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

Abstract

A refrigerant circuit (29) for an aircraft propulsion system comprising: - a heat exchanger (1) including a circulation channel (3) for a refrigerant (H); - 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 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 position (ON) allowing the drain air 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 an in-flight shutdown of the aircraft propulsion system. Figure from the summary: Figure 2

Description

Title of the invention: Refrigerant fluid circuit for an aircraft propulsion system and its method of use. Technical field

[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 housing, etc. Such rotating components require cooling and lubrication by circulating a coolant, usually oil, in contact with the rotating portions.

[0003] As is known, oil heats up upon contact with the rotating parts of rotating components and must itself be cooled. French 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 in 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 the aircraft turbomachine or during prolonged ground parking in very cold weather, the refrigerant is exposed to very low ambient temperatures, making it viscous and even liable to solidify in the channels of the surface heat exchanger. After restarting the turbomachine, this slows the flow rate or even prevents the circulation of the refrigerant in the surface heat exchanger, thus disrupting the cooling of the hot zones of the aircraft turbomachine.

[0005] To remedy this, patent application FR3126444A1 discloses a method for activating a safe heating device in the presence of very low temperatures, which 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] The invention thus aims to eliminate at least some of these drawbacks. PRESENTATION OF THE INVENTION

[0007] The invention relates to a refrigerant circuit with integrated drain for an aircraft propulsion system, the refrigerant circuit comprising at least one heat exchanger comprising a wall exposed to an airflow and at least one circulation channel connected to the wall and in which a refrigerant fluid circulates from upstream to downstream so as to be cooled by the airflow, the refrigerant fluid circuit comprising a supply line configured to supply the circulation channel with refrigerant fluid.

[0008] 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 tank to circulate 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 system.

[0009] 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 in 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 very low temperatures, which can drop below -40°C. Furthermore, the heat exchanger has a simpler and less expensive design, eliminating the need for resistive cables or internal pipes in the circulation channels.

[0010] 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, in particular 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.

[0011] 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.

[0012] According to a preferred aspect, the wall of the heat exchanger at least partially delimits the circulation channels. The heat exchanger thus has a small footprint and helps to preserve aerodynamics.

[0013] According to another aspect, the circulation channels are fixed to the wall of the heat exchanger.

[0014] 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 the refrigerant freezing is eliminated.

[0015] 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 by an operator or a control system.

[0016] 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 makes it possible to fill the tank simply and passively during the aircraft's climb, without intervention or command from an operator or a control system.

[0017] 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.

[0018] 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 thus be drained efficiently and independently, limiting pressure losses.

[0019] According to one aspect of the invention, the refrigerant circuit comprises a drain line configured to guide the refrigerant out of the circulation channel into contact with at least one area to be cooled of the aircraft propulsion assembly. The drain line comprises a separation line including 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 extraction The drain air is then recirculated back into the refrigerant reservoir. This limits refrigerant consumption and prevents unwanted losses.

[0020] According to a preferred aspect, the drain line includes a deaerator configured to separate the drain air remaining at the outlet of the refrigerant separator. This advantageously allows, after extraction of the drain air, the refrigerant to be reinjected into the refrigerant reservoir. This limits refrigerant consumption and prevents unwanted losses.

[0021] The invention also relates to an aircraft propulsion assembly comprising a refrigerant fluid circuit as described above.

[0022] According to one aspect of the invention, the aircraft propulsion assembly 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 assembly. 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.

[0023] The invention also relates to a method of using an aircraft propulsion system coolant 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 an open position. • The drain air stored in the tank circulates from upstream to downstream in the circulation channel so as to drain the heat exchanger of the refrigerant.

[0024] The invention advantageously eliminates the risk of blocking circulation 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.

[0025] According to one aspect of the invention, the refrigerant circuit drain line includes a sampling valve mounted upstream of the reservoir 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 system: • The supply line feeds the heat exchanger circulation channel with refrigerant, • The internal pressure of the refrigerant in the heat exchanger is higher 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 dispensing valve from a closed position to an open position. • The tank fills with drain air.

[0026] 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.

[0027] According to one aspect of the invention, during a descent phase of the aircraft propulsion system: • The supply line feeds the heat exchanger circulation channel with refrigerant, • The internal pressure of the refrigerant in the heat exchanger is higher 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 drain air pressure, which moves the sampling valve from the open position to the closed position.

[0028] The drain line is advantageously operational from the climb phase, pending a possible stop in flight. PRESENTATION OF THE FIGURES

[0029] 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.

[0030] Fig. 1 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.

[0031] Figure 2 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.

[0032] Fig. 3 is a schematic representation of the coolant circuit of Fig. 2 during a climb phase of the aircraft propulsion assembly.

[0033] Fig. 4 is a schematic representation of the coolant circuit of Fig. 2 during a descent phase of the aircraft propulsion assembly.

[0034] Fig. 5 is a schematic representation of the coolant circuit of Fig. 2 during a shutdown phase of the aircraft propulsion system.

[0035] Fig. 6 is a schematic representation of the coolant circuit of Fig. 2 during a restart phase of the aircraft propulsion system.

[0036] Fig. 7 is a schematic representation of the method of using the refrigerant circuit according to an embodiment of the invention.

[0037] Fig. 8 is a schematic representation of the refrigerant circuit according to another embodiment of the invention.

[0038] Fig. 9 is a schematic representation of a refrigerant fluid circuit with two surface heat exchangers mounted in parallel according to another embodiment of the invention.

[0039] 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

[0040] With reference to [Fig. 1], 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 in the turbomachine 31.

[0041] As illustrated in [Fig.1], 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 circulating a coolant fluid in contact with the rotating portions of the rotating components.

[0042] 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 comprising a wall 2 exposed to an airflow F and one or more circulation channels 3 extending over the wall 2 and into which circulates the refrigerant fluid H, typically oil, 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 fluid H, • a drain line 10 comprising a reservoir 12 configured to store drain air G at a drain pressure Pvid and 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 allowing the drain air G stored in the reservoir 12 to flow 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 [Fig. 5]) of the aircraft propulsion assembly 30.

[0043] During a shutdown of the aircraft propulsion assembly 30, the invention makes it possible to release pressurized drain air G 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. Furthermore, the invention 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.

[0044] 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 of [Fig. 1], the surface heat exchanger 1 is formed on the fan casing of the aircraft turbomachine 31, 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.

[0045] With reference to [Fig. 2], 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 channels of Circulation 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 H flows from upstream to downstream in the circulation channels 3 and is cooled by thermal convection with the airflow F flowing along the wall 2.

[0046] With reference to [Fig.2], 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 reservoir 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 reservoir 16. The drive pump 17 allows the refrigerant H to be driven from upstream to downstream in the supply line 15.

[0047] As illustrated in [Fig. 2], 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.

[0048] With reference to [Fig.2], 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.

[0049] As illustrated in [Fig. 2], 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.

[0050] With further reference to [Fig. 2], the discharge line 20 opens into the reservoir 16 of the supply line 15, 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 fluid H, the air being introduced into the circuit particularly at the level of the bearings of the areas to be cooled 22.

[0051] According to a preferred aspect illustrated in [Fig.2], the drain line 10 comprises, from upstream to downstream, a drain air sampling valve 11 G, preferably preceded by a pressure relief valve, a drain air storage tank 12 G and a drain air inlet valve 13 G into the heat exchanger 1. The sampling valve 11, in an open ON position, allows the drain air G to be drawn from outside and stored in the tank 12, and in a closed OFF position, prevents it. The drain line 10 typically opens upstream at the blower 33, downstream of a stage of the low pressure compressor 34 or of the secondary line 38 to draw in outside drain air G at a temperature below 150°C and at a pressure sufficient to compensate at least the hydrostatic pressure of the refrigerant H to be evacuated from the heat exchanger 1.

[0052] Preferably, the sampling valve 11 and the inlet valve 13 are in the form of check valves. Such passive valves advantageously allow emptying to be carried out without control or intervention from an operator or a control system. 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 intervention by an operator.

[0053] Preferably also, the reservoir 12 of the drain line 10 has an internal volume V12 at least equal to the internal volume VI of the heat exchanger 1. Thus during draining, the drain air G can replace the refrigerant H throughout the heat exchanger 1.

[0054] 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.

[0055] According to a preferred aspect illustrated in [Fig. 2], 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 allows the drain air G and the refrigerant H to be separated. 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.

[0056] In the example of [Fig.2], the separation line 25 opens upstream at the outlet of the areas to be cooled 22, in particular in the enclosures of the rotating bearings. Still in this example, the separation line 25 opens, downstream, into the evacuation line 20 upstream of the deaerator 24.

[0057] In the example of [Fig.8], the heat exchanger 1 is formed on a cowling 28 with 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 nominal use of the aircraft propulsion assembly 30.

[0058] Preferably, as illustrated in [Fig. 8], 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.

[0059] 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.

[0060] Figure 9 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.

[0061] With reference to [Fig.7], one method of using the refrigerant circuit 29 consists of: • During a start-up phase El of the aircraft propulsion system 30, to start the circulation of the refrigerant fluid H in the heat exchanger 1, • During a climb phase E2 of the aircraft propulsion system 30, to fill the tank 12 with drain air G in the drain line 10, the refrigerant H circulating in the heat exchanger 1, • During a cruise and descent phase E3 of the aircraft propulsion system 30, to maintain the drain air G under pressure in the tank 12, the refrigerant H circulating in the heat exchanger 1, • During a shutdown phase E4 of the aircraft propulsion system 30, to release the drain air G from the drain line 10 into the heat exchanger 1 to drain the refrigerant H, and • During a restart phase E5 of the aircraft propulsion assembly 30, to restart the circulation of the refrigerant fluid H in the heat exchanger 1 to purge the drain air G present in the heat exchanger 1.

[0062] In the example of [Fig. 7], the stopping phase E4 occurs after a descent phase E3 and corresponds to the case of an in-flight stop during descent or a prolonged ground stop in very cold weather. It is understood, however, that the stopping phase E4 could occur after a climb phase E2, in the case of an in-flight stop during climb or during the cruise regime of the aircraft propulsion system 30.

[0063] As illustrated in [Fig. 2], during the start-up phase El 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 refrigerant H to be admitted 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 reservoir 12 being discharged.

[0064] Figure 3 illustrates the climb phase E2, including 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 the tank 12, which moves the intake valve 11 to the open ON position. Drain air G is drawn from the outside and fills the tank 12. The internal pressure Pint of the refrigerant H in the heat exchanger 1 is greater than the drain pressure Pvid in the tank 12, which keeps the inlet valve 13 in the closed OFF position.

[0065] Figure 4 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 the tank 12, which moves the bleed valve 11 to the closed OFF position. Thus, at the end of the climb phase E2, the 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.

[0066] Figure 5 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 tank 12, which moves the inlet valve 13 into the position open ON. 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.

[0067] Fig. 6 illustrates the restart phase E5, which differs from the start-up phase E1 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.

[0068] The invention advantageously eliminates the risk of blocking circulation in the circulation channels 3 due to the refrigerant H freezing during an in-flight stop. Draining is advantageously implemented passively, requiring no operator input 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

Demands

1. A refrigerant circuit (29) with integrated drain for an aircraft propulsion system (30), the refrigerant circuit (29) comprising at least one heat exchanger (1) including 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) including a supply line (15) configured to supply the circulation channel (3) with refrigerant (H), the refrigerant circuit (29) being characterized in that it includes at least one drain line (10) comprising: • A reservoir (12) configured to store drain air (G) at a drain pressure (Pvid), • 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).

2. Refrigerant fluid circuit (29) according to claim 1, wherein the reservoir (12) of the drain line (10) has an internal volume (V12) at least equal to an internal volume (VI) of the heat exchanger (1).

3. Refrigerant fluid circuit (29) according to any one of claims 1 and 2, wherein the heat exchanger (1) is surface-type.

4. Refrigerant circuit (29) according to any one of claims 1 to 3, wherein the drain line (10) includes a sampling valve (11) mounted upstream of the reservoir (12) and including, when the external pressure (Pext) of the refrigerant (H) is greater than the drain pressure (Pvid), an open position (ON) permitting the storage of external drain air (G) in the reservoir (12).

5. Refrigerant circuit (29) according to any one of claims 1 to 4, 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.

6. Refrigerant circuit (29) according to any one of claims 1 to 5, 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).

7. Refrigerant circuit (29) according to any one of claims 1 to 6, 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).

8. Aircraft propulsion assembly (30) comprising a refrigerant fluid circuit (29) according to claim 7, 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 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).

9. A method of using a refrigerant circuit (29) of an aircraft propulsion system (30) according to any one of claims 1 to 8, wherein, during a shutdown phase (E4) of the aircraft propulsion system (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 lower than the pressure

10. draining (Pvid) of the drain air (G) into 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) circulates from upstream to downstream in the circulation channel (3) so as to drain the heat exchanger (1) of the refrigerant (H). Method of use according to claim 9, 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), 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 tank (12), which keeps the inlet valve (13) in the closed (OFF) position. • 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 position (OFF) to the open position (ON), • The tank fills with drain air (G).

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