure sensor 13 adapted to measure the pressure P of the heat transfer fluid F in the closed circuit 10.
[0039] According to the invention and as illustrated in [Fig. 1], the cold branch 15, the hot branch 16 or each comprises a pressure regulating section 20, 30 comprising a first line 21, 31 and a second line 22, 32. The first line 21, 31 and the second line 22, 32 extend in parallel between a branching point 26, 36 and a junction point 27, 37 of the cold branch 15 and / or the hot branch 16. The first line 21, 31 has a first fluidic volume VI, VI* which is less than a second fluidic volume V2, V2* of the second line 22, 32.
[0040] According to the invention and with reference to [Fig.1], one or more controllable valves 24, 25, 34, 35 are configured, when the pressure P of the heat transfer fluid F is less than a first threshold Pmin (see [Fig.3]), to guide the heat transfer fluid F in the first line 21 of the cold branch 15 and / or in the second line 32 of the hot branch 16.
[0041] According to the invention and with reference to [Fig.1], the controllable valve(s) 24, 25, 34, 35 are configured, when the pressure P of the heat transfer fluid F is greater than a second threshold Pmax (see [Fig.2]), to guide the heat transfer fluid F into the second line 22 of the cold branch 15 and / or into the first line 31 of the hot branch 16.
[0042] The invention advantageously limits the variations in pressure P of the heat transfer fluid F in the closed circuit 10 that occur during aircraft flight. The pressure P of the heat transfer fluid F is directly related to the average temperature of the heat transfer fluid F, which varies according to the operating conditions of the aircraft turbomachine and external conditions.
[0043] To limit such variations, the pressure regulation section 20, 30 according to the invention advantageously allows modification of the ratio between the fluid volume Vf of the cold branch 15 and the fluid volume Vc of the hot branch 16, which results in a modification of the average temperature of the heat transfer fluid F. Indeed, the average temperature of the heat transfer fluid F satisfies the following equation: Tmoy = (Tf x Vf + Te x Vc ) / (Vf + Vc), with Tf and Te being the temperature of the heat transfer fluid F in the cold branch 15 and the hot branch 16, respectively. Thus, if the proportion of the fluid volume Vf of the cold branch 15 relative to the total volume Vf + Vc of the closed circuit 10 increases, which is achieved by directing the heat transfer fluid F in the second line 22 of the cold branch 15 and / or in the first line 31 of the hot branch 16, the average temperature Tmoy and, consequently, the pressure P of the heat transfer fluid F decrease.
[0044] By limiting pressure variations in the closed circuit 10, the invention advantageously reduces the mechanical stresses on the equipment, particularly the cryogenic fuel circuit 1, and thus increases its lifespan and operational reliability. The risk of leakage from the cryogenic fuel circuit 1 is advantageously reduced.
[0045] As illustrated in [Fig. 1], the first heat exchanger 11 is typically mounted on the fuel circuit 1 of the aircraft turbomachine so as to preheat the fuel H by heat exchange with the heat transfer fluid F before its injection into the combustion chamber. The first heat exchanger 11 is preferably mounted between a pressurization device 3, such as a pump, and a metering unit 4, typically a valve known by its English name "fuel metering valve", of the fuel circuit 1.
[0046] Preferably, the fuel H is cryogenic, typically hydrogen. The cryogenic fuel H is stored in one or more tanks 2 in a liquid state, at a low temperature of approximately -253°C and at a low pressure of less than 10 bar, so as to reduce its storage volume. The pressurization device 3 increases the pressure of the cryogenic fuel H to a value higher than that in the combustion chamber. The first heat exchanger 11 heats the cryogenic fuel H from a liquid to a gaseous or supercritical state. The metering device 4 controls the mass flow rate of the gaseous cryogenic fuel H distributed to the injectors 5 for injection into the combustion chamber.
[0047] With further reference to [Fig. 1], the second heat exchanger 12 is typically mounted in contact with a hot air stream A from the aircraft turbomachine, for example at the nozzle. This allows the heat transfer fluid F to be heated after passing through the first heat exchanger 11.
[0048] With reference to [Fig. 1], each pressure regulating section 20, 30 belongs to a single branch of the closed circuit 10, namely the cold branch 15 or the hot branch 16. The cold branch 15 fluidly connects the first heat exchanger 11 and the second heat exchanger 12 and forms a portion of the closed circuit 10 in which the heat transfer fluid F is cold. The hot branch 16 fluidly connects the first heat exchanger 11 and the second heat exchanger 12 and forms a portion of the closed circuit 10 in which the heat transfer fluid F is hot.
[0049] In the example of Figures 1 to 4, the cold branch 15 comprises a first pressure regulating section 20 and the hot branch 16 a second pressure regulating section 30. The first pressure regulating section 20 is defined between an upstream branch point 26 and a downstream junction point 27 of the cold branch 15 according to the direction of flow of the heat transfer fluid F. At the branch point 26, the cold branch 15 divides into the first line 21 and the second line 22, which rejoin at the junction point 27. Preferably, the cold branch 15 is in the form of a single line upstream of the branch point 26 and downstream of the junction point 27.
[0050] Similarly, the second pressure regulating section 30 is defined between an upstream branch point 36 and a downstream junction point 37 of the hot branch 16, according to the direction of flow of the heat transfer fluid F. At the branch point 36, the hot branch 16 divides into the first line 31 and the second line 32, which rejoin at the junction point 37. Preferably, the hot branch 16... presents itself in the form of a simple line upstream of the branching point 36 and downstream of the junction point 37.
[0051] In the example of Figures 5 and 6, only the cold branch 15 is provided with a pressure regulating section 20. In the example of Figures 7 and 8, only the hot branch 16 is provided with a pressure regulating section 30. This allows the pressure P to be regulated with minimal space requirements. Alternatively, several pressure regulating sections 20, 30 could extend in series on the cold branch 15 or the hot branch 16, but this would increase the overall size. A pressure regulating section 20, 30 is subsequently described independently of its position on the closed circuit 10.
[0052] As illustrated in Figures 1 to 8, the first line 21, 31 and the second line 22, 32 of a pressure regulating section 20, 30 differ from each other in that the second line 22, 32 has a second fluidic volume V2, V2* greater than a first fluidic volume VI, VI* of the first line 21, 31. In the example of [Fig. 4], the second line 22, 32 has a greater length and / or cross-section than the first line 21, 31. In the example of Figures 1 to 3, the second line 22, 32 also has a storage tank 23, 33, the first line 21, 31 having none. Preferably, the cold branch 15 comprises a fluidic volume Vf via the second line 22 greater than at least 20% than its fluidic volume Vf via the first line 21, preferably at least 50% and preferably at most three times greater.Preferably, the hot branch 16 comprises a fluidic volume Vc via the second line 32 which is at least 20% greater than its fluidic volume Vc via the first line 31, preferably at least 50% and preferably at most three times greater.
[0053] With reference to figures 1 to 8, the controllable valve(s) 24, 25, 34, 35 allow selection whether the heat transfer fluid F circulates in the first line 21, 31 or in the second line 22, 32 of a pressure regulation section 20, 30. A control device, such as an aircraft controller, ensures the controllable valves 24, 25, 34, 35 to allow fluid circulation in one or the other of the lines 21, 22, 31, 32.
[0054] In the examples of Figures 1 to 8, the controllable valves 24, 25, 34, 35 are in the form of check valves, typically of the non-return type, having an open position and a closed position. Preferably, the first line 21, 31 and the second line 22, 32 each comprise one or more check valves 24, 25, 34, 35. In this example, the first line 21, 31 comprises a single check valve 24, 34, and the second line 25, 35 comprises two check valves mounted respectively upstream and downstream of the second line 25, 35. The check valve(s) 24, 34 of the first line 21, 31 are controlled in opposition to the check valve(s) 25, 35 of the second line 22, 32. Alternatively, a three-way valve could be mounted at the branch point 26, 36 of a pressure regulating section 20, 30 to guide the heat transfer fluid F into either of the lines 21, 22, 31, 32.
[0055] With further reference to Figures 1 to 8, the controllable valves 24, 25, 34, 35 are controlled according to the pressure P of the heat transfer fluid F in the closed circuit 10 and a predetermined pressure threshold Pmin, Pmax, P1, P2. The pressure P of the heat transfer fluid F is determined from the operating conditions of the aircraft turbomachine and / or acquired by the pressure sensor 13. The pressure sensor 13 also allows, either additionally or alternatively, the measurement of a control pressure after the valves 24, 25, 34, 35 have been actuation.
[0056] According to a preferred aspect illustrated in figures 1 to 4, the cold branch 15 and the hot branch 16 each have at least one pressure regulating section 20, 30 and the controllable valves 24, 25, 34, 35 are controlled according to a first threshold Pmin of minimum pressure and a second threshold Pmax of maximum pressure.
[0057] As illustrated in [Fig. 1], when the pressure P of the heat transfer fluid F is between the thresholds Pmin, Pmax, the controllable valves 24, 34 allow circulation in the first lines 21, 31 only. In this example, the check valves 24, 34 of the first lines 21, 31 are open and the check valves 25, 35 of the second lines 22, 32 are closed.
[0058] As illustrated in [Fig. 2], if the pressure P increases and exceeds the maximum pressure threshold Pmax, typically at low engine speeds of the aircraft turbomachine, the controllable valves 24, 25 of the cold branch 15 divert the heat transfer fluid F into the second line 22. In this example, in the cold branch 15, the check valve 24 of the first line 21 is closed and the check valves 25 of the second line 22 are open. The circulation in the hot branch 16 remains unchanged, namely that the heat transfer fluid F circulates in the first line 31. The ratio of the volume of the cold branch 15 to the total volume of the closed circuit 10 increases, which reduces the average temperature and consequently the pressure P.
[0059] When the pressure P decreases below the maximum pressure threshold Pmax, the controllable valves 24, 25 of the cold branch 15 restore circulation in the first line 21 and close the second line 22, as illustrated in [Fig.1].
[0060] As illustrated in [Fig. 3], if the pressure P falls below the minimum pressure threshold Pmin, typically at high engine speed of the aircraft turbomachine, the controllable valves 34, 35 of the hot branch 16 divert the heat transfer fluid F into the second line 32. In this example, in the hot branch 16, the check valve 34 of the first line 31 is closed and the check valves 35 of the second line 32 are open. The circulation in the cold branch remains unchanged. namely that the heat transfer fluid F circulates in the first line 21. The ratio of the volume of the hot branch 16 to the total volume of the closed circuit 10 increases, which increases the average temperature and consequently the pressure P.
[0061] When the pressure P increases above the minimum pressure threshold Pmin, the controllable valves 34, 35 of the hot branch 16 restore circulation in the first line 31 and close the second line 32, as illustrated in [Fig.1].
[0062] According to another aspect illustrated in Figures 5 and 6, only the cold branch 15 includes at least one pressure regulating section 20. In this example, the controllable valves 24, 25 guide the heat transfer fluid F in the first line 21 when the pressure P is below a threshold PI and in the second line 22 when the pressure P is above the threshold PL
[0063] According to another aspect illustrated in figures 7 and 8, only the hot branch 16 has at least one pressure regulating section 30. In this example, the controllable valves 34, 35 guide the heat transfer fluid F in the first line 21 when the pressure P is greater than a threshold P2 and in the second line 22 when the pressure P is less than the threshold P2.
[0064] By modifying in a simple and practical way the volume proportion of the cold branch 15 and / or the hot branch 16, the invention advantageously allows the pressure P to be varied in a closed circuit 10 mounted in an aircraft turbomachine and subject to strong pressure variations.
Claims
Demands
1. A closed circuit (10) of heat transfer fluid (F) configured for mounting in an aircraft turbomachine, the closed circuit (10) comprising a first heat exchanger (11), in which the heat transfer fluid (F) is configured to supply heat, and a second heat exchanger (12), in which the heat transfer fluid (F) is configured to receive heat, the closed circuit (10) comprising a cold branch (15) configured to guide the heat transfer fluid (F) from the first heat exchanger (11) to the second heat exchanger (12), and a hot branch (16) configured to guide the heat transfer fluid (F) from the second heat exchanger (12) to the first heat exchanger (11), the closed circuit (10) being characterized in that at least one of the cold branch (15) and the hot branch (16) comprises: • at least one pressure regulating section (20, 30) including a first line (21,31) and a second line (22, 32) extending in parallel between a branch point (26, 36) and a junction point (27, 37), the first line (21, 31) comprising a first fluidic volume (VI, VI*) less than a second fluidic volume (V2, V2*) of the second line (22, 32), • at least one controllable valve (24, 25, 34, 35) configured, when the pressure (P) of the heat transfer fluid (F) is less than a first threshold (Pmin, PI, P2), to guide the heat transfer fluid (F) in the first line (21) of the cold branch (15) and / or in the second line (32) of the hot branch (16), and when the pressure (P) of the heat transfer fluid (F) is greater than a second threshold (Pmax, PI, P2) greater than or equal to the first threshold (Pmin, PI, P2), to guide the heat transfer fluid (F) in the second line (22) of the cold branch (15) and / or in the first line (31) of the hot branch (16).
2. Closed circuit (10) according to claim 1, in which the heat transfer fluid (F) is in the form of a fluid in the gaseous or supercritical state, preferably nitrogen or helium.
3. Closed circuit (10) according to any one of claims 1 and 2, wherein, in the first heat exchanger (11), the heat transfer fluid (F) is configured to heat a cryogenic fuel (H) from a liquid state to a gaseous or supercritical state.
4. Closed circuit (10) according to any one of claims 1 to 3, wherein the cold branch (15) and the hot branch (16) each comprise the pressure regulating section (20, 30) and the controllable valve (24, 25, 34, 35).
5. Closed circuit (10) according to claim 4, wherein the controllable valve (24, 25, 34, 35) is configured, when the pressure (P) of the heat transfer fluid (F) is greater than the first threshold (Pmin) and less than the second threshold (Pmax), to guide the heat transfer fluid (F) in the first line (21) of the cold branch (15) and in the first line (31) of the hot branch (16).
6. Closed circuit (10) according to any one of claims 1 to 3, wherein the cold branch (15) or the hot branch (16) comprises the pressure regulating section (20, 30) and the controllable valve (24, 25, 34, 35), the first threshold (PI, P2) being equal to the second threshold (PI, P2).
7. Closed circuit (10) according to any one of claims 1 to 6, wherein at least one of the cold branch (15) and the hot branch (16) comprises a fluidic volume (Vc, Vf) via the second line (22, 32) greater by at least 20% than its fluidic volume (Vc, Vf) via the first line (21, 31).
8. Closed circuit (10) according to any one of claims 1 to 7, wherein the second line (22, 32) comprises a storage tank (23, 33).
9. Closed circuit (10) according to any one of claims 1 to 8, wherein the second line (22, 32) has a length and / or cross-section greater than that of the first line (21, 31).
10. A method for controlling the pressure (P) of a heat transfer fluid (F) in a closed circuit (10) of an aircraft turbomachine according to any one of claims 1 to 9, wherein: • when the pressure (P) of the heat transfer fluid (F) is below a first threshold (Pmin, PI, P2), the controllable valve (24, 25, 34, 35) guides the heat transfer fluid (F) into the first line (21) of the cold branch (15) and / or in the second line (32) of the hot branch (16), and when the pressure (P) of the heat transfer fluid (F) is greater than a second threshold (Pmax, PI, P2) greater than or equal to the first threshold (Pmin, PI, P2), the controllable valve (24, 25, 34, 35) guides the heat transfer fluid (F) into the second line (22) of the cold branch (15) and / or into the first line (31) of the hot branch (16).