Refrigerant circuit for an aircraft propulsion assembly and method for using same

Abstract

The invention relates to a refrigerant circuit (29) for an aircraft propulsion assembly, comprising: - a heat exchanger (1) comprising a circulation channel (3) for a refrigerant (H); - a supply line (15) configured to supply the circulation channel (3) with refrigerant (H); - a drainage line (10) comprising a tank (12) configured to store the drainage air at a drainage pressure (Pvid) and an intake valve (13) comprising, when the drainage pressure (Pvid) is greater than an internal pressure (Pint) of the refrigerant (H) in the heat exchanger (1), an open position (ON) allowing the drainage air stored in the tank (12) to circulate from upstream to downstream in the circulation channel (3) so as to drain the heat exchanger (1) of the refrigerant (H) during in-flight stopping of the aircraft propulsion assembly.

Description

Refrigerant circuit for an aircraft propulsion system and its method of use

[0001] The present invention relates to the field of refrigerant fluid circuits for an aircraft propulsion system.

[0002] As is known, an aircraft turbomachine comprises a set of rotating components, such as a fan, one or more compressors, one or more turbines, an accessory drive unit, etc. Such rotating components require cooling and lubrication by circulating a coolant, usually oil, in contact with the rotating parts.

[0003] As is known, oil heats up upon contact with the rotating parts of rotary components and must itself be cooled. Patent application FR3094753A1 describes the integration of a surface-type heat exchanger on the nacelle of an aircraft turbomachine, comprising a set of channels formed on the wall. The oil, forming the hot source, circulates through the channels and is cooled by convection with the airflow circulating in the secondary channel or outside the nacelle, forming the cold source. Once cooled, the oil is directed back to the rotating components to be cooled and lubricated, in a closed circuit.

[0004] In practice, during an in-flight shutdown of an aircraft turbomachine or during prolonged ground parking in very cold weather, the refrigerant is exposed to extremely low ambient temperatures, making it viscous and potentially causing it to solidify in the surface heat exchanger channels. After the turbomachine restarts, this slows the flow rate or even prevents the circulation of the refrigerant in the surface heat exchanger, thus disrupting the cooling of the aircraft's hot zones.

[0005] To address this, patent application FR3126444A1 describes a method for activating a safe heating device in the presence of very low temperatures. This device takes the form of resistive cables or air ducts extending internally within the channels. This necessitates larger diameter channels to maintain an equivalent flow rate, which increases the mass and size of the surface heat exchanger.

[0006] It is also known from patent application US2024318575A1 a heat exchange system comprising an air-to-oil cooler and a valve releasing air into the cooler upon receipt of a fire signal above a certain temperature.

[0007] The invention thus aims to eliminate at least some of these drawbacks. PRESENTATION OF THE INVENTION

[0008] The invention relates to a refrigerant circuit with integrated drain for an aircraft propulsion assembly, the refrigerant circuit comprising at least one heat exchanger including a wall exposed to an airflow and at least one circulation channel connected to the wall and in which a refrigerant circulates from upstream to downstream so as to be cooled by the airflow, the refrigerant circuit comprising a supply line configured to supply the circulation channel with refrigerant.

[0009] The invention is remarkable in that the refrigerant circuit includes at least one drain line comprising: A reservoir configured to store drain air at a drain pressure, An inlet valve comprising, when the drain pressure is greater than an internal pressure of the refrigerant in the heat exchanger, an open position allowing the drain air stored in the reservoir to flow upstream to downstream in the circulation channel so as to drain the heat exchanger of the refrigerant during a shutdown phase of the aircraft propulsion assembly.

[0010] During an aircraft propulsion system shutdown, the invention allows pressurized air to be released into the heat exchanger, forcing the refrigerant out of the heat exchanger. This prevents the refrigerant from becoming viscous or even solidifying in the circulation channels and disrupting circulation within the refrigerant circuit. The invention is particularly relevant to cases of in-flight shutdown and prolonged ground parking in very cold weather, where the refrigerant is exposed to extremely low temperatures, potentially dropping below -40°C. Furthermore, the heat exchanger features a simpler and less expensive design, eliminating the need for resistive cables or internal piping within the circulation channels.

[0011] According to one aspect of the invention, the heat exchanger is a surface heat exchanger. The heat exchanger is said to be a surface heat exchanger in that the heat exchange takes place on a heat exchange surface formed by the wall on which the circulation channels extend or are fixed. The wall typically takes the form of a portion of the external fairing of the aircraft propulsion assembly, particularly the nacelle, a portion of the external wall of the secondary duct, or a portion of the internal wall of the secondary duct. Such a surface heat exchanger is distinguished, in particular, from a matrix heat exchanger, also known as a volumetric heat exchanger, where the channels extend within the internal volume of an air duct.

[0012] According to another aspect of the invention, the heat exchanger is of the matrix type. Preferably, the matrix heat exchanger comprises a plurality of circulation channels.

[0013] In a preferred design, the heat exchanger wall at least partially encloses the circulation channels. This results in a compact heat exchanger and helps maintain aerodynamics.

[0014] According to another aspect, the circulation channels are fixed to the wall of the heat exchanger.

[0015] According to one aspect of the invention, the drain line reservoir has an internal volume at least equal to the internal volume of the heat exchanger. This allows for the removal of substantially all the refrigerant from the heat exchanger's circulation channels. The risk of blocking the circulation channels due to refrigerant freezing is eliminated.

[0016] According to one aspect of the invention, the inlet valve is in the form of a non-return valve. This allows for passive draining, without intervention or control from an operator or a control system.

[0017] According to one aspect of the invention, the drain line includes a sampling valve mounted upstream of the tank and having, when the external pressure of the refrigerant is greater than the drain pressure, an open position allowing the external drain air to be stored in the tank. This allows the tank to be filled simply and passively during the aircraft's climb, without intervention or command from an operator or a control system.

[0018] According to one aspect of the invention, the refrigerant circuit includes an alarm device configured to alert to the unavailability of the drain line when the drain pressure in the tank is below a predetermined threshold. This allows for the simple and practical detection of a leak and / or malfunction and informs an operator.

[0019] According to one aspect of the invention, said at least one heat exchanger is in the form of a plurality of heat exchangers, and said at least one drain line is in the form of a plurality of drain lines, each associated with one of the plurality of heat exchangers. Each heat exchanger is thus supplied with drain air by a dedicated drain line. Advantageously, each heat exchanger can therefore be drained efficiently and independently, minimizing pressure losses.

[0020] According to one aspect of the invention, the refrigerant circuit includes a drain line configured to guide the refrigerant out of the circulation channel and into contact with at least one area to be cooled within the aircraft propulsion system. The drain line includes a separation line comprising a separator configured to separate the drain air from the refrigerant. Preferably, the separator is in the form of an oil separator. This advantageously allows, after the drain air has been extracted, the refrigerant to be reinjected into the refrigerant reservoir. This limits refrigerant consumption and prevents unwanted losses.

[0021] In a preferred configuration, the drain line includes a deaerator designed to separate the remaining drain air from the refrigerant separator. This advantageously allows the refrigerant to be reinjected into the refrigerant reservoir after the drain air has been extracted. This limits refrigerant consumption and prevents unwanted losses.

[0022] The invention also relates to an aircraft propulsion assembly comprising a refrigerant fluid circuit as described above.

[0023] According to one aspect of the invention, the aircraft propulsion system comprises a cowling mounted on a pivoting axis and over which the heat exchanger circulation channel extends vertically between a high upstream position located on the pivot axis and a low downstream position relative to gravity in nominal operation of the aircraft propulsion system. The cowling includes a removable fluid connection mounted at the low downstream position through which the drain line extends. This reduces the pressure required to vent the refrigerant and / or drain air from the heat exchanger.

[0024] The invention also relates to a method of using an aircraft propulsion system refrigerant circuit as described above, in which, during a shutdown phase of the aircraft propulsion system: The supply line ceases to supply the heat exchanger circulation channel with refrigerant, The internal pressure of the refrigerant in the heat exchanger becomes lower than the drain pressure of the drain air in the tank, which moves the inlet valve from a closed position to the open position, The drain air stored in the tank circulates upstream to downstream in the circulation channel so as to drain the heat exchanger of the refrigerant.

[0025] The invention advantageously eliminates the risk of blockage in the circulation channels due to the refrigerant freezing during an in-flight shutdown. Draining is advantageously implemented passively, requiring no operator input or control device.

[0026] According to one aspect of the invention, the refrigerant circuit drain line includes a sampling valve mounted upstream of the tank and includes, when the external pressure of the refrigerant is greater than the drain pressure, an open position allowing the storage of external drain air in the tank, a method of use in which, during a climb phase of the aircraft propulsion assembly: The supply line supplies the heat exchanger circulation channel with refrigerant, The internal pressure of the refrigerant in the heat exchanger is greater than the drain pressure in the tank which keeps the inlet valve in the closed position, The external pressure of the drain air becomes greater than the drain pressure in the tank which moves the sampling valve from a closed position to the open position, The tank fills with drain air.

[0027] The air tank is advantageously filled in a simple and passive manner during the aircraft's ascent, without intervention or command from an operator or a control system.

[0028] According to one aspect of the invention, during a descent phase of the aircraft propulsion assembly: The supply line supplies the heat exchanger circulation channel with refrigerant, The internal pressure of the refrigerant in the heat exchanger is greater than the drain pressure in the tank which keeps the inlet valve in the closed position, The drain pressure of the drain air stored in the tank becomes greater than the external pressure of the drain air which moves the sampling valve from the open position to the closed position.

[0029] The drain line is advantageously operational from the climb phase, pending a possible in-flight stop. PRESENTATION OF THE FIGURES

[0030] 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.

[0031] Laest is a schematic representation in longitudinal half-section of an aircraft propulsion assembly comprising a refrigerant fluid circuit according to one embodiment of the invention.

[0032] Laest is a schematic representation of the refrigerant circuit according to an embodiment of the invention during a start-up phase of the aircraft propulsion system.

[0033] This is a schematic representation of the coolant circuit during the ascent phase of the aircraft propulsion system.

[0034] This is a schematic representation of the coolant circuit during a descent phase of the aircraft propulsion system.

[0035] This is a schematic representation of the coolant circuit during a shutdown phase of the aircraft propulsion system.

[0036] This is a schematic representation of the coolant circuit during a restart phase of the aircraft propulsion system.

[0037] This is a schematic representation of the method of using the refrigerant circuit according to an embodiment of the invention.

[0038] Laest is a schematic representation of the refrigerant fluid circuit according to another embodiment of the invention.

[0039] Laest is a schematic representation of a refrigerant fluid circuit with two surface heat exchangers mounted in parallel according to another embodiment of the invention.

[0040] It should be noted that the figures explain the invention in detail for implementing the invention, said figures being of course able to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0041] With reference to the, an aircraft comprises one or more propulsion assemblies 30 including a turbomachine 31 and a nacelle 32. The aircraft turbomachine 31 extends along a longitudinal axis X oriented from upstream to downstream and is configured to enable the propulsion of the aircraft from the acceleration of an airflow F circulating from upstream to downstream in the turbomachine 31. The nacelle 32 extends around the turbomachine 31 and guides the airflow F into the turbomachine 31.

[0042] As illustrated in the figure, the aircraft turbomachine 31 comprises a set of rotating components, including a fan 31, one or more compressors 34, 35, one or more turbines 36, 37, an accessory drive housing (not shown) and one or more accessory electric generators (not shown), which are cooled and lubricated by the circulation of a coolant fluid in contact with the rotating portions of the rotating components.

[0043] With reference to Figures 1 and 2, the invention relates to a refrigerant circuit 29 with integrated drain for an aircraft propulsion system 30. The refrigerant circuit (29) according to the invention comprises: a heat exchanger 1 including a wall 2 exposed to an airflow F and one or more circulation channels 3 extending over the wall 2 and in which the refrigerant H, typically oil, flows from upstream to downstream so as to be cooled by the airflow F; a supply line 15 configured to supply the circulation channel 3 with refrigerant H; a drain line 10 including a reservoir 12 configured to store drain air G at a drain pressure Pvid and an inlet valve 13 including, when the drain pressure Pvid is greater than an internal pressure Pint of the refrigerant H in the heat exchanger 1,an open ON position allowing the drain air G stored in the reservoir 12 to circulate from upstream to downstream in the circulation channels 3 so as to drain the heat exchanger 1 of the refrigerant H during a shutdown phase E4 (see) of the aircraft propulsion assembly 30.,

[0044] During a shutdown of the aircraft propulsion system 30, the invention allows pressurized drain air G to be released into the circulation channels 3 of the heat exchanger 1, which has the effect of carrying the refrigerant H from upstream to downstream out of the heat exchanger 1. In other words, the drain air G replaces the refrigerant H in the circulation channels 3 of the heat exchanger 1. This prevents the refrigerant H from becoming viscous or even solidifying in the circulation channels 3 and disrupting circulation in the refrigerant circuit 29. The invention is particularly relevant to cases of in-flight shutdown and prolonged ground parking in very cold weather, where the refrigerant H is exposed to very low temperatures, which can drop below -40°C.The invention also has the advantage of not increasing the dimensions of the heat exchanger 1, unlike prior art solutions incorporating resistive cables or air ducts inside the circulation channels.

[0045] The heat exchanger 1 is typically a surface type, meaning that heat exchange takes place on a heat exchange surface formed by the wall 2, where the circulation channels 3 extend. In the example shown, the surface heat exchanger 1 is formed on the fan casing of the aircraft turbomachine 31, with the wall 2 externally delimiting the secondary duct 38 of the aircraft turbomachine 31. The surface heat exchanger 1 could also be positioned at other locations on the turbomachine 31 or the nacelle 32, preferably in contact with the airflow F circulating in the secondary duct 38 or outside the nacelle 32. Alternatively, the heat exchanger 1 is a volume type, with the circulation channels 3 extending into the internal volume of the air duct.

[0046] With reference to the diagram, the heat exchanger 1 typically comprises several circulation channels 3, an upstream distributor 5, and a downstream manifold 6. The distributor 5 is configured to distribute the refrigerant H into the circulation channels 3. The manifold 6 is configured to collect the refrigerant H at the outlet of the circulation channels 3. The circulation channels 3 extend side by side, in this example transversely to the longitudinal axis X. The circulation channels 3 are connected to the wall 2 and are preferably partially delimited by the wall 2. The circulation channels 3 typically have a U-shaped wall attached to the wall 2, preferably by welding, preferably by friction stir welding. The circulation channels 3 are alternatively attached to the wall 2.The refrigerant fluid H circulates from upstream to downstream in the circulation channels 3 and is cooled by thermal convection with the airflow F flowing along the wall 2.

[0047] With reference to the, the supply line 15 opens into the inlet of the heat exchanger 1, typically in the distributor 5. The supply line 15 typically includes a tank 16, in which the refrigerant H is stored, and a drive pump 17, in particular a positive displacement pump, in particular a high-pressure type, mounted downstream of the tank 16. The drive pump 17 allows the refrigerant H to be driven from upstream to downstream in the supply line 15.

[0048] As illustrated in the figure, the supply line 15 typically also includes a supply valve 18, preferably in the form of a check valve. The supply valve 18, in an open ON position, allows the supply of refrigerant H to the heat exchanger 1, and in a closed OFF position, prevents it.

[0049] With reference to the, the refrigerant circuit 29 typically includes a drain line 20 opening out of the heat exchanger 1, typically into the manifold 6. The drain line 20 typically includes a drain pump 24, configured to drain the refrigerant H out of the heat exchanger 1 and carry it upstream to downstream in the drain line 20. The drain line 20 is typically configured to circulate in the areas to be cooled 22 of the aircraft propulsion assembly 30, in particular in contact with the rotating parts of the rotating components of the aircraft turbomachine 31, in particular the rotary bearings.

[0050] As illustrated in the figure, the drain line 20 typically also includes a drain valve 21, preferably in the form of a check valve. The drain valve 21, in an open (ON) position, allows the refrigerant H to drain into the drain line 20, and in a closed (OFF) position, prevents it.

[0051] With further reference to the drain line 20, the outlet of the supply line 15 connects to the reservoir 16, thus forming a closed circuit. A deaerator 24 is typically mounted upstream of the reservoir 16 and is configured to separate the air from the refrigerant H, the air being introduced into the circuit, particularly at the bearings of the areas to be cooled 22.

[0052] According to a preferred aspect illustrated in the figure, the drain line 10 comprises, from upstream to downstream, a drain air sampling valve 11, preferably preceded by a pressure relief valve, a drain air storage tank 12, and a drain air inlet valve 13 for the drain air into the heat exchanger 1. The sampling valve 11, in its open (ON) position, allows the drain air G to be drawn from outside and stored in the tank 12, and in its closed (OFF) position, prevents it from entering. The drain line 10 typically terminates upstream at the blower 33, downstream of a stage of the low-pressure compressor 34 or the secondary line 38, to draw the external drain air G at a temperature below 150°C and at a pressure sufficient to at least compensate for the hydrostatic pressure of the refrigerant H to be discharged from the heat exchanger 1.

[0053] Preferably, the sampling valve 11 and the inlet valve 13 are in the form of check valves. Such passive valves advantageously allow for emptying without operator intervention or control system intervention. Alternatively, the drain line 10 could be without a sampling valve 11, the tank 12 being pre-filled with pressurized drain air G before use. However, this requires on-site operator intervention.

[0054] Preferably also, the reservoir 12 of the drain line 10 has an internal volume V12 at least equal to the internal volume V1 of the heat exchanger 1. Thus during draining, the drain air G can replace the refrigerant H throughout the heat exchanger 1.

[0055] Preferably, an alert device 14 is configured to alert an operator, for example visually or audibly, to the unavailability of the drain line 10 when the drain pressure Pvid in the tank 12 is below a predetermined threshold.

[0056] According to a preferred aspect illustrated in the figure, the drain line 20 includes a separation line 25 configured to drain the mixture of refrigerant H and drain air G to an air-oil separator 23, typically an oil separator, for example mounted on the accessory relay box of the aircraft turbomachine 31. The air-oil separator 23 separates the drain air G and the refrigerant H. The drain air G is discharged to the outside while the refrigerant H is guided to the reservoir 16 of the supply line 15, and preferably via the deaerator 24 separating the drain air G remaining in the refrigerant H.

[0057] In the example shown, the separation line 25 terminates upstream at the outlet of the cooling zones 22, specifically in the rotating bearing enclosures. Also in this example, the separation line 25 terminates downstream in the discharge line 20 upstream of the deaerator 24.

[0058] In the example of the, the heat exchanger 1 is formed on a cowl 28 of pivot axis Y of the aircraft propulsion assembly 30. The circulation channels 3 of the heat exchanger 1 extend vertically between a high upstream position Y5 located on the pivot axis Y and a low downstream position Y6 with respect to gravity G, in a nominal use of the aircraft propulsion assembly 30.

[0059] Preferably, as illustrated in the figure, the hood 28 includes a removable fluid connection 27 mounted at the lower downstream position Y6 through which the drain line 20 extends. The fluid connection 27 is removable in that it can be opened when the hood 28 is open and closed when the hood 28 is closed. Thanks to the fluid connection 27, the drain line 20 can reach the areas to be cooled 22 at the lower downstream position Y6, thereby reducing the drain air pressure G required in the heat exchanger 1 to perform the purge.

[0060] Alternatively, the discharge line 20 extends from the lower downstream position Y6 to the upper upstream position Y5 where the pivot axis Y of the hood 28 is located to reach the areas to be cooled 22. This avoids the integration of a removable fluid connection 27.

[0061] Figure 1 illustrates an embodiment in which the refrigerant circuit 29 comprises several heat exchangers 1 mounted in parallel, typically with a common supply line 15 and a common drain line 20. Preferably, each heat exchanger 1 is supplied with drain air G via a dedicated drain line G. This ensures efficient and independent draining for each heat exchanger 1.

[0062] With reference to the, a method for using the refrigerant circuit 29 consists of: During a start-up phase E1 of the aircraft propulsion system 30, starting the circulation of the refrigerant H in the heat exchanger 1; During a climb phase E2 of the aircraft propulsion system 30, filling the reservoir 12 with drain air G in the drain line 10, with the refrigerant H circulating in the heat exchanger 1; During a cruise and descent phase E3 of the aircraft propulsion system 30, maintaining the drain air G under pressure in the reservoir 12, with the refrigerant H circulating in the heat exchanger 1; During a shutdown phase E4 of the aircraft propulsion system 30, releasing the drain air G from the drain line 10 into the heat exchanger 1 to drain the fluid refrigerant H, and during a restart phase E5 of the aircraft propulsion system 30,to restart the circulation of the refrigerant fluid H in the heat exchanger 1 in order to purge the drain air G present in the heat exchanger 1.

[0063] In the example above, the E4 shutdown phase occurs after a descent phase E3 and corresponds to the case of an in-flight shutdown during descent or a prolonged ground stop in very cold weather. However, it goes without saying that the E4 shutdown phase could also occur after a climb phase E2, in the case of an in-flight shutdown during climb or during the cruise phase of the aircraft propulsion system 30.

[0064] As illustrated in the figure, during the E1 start-up phase of the aircraft propulsion system 30, the drive pump 17 draws the refrigerant H into the supply line 15. The pressure in the supply line 15 becomes greater than the pressure Pint in the heat exchanger 1, which moves the supply valve 18 to the open ON position, allowing the admission of refrigerant H into the heat exchanger 1. The drain valve 21 is in the open ON position and allows the refrigerant H to be discharged into the drain line 20. The drain line 10 is in an inactive state A: the sampling valve 11 and the inlet valve 13 are in the closed OFF position, the tank 12 being discharged.

[0065] Figure 1 illustrates the climb phase E2, which includes takeoff and ascent. The climb phase E2 differs from the start-up phase E1 in that the external pressure Pext becomes greater than the drain pressure Pvid in tank 12, which moves the intake valve 11 to the open ON position. Drain air G is drawn from outside and fills tank 12. The internal pressure Pint of the refrigerant H in the heat exchanger 1 is greater than the drain pressure Pvid in tank 12, which keeps the intake valve 13 in the closed OFF position.

[0066] This illustrates the descent phase E3, including landing and taxiing. The descent phase E3 differs from the climb phase E2 in that the external pressure Pext becomes lower than the drain pressure Pvid in tank 12, which moves the bleed valve 11 to the closed OFF position. Thus, at the end of the climb phase E2, tank 12 is full and the drain line 10 is in a standby state B, ready to perform a drain in the event of an in-flight shutdown of the propulsion system 30.

[0067] Figure 1 illustrates a shutdown phase E4 of the propulsion assembly 30, where the supply line 15 ceases to supply the circulation channels 3 of the heat exchanger 1 with refrigerant H. The internal pressure Pint of the refrigerant H in the heat exchanger 1 becomes lower than the drain pressure Pvid of the drain air G in the reservoir 12, which moves the inlet valve 13 to the open ON position. The drain line 10 is thus in an active state C, releasing the drain air G from the reservoir 12 into the circulation channels 3. The pressurized drain air G guides the refrigerant H out of the heat exchanger 1. At the end of the shutdown phase E4, the drain air G has substantially replaced the refrigerant H in the circulation channels 3. The risk of blocking circulation in the circulation channels 3 due to the refrigerant H freezing is thus eliminated.

[0068] The E5 restart phase is distinguished from the E1 start-up phase in that the refrigerant H admitted by the supply line 15 guides the drain air G present in the circulation channels 3 out of the heat exchanger 1. Phases E2, E3, E4 can be implemented again after phase E5.

[0069] The invention advantageously eliminates the risk of blockage in the circulation channels 3 due to the freezing of the refrigerant H during an in-flight shutdown. Draining is advantageously implemented passively, requiring no operator intervention or control device. Furthermore, the heat exchanger 1 has a simpler and less expensive design, eliminating the need for resistive cables or internal conduits within the circulation channels 3.

Claims

A refrigerant circuit (29) with integrated drain for an aircraft propulsion system (30), the refrigerant circuit (29) comprising at least one heat exchanger (1) having a wall (2) exposed to an airflow (F) and at least one circulation channel (3) connected to the wall (2) and through which a refrigerant (H) flows from upstream to downstream so as to be cooled by the airflow (F), the refrigerant circuit (29) comprising a supply line (15) configured to supply the circulation channel (3) with refrigerant (H), the refrigerant circuit (29) being characterized in that it comprises at least one drain line (10) comprising: A reservoir (12) configured to store drain air (G) at a drain pressure (Pvid), the reservoir (12) having an internal volume (V12) at least equal to an internal volume (V1) of the heat exchanger (1), An inlet valve (13) comprising,when the drain pressure (Pvid) is greater than an internal pressure (Pint) of the refrigerant (H) in the heat exchanger (1), an open position (ON) allows the drain air (G) stored in the reservoir (12) to flow upstream to downstream in the circulation channel (3) so as to drain the heat exchanger (1) of the refrigerant (H) during a shutdown phase (E4) of the aircraft propulsion system (30). Refrigerant fluid circuit (29) according to claim 1, wherein the heat exchanger (1) is surface-based. Refrigerant circuit (29) according to any one of claims 1 and 2, wherein the drain line (10) includes a sampling valve (11) mounted upstream of the reservoir (12) and comprising, when the external pressure (Pext) of the refrigerant (H) is greater than the drain pressure (Pvid), an open position (ON) allowing the storage of external drain air (G) in the reservoir (12). Refrigerant fluid circuit (29) according to any one of claims 1 to 3, comprising an alarm device (14) configured to alert on the unavailability of the drain line (10) when the drain pressure (Pvid) in the tank (12) is below a predetermined threshold. Refrigerant circuit (29) according to any one of claims 1 to 4, wherein said at least one heat exchanger (1) is in the form of a plurality of heat exchangers (1) and said at least one drain line (10) is in the form of a plurality of drain lines (10) each associated with one of the plurality of heat exchangers (1). Refrigerant circuit (29) according to any one of claims 1 to 5, comprising a drain line (20) configured to guide the refrigerant (H) out of the circulation channel (3) into contact with at least one area to be cooled (22) of the aircraft propulsion assembly (30), the drain line (20) comprising a separation line (25) comprising a separator (23) configured to separate the drain air (G) from the refrigerant (H). Aircraft propulsion assembly (30) comprising a refrigerant fluid circuit (29) according to claim 6, the aircraft propulsion assembly (30) comprising a cowl (28) mounted on a pivot axis (Y) and on which extends vertically the circulation channel (3) of the heat exchanger (1) between a high upstream position (Y5) located on the pivot axis (Y) and a low downstream position (Y6) relative to gravity (G) in a nominal use of the aircraft propulsion assembly (30), the cowl (28) comprising a removable fluid fitting (27) mounted at the low downstream position (Y6) through which extends the drain line (20). A method of using a refrigerant circuit (29) of an aircraft propulsion assembly (30) according to any one of claims 1 to 7, wherein, during a shutdown phase (E4) of the aircraft propulsion assembly (30): The supply line (15) ceases to supply the circulation channel (3) of the heat exchanger (1) with refrigerant (H), The internal pressure (Pint) of the refrigerant (H) in the heat exchanger (1) becomes less than the drain pressure (Pvid) of the drain air (G) in the reservoir (12), which moves the inlet valve (13) from a closed position (OFF) to the open position (ON), The drain air (G) stored in the reservoir (12) flows upstream to downstream in the circulation channel (3) so as to drain the heat exchanger (1) of the refrigerant (H). A method of use according to claim 8, the drain line (10) of the refrigerant circuit (29) comprising a sampling valve (11) mounted upstream of the reservoir (12) and comprising, when the external pressure (Pext) of the drain air (G) is greater than the drain pressure (Pvid), an open position (ON) allowing the storage of the external drain air (G) in the reservoir (12), a method of use in which, during a climb phase (E2) of the aircraft propulsion assembly (30): The supply line (15) supplies the circulation channel (3) of the heat exchanger (1) with refrigerant (H), The internal pressure (Pint) of the refrigerant (H) in the heat exchanger (1) is greater than the drain pressure (Pvid) in the reservoir (12) which keeps the inlet valve (13) in the closed position (OFF),The external pressure (Pext) of the drain air (G) becomes greater than the drain pressure (Pvid) in the tank (12), which moves the sampling valve (11) from a closed (OFF) position to an open (ON) position. The tank fills with drain air (G).

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