HOUSING SYSTEM WITH HEAT EXCHANGER FOR HEATING DIHYDROGEN

Description

TECHNICAL FIELD

[0001] The present invention relates to a housing system containing a heat exchanger which makes it possible to heat dihydrogen passing through said heat exchanger, as well as to an aircraft comprising such a housing system. STATE OF THE PRIOR ART

[0002] In order to reduce kerosene consumption in aircraft engines, it is known to use dihydrogen as fuel. The aircraft then has a main fuel system that includes tanks of liquid dihydrogen. To be used by the engines, dihydrogen must be in gaseous form and for this, the main fuel system includes heat exchangers that ensure the heating of dihydrogen from a hot heat transfer fluid. To bring dihydrogen from the tank to the engine, the main fuel system includes a network of pipes, pumps and valves that goes from the tanks to the engines via the heat exchangers.

[0003] To limit the risk of incidents related to the use of dihydrogen, safety systems are implemented around heat exchangers. Although the systems currently in place are effective, new arrangements that are particularly simple to implement need to be found.

[0004] A housing system according to the state of the art is known from FR 3 110 938 A1. STATEMENT OF THE INVENTION

[0005] An object of the present invention is to propose according to claim 1, a housing system containing a heat exchanger which makes it possible to heat dihydrogen passing through said heat exchanger to power an aircraft engine for example.

[0006] For this purpose, a housing system is proposed intended to be between a supply pipe and a discharge pipe in which a heat transfer fluid circulates, said housing system comprising: a sealed housing divided by a sealed separating wall into a first volume and a second volume filled with a gas inert with respect to dihydrogen, a vacuum pump fluidically connected to the first volume and configured to, in operation, create a vacuum in the first volume, an upstream pipe along which an upstream solenoid valve is mounted and intended to be fluidically connected to a dihydrogen tank, a downstream pipe along which a downstream solenoid valve is mounted and intended to be fluidically connected to an engine, a heat exchanger fixed inside the housing through the separating wall, which has a first inlet fluidically connected to the upstream pipe downstream of the upstream solenoid valve and a first outlet fluidically connected to the downstream pipe upstream of the downstream solenoid valve,and which has a second inlet intended to be fluidically connected to the supply pipe and a second outlet intended to be fluidically connected to the discharge pipe, where the first inlet is arranged in the first volume and the first outlet is arranged in the second volume, a first pressure sensor arranged in the first volume, a second pressure sensor arranged in the second volume, a control unit arranged to receive values ​​of the pressures measured by the pressure sensors, to detect, on the one hand, whether the difference in absolute value between two successive values ​​of the pressure in the first volume is less than a first threshold or greater than a second threshold which is greater than or equal to the first threshold, and on the other hand,if the difference in absolute value between two successive values ​​of the pressure in the second volume is less than another first threshold or greater than another second threshold which is greater than or equal to said other first threshold, and to close the solenoid valves, if it detects a difference in absolute value between two successive pressure values ​​beyond the second threshold in the first volume or said other second threshold in the second volume.

[0007] Such a housing system allows the housing to be isolated in the event of a leak.

[0008] Advantageously, the housing comprises, at the level of a wall of said first volume, a pressure relief valve.

[0009] Advantageously, the housing comprises at a wall of said second volume, an inlet intended to be fluidically connected to a source of inert gas under pressure.

[0010] Advantageously, the housing comprises at a wall of said second volume, an outlet through which the gas can be evacuated.

[0011] According to a particular embodiment, the separating wall comprises a rim secured to the walls of the housing and extending inside the first volume, a central wall extending around the heat exchanger and secured to the latter, and a junction wall extending between the rim and the central wall, fixed in abutment against a face of the rim facing the second volume and in abutment against a face of the central wall facing the second volume.

[0012] According to another particular embodiment, the separating wall comprises a rim secured to the walls of the housing and extending inside the first volume and a central wall extending around the heat exchanger and secured to the latter, where the central wall is fixed in abutment against a face of the rim oriented towards the second volume. Advantageously, the housing system comprises for each volume, at least one additional sensor among a dihydrogen sensor and a dioxygen sensor, arranged in said volume, and the control unit is arranged to receive additional values ​​of the pressures measured by each additional sensor, to compare each additional value thus received with an additional threshold, and to close the solenoid valves if an additional value is greater than said additional threshold.

[0013] The invention also provides an aircraft according to claim 8, comprising: a hydrogen tank, an engine, a housing system according to one of the preceding variants, where the upstream pipe extends between the tank and the first inlet of the heat exchanger, where the downstream pipe extends between the first outlet of the heat exchanger and the engine, and a heat transfer fluid circuit comprising a supply pipe fluidically connected to the second inlet of the heat exchanger and a discharge pipe fluidically connected to the second outlet of the heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above-mentioned and other features of the invention will become more clearly apparent from the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which: Fig. 1 is a top view of an aircraft according to the invention, Fig. 2 is a schematic representation of a housing system according to a first embodiment of the invention, and Fig. 3 is a schematic representation of a housing system according to a second embodiment of the invention. DETAILED PRESENTATION OF EMBODIMENT METHODS

[0015] In the following description, terms relating to a position are taken with reference to an aircraft in a normal flight position, that is to say as represented on the Fig. 1 .

[0016] In the following description, and by convention, we call X the longitudinal direction of the aircraft, we call Y the transverse direction which is horizontal when the aircraft is on the ground, and Z the vertical direction which is vertical when the aircraft is on the ground, these three directions X, Y and Z being orthogonal to each other.

[0017] There Fig. 1 shows an aircraft 100 which comprises a fuselage 102 on each side of which is fixed a wing 104 which carries at least one engine 106 operating with gaseous dihydrogen, in particular at 300K, as fuel. In the embodiment of the invention presented in the Fig. 1 The 106 engine is a propeller engine, but any other type of engine is possible.

[0018] Arrow 107 indicates the forward direction of aircraft 100.

[0019] The aircraft 100 comprises a tank 110 in which the dihydrogen is stored in liquid form, in particular at 30K. In the embodiment of the invention, the tank 110 is arranged at the rear of the fuselage 102, but a different positioning is possible.

[0020] The “upstream” and “downstream” positions are understood relative to the direction of flow of the fluid. The aircraft 100 also comprises a distribution system 112 comprising, among other things, a pipe 116 which fluidically connects the tank to the engine 106. The distribution system 112 also comprises a pump 114 mounted on the pipe 116 to drive the hydrogen leaving the tank 110 in the pipe 116 towards the engine 106.

[0021] Before reaching the engine 106, the dihydrogen passes into a housing system 120 according to the invention and which comprises the pipe 116 which supplies the engine 106. The pipe 116 is thus divided into an upstream pipe 116a which extends between the tank 110 and a first inlet of the housing system 120 and a downstream pipe 116b which extends between a first outlet of the housing system 120 and the engine 106.

[0022] The housing system 120 comprises the upstream pipe 116a along which is mounted an upstream solenoid valve 122a and the downstream pipe 116b along which is mounted a downstream solenoid valve 122b and the solenoid valves 122a-b are thus upstream of the first inlet and downstream of the first outlet of the housing system 120. When the solenoid valves 122a-b are open, the hydrogen arrives at the upstream solenoid valve 122a, passes through the housing system 120 and exits at the downstream solenoid valve 122b to supply the engine 106. When the upstream solenoid valve 122a is closed, the hydrogen does not arrive at the housing system 120 and when the downstream solenoid valve 122b is closed, the hydrogen does not leave the housing system 120.

[0023] There Fig. 2 shows the housing system 220 according to a first embodiment and the Fig. 3 shows the housing system 320 according to a second embodiment.

[0024] The housing system 220, 320 comprises a sealed housing 222 which here consists of side walls 224, a first end wall 226 and a second end wall 228 which are fixed together in a sealed manner to delimit an interior volume 230a-b.

[0025] The housing system 220, 320 comprises a dividing wall 234, 334 which is integral with the walls, here the side walls 224, and which separates the interior volume 230a-b into a first volume 230a between the dividing wall 234, 334 and the first end wall 226 and into a second volume 230b between the dividing wall 234, 334 and the second end wall 228.

[0026] The separating wall 234, 334 forms a sealed barrier between the two volumes 230a and 230b and can take different forms, a first example of which is shown in the Fig. 2 and a second example is shown on the Fig. 3 The housing 222 is thus divided by the dividing wall 234, 334 into a first volume 230a and a second volume 230b.

[0027] The housing system 220, 320 also includes a vacuum pump 250 fluidically connected to the first volume 230a and which, in operation, is arranged to create a vacuum in the first volume 230a. Thus, gases are extracted from the first volume 230a where the vacuum is created and the pressure is reduced therein.

[0028] The second volume 230b is filled with a gas that is inert to dihydrogen, particularly in liquid form, meaning that it does not present any danger when mixed with dihydrogen. The inert gas is, for example, nitrogen.

[0029] The housing system 220, 320 comprises a heat exchanger 232 which is fixed inside the housing 222 and which ensures the heating of the dihydrogen in particular from 30K to 300K. The heat exchanger 232 comprises a first inlet 236a fluidically connected to the upstream pipe 116a downstream of the upstream solenoid valve 122a and a first outlet 238a fluidically connected to the downstream pipe 116b upstream of the downstream solenoid valve 122b. The dihydrogen therefore arrives in the heat exchanger 232 via the first inlet 236a and leaves heated via the first outlet 238a.

[0030] The first inlet 236a is arranged in the first volume 230a and the first outlet 238a is arranged in the second volume 230b, and the heat exchanger 232 therefore passes through the separating wall 234, 334 in a sealed manner. There is therefore a first part of the heat exchanger 232 located in the first volume 230a and a second part of the heat exchanger 232 located in the second volume 230b.

[0031] To reach the first inlet 236a, the upstream pipe 116a passes in a sealed manner through a wall, here a side wall 224, of the housing 222 and in the same way, to reach the first outlet 238a, the downstream pipe 116b passes in a sealed manner through a wall, here a side wall 224, of the housing 222.

[0032] The heat exchanger 232 comprises a second inlet 236b fluidically connected to a supply pipe 240 and a second outlet 238b fluidically connected to a discharge pipe 242. The supply pipe 240 and the discharge pipe 242 respectively ensure the supply of the heat exchanger 232 with heat transfer fluid and the discharge of the heat exchanger 232 with the heat transfer fluid.

[0033] The supply line 240 and the discharge line 242 are part of a heat transfer fluid circuit also comprising a tank in which the heat transfer fluid is stored, a heating system which heats the heat transfer fluid and at least one pump which creates a flow of heat transfer fluid. The heat transfer fluid is driven by the pump in the supply line 240 from the tank to the second inlet 236b passing through the heating system, then after passing through the heat exchanger 232, the heat transfer fluid returns to the tank via the discharge line 242.

[0034] Preferably, the heat transfer fluid is a fluid which does not present any danger when mixed with dihydrogen, such as for example dinitrogen N 2 at 743K.

[0035] In the embodiments of the invention presented to the Figs. 2and3, the second inlet 236b and the second outlet 238b are arranged in the second volume 230b, but a different arrangement is possible.

[0036] To reach the second inlet 236b, the supply pipe 240 passes in a sealed manner through a wall, here a side wall 224, of the housing 222 and in the same way, to reach the second outlet 238b, the discharge pipe 242 passes in a sealed manner through a wall, here a side wall 224, of the housing 222.

[0037] The heat exchanger 232 thus ensures an exchange of calories between the heat transfer fluid which cools and the dihydrogen which heats up.

[0038] The housing system 220, 320 also comprises in the first volume 230a, a first pressure sensor 244a and in the second volume 230b, a second pressure sensor 244b. The first pressure sensor 244a determines the pressure in the first volume 230a and the second pressure sensor 244b determines the pressure in the second volume 230b.

[0039] The housing system 220, 320 also includes a control unit 50 which is connected to the pressure sensors 244a-b and arranged to receive the values ​​of the pressures measured by the pressure sensors 244a-b.

[0040] The control unit 50 is also connected to the upstream 122a and downstream 112b solenoid valves and the opening and closing controls.

[0041] The control unit 50 regularly receives the values ​​transmitted by the pressure sensors 244a-b and representative of the pressures in the volumes 230a-b.

[0042] The control unit 50 compares two successive values ​​of the pressure in each volume 230a-b.

[0043] The control unit 50 is arranged to detect whether the difference in absolute value between two successive values ​​of the pressure in the first volume 230a is less than a first threshold (positive case), i.e. whether the pressure in said first volume 230a remains stable, or whether the difference in absolute value between the two successive values ​​is greater than a second threshold (negative case), i.e. whether the pressure in said first volume 230a varies. The second threshold is greater than or equal to the first threshold.

[0044] In the same way, the control unit 50 is arranged to detect whether the difference in absolute value between two successive values ​​of the pressure in the second volume 230b is less than another first threshold (positive case), that is to say if the pressure in said second volume 230b remains stable, or whether the difference in absolute value between the two successive values ​​is greater than another second threshold (negative case), that is to say if the pressure in said second volume 230b varies. Said other second threshold is greater than or equal to said other first threshold.

[0045] The first threshold and the second threshold, as well as said other first threshold and said other second threshold may be equal at least for some of them or all different. When the control unit 50 detects at least one negative case for the first volume 230a or the second volume 230b, that is to say a difference in absolute value between two successive pressure values ​​beyond the second threshold in the first volume 230a or said other second threshold in the second volume 230b, the control unit 50 commands the closing of the upstream 122a and downstream 112b solenoid valves to isolate the leak.

[0046] When the pressure variation remains below a first threshold for the first volume 230a and the second volume 230b, i.e. two positive cases, the control unit 50 keeps the upstream 122a and downstream 112b solenoid valves open.

[0047] Thus, in the event of detection of a leak of dihydrogen at the level of the pipes and connections, or of a leak in the sealing of the housing 222, the control unit 50 commands the closing of the solenoid valves 122a-b and the housing 222 is then isolated by stopping the flow of dihydrogen and it can be replaced, emptied and repaired during subsequent maintenance operations.

[0048] In the event of a leak in the first volume 230a and to limit the risks of explosion of the housing 222, the housing 222 comprises at a wall of said first volume 230a, here a side wall 224, a pressure relief valve 252 which opens either directly into the open air or into a pipe 254 which channels the escaping gas to a location provided for this purpose. The relief valve 252 is calibrated so as to prevent the pressure from exceeding the resistance of the housing 222.

[0049] To supply the second volume 230b with inert gas, the housing 222 comprises at a wall of said second volume 230b, here a side wall 224, an inlet 256 to which a source of inert gas under pressure is fluidically connected.

[0050] To drain the second volume 230b, the housing 222 comprises at a wall of said second volume 230b, here a side wall 224, an outlet 258 through which the gas contained in the second volume 230b can be evacuated.

[0051] To limit the risk of hydrogen leaks along the pipe 116, it is preferably a double-walled pipe. However, for the parts of the pipe 116 which are located in the housing 222, it is possible to use single-walled pipes for manufacturing simplification.

[0052] In the first embodiment of the invention, the separating wall 234 comprises a rim 260 secured to the walls of the housing 222, here the side walls 224, and extending inside the first volume 230a.

[0053] The separating wall 234 also comprises a central wall 262 extending around the heat exchanger 232 and secured to the latter. The central wall 262 is here parallel to the rim 260.

[0054] The separating wall 234 also comprises a joining wall 264 which extends between the rim 260 and the central wall 262, which is fixed, on the one hand, bearing against a face of the rim 260 facing the second volume 230b and, on the other hand, bearing against a face of the central wall 262 facing the second volume 230b. The joining wall 264 is thus arranged on the side of the second volume 230b relative to the rim 260 and to the central wall 262. The fixing is carried out for example using clamping screws or welding points or any other suitable fixing means. The joining wall 264 is here parallel to the rim 260 and to the central wall 262.

[0055] The position of the junction wall 264 on the side of the second volume 230b prevents the fixing means from working by tearing and makes it possible to press the junction wall 264 against the rim 260 and the central wall 262 due to the pressure difference between the two volumes 230a-b.

[0056] Seals may be arranged between the rim 260 and the joining wall 264, on the one hand, and between the central wall 262 and the joining wall 264, on the other hand.

[0057] In the second embodiment of the invention, the separating wall 334 comprises a rim 360 secured to the walls of the housing 222, here the side walls 224, and extending inside the first volume 230a.

[0058] The separating wall 234 also comprises a central wall 362 extending around the heat exchanger 232 and secured to the latter. The central wall 362 is here parallel to the rim 260. The central wall 362 is fixed in abutment against a face of the rim 360 oriented towards the second volume 230b. The central wall 362 is thus arranged on the side of the second volume 230b relative to the rim 360. The fixing is carried out for example using clamping screws or welding points or any other suitable fixing means.

[0059] The position of the central wall 362 on the side of the second volume 230b prevents the fixing means from working by tearing and allows the central wall 362 to be pressed against the rim 360 due to the pressure difference between the two volumes 230a-b.

[0060] Seals may be arranged between the rim 360 and the central wall 362. According to a particular embodiment, in addition to the pressure sensors 244a-b, the housing system 220, 230 comprises, in each volume 230a-b, at least one additional sensor 274ab-b, among a dihydrogen sensor and a dioxygen sensor. Each additional sensor 274a-b is connected to the control unit 50 which receives additional values ​​of the pressures measured by each additional sensor 274a-b, to compare each additional value thus received with an additional threshold, and to close the solenoid valves 122a-b if an additional value is greater than said additional threshold. The values ​​of the thresholds in each volume 230a-b may be different.According to a particular embodiment, the inner faces of the walls 224 and 226 delimiting the first volume 230a are covered with a protection 270 against thermal radiation such as for example a multi-layer thermal insulator. This protection 270 limits the heating inside the first volume 230a due to an external heat source and thus avoids an increase in pressure in the event of a leak.

[0061] According to a particular embodiment, the outer faces of the walls 224, 226 and 228 of the housing 222 are covered with thermal protection 272. This thermal protection 272 limits the heating inside the housing 222 due to an external heat source and thus prevents an increase in pressure in the event of a leak.

[0062] According to a particular embodiment of the first embodiment, a plate 276 is fixed between the rim 260 and the central wall 262 on the side opposite the junction wall 264. Symmetrically with respect to the junction wall 264, the plate 276 is fixed, on the one hand, bearing against a face of the rim 260 oriented towards the first volume 230a and, on the other hand, bearing against a face of the central wall 262 oriented towards the first volume 230a.

[0063] The plate 276 comprises an insulating layer 278 which bears against the rim 260 and the central wall 262. Such an arrangement contains a possible overpressure in the first volume 230a in the event of a leak and avoids contamination of the second volume 230b and a sudden increase in pressure if the dihydrogen passes from the first volume 230a to the second volume 230b, that is to say from a cold zone to a hot zone.

[0064] In the same way, according to a particular embodiment of the second embodiment, a plate 376 extends around the heat exchanger 232 and is integral with the latter and it is fixed in abutment against the rim 360 on the side opposite the central wall 362, that is to say in the first volume 230a.

[0065] The plate 376 comprises an insulating layer 378 which bears against the rim 360. Such an arrangement contains a possible overpressure in the first volume 230a in the event of a leak and avoids contamination of the second volume 230b and a sudden increase in pressure if the dihydrogen passes from the first volume 230a to the second volume 230b, i.e. from a cold zone to a hot zone.

[0066] According to one embodiment, the control unit 50 comprises, connected by a communication bus: a processor or CPU (“Central Processing Unit” in English); a RAM (“Random Access Memory” in English); a ROM (“Read Only Memory” in English); a storage unit such as a hard disk or a storage media reader such as an SD (“Secure Digital” in English) card reader; at least one communication interface, allowing for example the control unit to communicate with the solenoid valves, the pumps, the pressure sensors, etc.

[0067] The processor is capable of executing instructions loaded into RAM from ROM, external memory (not shown), storage media (such as an SD card), or a communications network. When the equipment is powered on, the processor is capable of reading instructions from RAM and executing them. These instructions form a computer program causing the processor to implement some or all of the algorithms and steps described above.

[0068] All or part of the algorithms and steps described below can be implemented in software form by executing a set of instructions by a programmable machine, for example a DSP (“Digital Signal Processor”) or a microcontroller, or be implemented in hardware form by a machine or a dedicated component, for example an FPGA (“Field-Programmable Gate Array”) or an ASIC (“Application-Specific Integrated Circuit”).

Claims

1. Casing system (120, 220, 320) which is intended to be mounted between a supply pipe (240) and a discharge pipe (242) in which a heat exchange fluid circulates, the casing system (120, 220, 320) comprising: - a sealed casing (222) which is divided by a sealed separation wall (234, 334) into a first volume (230a) and a second volume (230b) which is filled with a gas which is inert with respect to dihydrogen, - a vacuum pump (250) which is connected in fluid terms to the first volume (230a) and which is configured, during operation, to generate the make vacuum in the first volume (230a), - an upstream pipe (116a) along which an upstream solenoid valve (122a) is mounted and which is intended to be connected in fluid terms to a dihydrogen tank (110), - a downstream pipe (116b) along which a downstream solenoid valve (122b) is mounted and which is intended to be connected in fluid terms to an engine (106), - a heat exchanger (232) which is fixed inside the casing (222) through the separation wall (234, 334) and which has a first inlet (236a) which is connected in fluid terms to the upstream pipe (116a) downstream of the upstream solenoid valve (122a) and a first outlet (238a) which is connected in fluid terms to the downstream pipe (116b) upstream of the downstream solenoid valve (122b) and which has a second inlet (236b) which is intended to be connected in fluid terms to the supply pipe (240) and a second outlet (238b) which is intended to be connected in fluid terms to the discharge pipe (242), wherein the first inlet (236a) is arranged in the first volume (230a) and the first outlet (238a) is arranged in the second volume (230b), - a first pressure sensor (244a) which is arranged in the first volume (230a), - a second pressure sensor (244b) which is arranged in the second volume (230b), - a control unit (50) which is arranged to receive pressure values measured by the pressure sensors (224a-b) in order to detect, on the one hand, if the deviation in absolute value between two successive values of the pressure in the first volume (230a) is less than a first threshold or greater than a second threshold which is greater than or equal to the first threshold and, on the other hand, if the deviation in absolute value between two successive values of the pressure in the second volume (230b) is less than another first threshold or greater than another second threshold which is greater than or equal to the other first threshold, and to close the solenoid valves (122a-b) if it detects a deviation in absolute value between two successive pressure values beyond the second threshold in the first volume (230a) or the other second threshold in the second volume (230b).

2. Casing system (120, 220, 320) according to claim 1, characterised in that the casing (222) comprises in the region of a wall of the first volume (230a) a pressure relief valve (252).

3. Casing system (120, 220, 320) according to either claim 1 or 2, characterised in that the casing (222) comprises, in the region of a wall of the second volume (230b), an intake (256) which is intended to be connected in fluid terms to a source of inert gas under pressure.

4. Casing system (120, 220, 320) according to any one of claims 1 to 3, characterised in that the casing (222) comprises, in the region of a wall of the second volume (230b), a discharge (258) via which the gas can be discharged.

5. Casing system (220) according to any one of claims 1 to 4, characterised in that the separation wall (234) comprises an edge (260) which is fixedly joined to the walls of the casing (222) and which extends inside the first volume (230a), a central wall (262) which extends around the heat exchanger (232) and which is fixedly joined thereto, and a connection wall (264) which extends between the edge (260) and the central wall (262) and which is fixed in abutment against a face of the edge (260) which is orientated towards the second volume (230b) and in abutment against a face of the central wall (262) which is orientated towards the second volume (230b).

6. Casing system (320) according to any one of claims 1 to 4, characterised in that the separation wall (334) comprises an edge (360) which is fixedly joined to the walls of the casing (222) and which extends inside the first volume (230a) and a central wall (362) which extends around the heat exchanger (232) and which is fixedly joined thereto, wherein the central wall (362) is fixed in abutment against a face of the edge (360) which is orientated towards the second volume (230b).

7. Casing system (120, 220, 320) according to any one of claims 1 to 6, characterised in that it comprises for each volume (230a-b) at least one additional sensor (274a-b), from a dihydrogen sensor and a dioxygen sensor, which is arranged in the volume (230a-b), in that the control unit (50) is arranged to receive additional values of the pressures measured by each additional sensor (274a-b) in order to compare each additional value received in this manner with an additional threshold and to close the solenoid valves (122a-b) if an additional value is greater than the additional threshold.

8. Aircraft (100) comprising: - a dihydrogen tank (110), - an engine (106), - a casing system (120, 220, 320) according to any one of the preceding claims, wherein the upstream pipe (116a) extends between the tank (110) and the first inlet (236a) of the heat exchanger (232), wherein the downstream pipe (116b) extends between the first outlet (238a) of the heat exchanger (232) and the engine (106), and, - a heat exchange fluid circuit which comprises a supply pipe (240) which is connected in fluid terms to the second inlet (236b) of the heat exchanger (232) and a discharge pipe (242) which is connected in fluid terms to the second outlet (238b) of the heat exchanger (232).