System for heating the cabin of an aircraft provided with an annular heat exchanger around the exhaust nozzle

Abstract

A heating system (50) for heating a cabin (2) of an aircraft (1), said heating system including an annular heat exchanger (10) positioned around an exhaust pipe (21) of a turbine engine (20), and through which a heat transfer fluid (14) and ambient air (25) flow. Said heat exchanger (10) is provided with a rear casing situated at an outlet of said heat exchanger (10) and directing the ambient air (25) exiting form said heat exchanger (10) towards said exhaust gas (15) exiting via said exhaust pipe (21). Said exhaust gas (15) then generates a flow of ambient air (25) through said heat exchanger (10) by the Coanda effect. Said ambient air (25) flowing through said heat exchanger (10) is thus heated by convection from said pipe (21), and said heat transfer fluid (14) is heated firstly by radiation from said pipe (21) and secondly by convection between said heat transfer fluid (14) and said ambient air (25).

Claims

1. A heat exchange arrangement comprising an annular heat exchanger and a pipe, said heat exchanger, through which a first fluid flows, being positioned around said pipe, through which a second fluid flows, said second fluid exiting from said pipe via an opening in said pipe, and a third fluid flowing through said heat exchanger from an inlet of said heat exchanger to an outlet of said heat exchanger; wherein said heat exchanger further comprises a rear casing situated at said outlet and directing said third fluid towards said second fluid exiting via said opening, the second fluid then generating a flow of said third fluid through said heat exchanger by a Coanda effect, heat exchange taking place between said pipe, said third fluid, and said first fluid.

2. A heat exchange arrangement according to claim 1, wherein said heat exchange is constituted at least by heat exchange by convection between said pipe and said third fluid.

3. A heat exchange arrangement according to claim 1, wherein said heat exchange is constituted at least by heat exchange by radiation between said pipe and said first fluid.

4. A heat exchange arrangement according to claim 1, wherein said heat exchange is constituted at least by heat exchange by convection between said third fluid and said first fluid.

5. A heat exchange arrangement according to claim 1, wherein said heat exchanger further comprises a thermal protection positioned at least partially between said pipe and said heat exchanger in order to limit said heat exchange with said pipe.

6. A heat exchange arrangement according to claim 5, wherein said thermal protection is constituted by at least one heat screen formed of one or more elements chosen from a list comprising a material of a metal foam type, concentric cylindrical plates, and a honeycomb structure.

7. A heat exchange arrangement according to claim 5, wherein said thermal protection has thermal effectiveness that increases going from said inlet towards said outlet, said heat exchange being essentially obtained firstly by radiation between said pipe and said first fluid, and secondly by convection between said pipe and said third fluid in an inlet zone of said heat exchanger while, beyond said inlet zone, said heat exchange is obtained by radiation between said pipe and said first fluid, by convection between said pipe and said third fluid, and by convection between said third fluid and said first fluid, said inlet zone being formed by a zone situated inside said heat exchanger immediately after said inlet in a direction of flow of said third fluid through said heat exchanger.

8. A heat exchange arrangement according to claim 1, wherein, with said heat exchanger being provided with a front casing in an inlet zone of said heat exchanger, the heat exchange in said inlet zone is obtained only by convection between said pipe and said third fluid, said inlet zone being formed by a zone situated inside said heat exchanger immediately after said inlet in the direction in which said third fluid flows through said heat exchanger, said first fluid not flowing through said inlet zone.

9. A heat exchange arrangement according to claim 8, wherein, with said heat exchanger being provided with a thermal protection positioned at least partially between said pipe and said heat exchanger, said thermal protection has thermal effectiveness that starts beyond said inlet zone and decreases going to said outlet, said heat exchange being obtained only by convection between said pipe and said third fluid in said inlet zone, and then beyond said inlet zone said heat exchange being obtained by radiation between said pipe and said first fluid, by convection between said pipe and said third fluid, and by convection between said third fluid and said first fluid.

10. A heat exchange arrangement according to claim 1, wherein said rear casing has a convergent shape that is in contact with a peripheral portion of the flow of said second fluid exiting from the outlet of said pipe, and that extends beyond said pipe in order to bring said third fluid into contact with said second fluid.

11. A heat exchange arrangement according to claim 1, wherein said third fluid is ambient air.

12. A heat exchange arrangement according to claim 1, wherein said pipe is an exhaust pipe for discharging exhaust gas from an engine, and said second fluid is formed by said exhaust gas.

13. A heating system for heating a vehicle, said vehicle being provided with a cabin and with at least one engine, said heating system including at least one set of piping through which a heat transfer fluid circulates, circulator means for circulating said heat transfer fluid, and at least one heater element though which said heat transfer fluid circulates in order to heat said cabin, wherein said heating system includes a heat exchange arrangement according to claim 12, making it possible to heat said heat transfer fluid, said heat transfer fluid being said first fluid of said heat exchanger.

14. A heating system according to claim 13, wherein said vehicle is a rotary-wing aircraft, said engine is a turbine engine, and said pipe is constituted by at least one exhaust nozzle of at least one turbine engine.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail from the following description of embodiments given by way of illustration with reference to the accompanying figures, in which:

(2) FIG. 1 shows a rotary-wing aircraft equipped with a heating system for heating its cabin;

(3) FIG. 2 shows a first embodiment of a heat exchange arrangement equipping said heating system; and

(4) FIG. 3 shows a second embodiment of a heat exchange arrangement equipping said heating system.

(5) Elements present in more than one of the figures are given the same references in each of them.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows a rotary-wing aircraft 1 provided, in particular, with a cabin 2, with a turbine engine 20, with an exhaust pipe 21, and with a heating system 50. This heating system 50 includes a first fluid 14 flowing through piping 53, circulation means 51 for causing said first fluid 14 to circulate, a heater element 52, and a heat exchange arrangement 30 provided with an annular heat exchanger 10 and with an exhaust pipe 21. This first fluid 14 is a heat transfer fluid that is heated in the annular heat exchanger 10 and that can thus heat the cabin 2 of the aircraft 1 via the heater element 52.

(7) FIGS. 2 and 3 show two embodiments of this heat exchange arrangement 30.

(8) Regardless of the embodiment, the annular heat exchange element 10 is positioned around the exhaust pipe 21 of the aircraft 1, through which pipe a second fluid 15 formed by the exhaust gas from the turbine engine 20 flows. In general, this exhaust pipe 21 is substantially cylindrical in shape.

(9) The annular heat exchanger 10 has an enclosure 11 connected to the piping 53 and through which the first fluid 14 circulates, and it also has an inlet 12 and an outlet 13, via which inlet and outlet a third fluid 25 enters and exits from this annular heat exchanger 10. Thus, the outside surface of the enclosure 11 constitutes a heat exchange surface for heat exchange between the first fluid 14 and the third fluid 25. Therefore, heat exchange by convection can, inter alia, take place between the first fluid 14 and the third fluid 25. This third fluid 25 is the ambient air surrounding the aircraft 1.

(10) The annular heat exchanger 10 also has a rear casing 17 directing the ambient air 25 exiting via the outlet 13 of the heat exchanger 10 towards the exhaust gas 15 exiting from the opening 23 in the pipe 21. The shape of this rear casing 17 enables the exhaust gas 15 to generate the phenomenon whereby ambient air 25 is entrained by the Coanda effect. Ambient air 25 is entrained at the outlet 13 of the heat exchanger 10 by the flow of the exhaust gas 15 exiting from the pipe 21, generating lower pressure inside the heat exchanger 10, thereby causing ambient air 25 to be sucked in at the inlet 12 of the heat exchanger 10. Thus, the ambient air 25 is caused to flow through the heat exchanger 10.

(11) The rear casing 17 must be in contact with a peripheral portion of the flow of the exhaust gas 15 exiting from the pipe 21, as shown in FIGS. 2 and 3. Said rear casing 17 then extends beyond the opening 23 in the pipe 21 in order to direct the ambient air 25 accurately towards the exhaust gas 15. The rear casing 17 has a convergent shape so as to bring the ambient air 25 into contact with the exhaust gas 15. A mixing zone A in which the ambient air 25 and the exhaust gas 15 mix then appears.

(12) In addition, the exhaust gas 15 flowing through the pipe 21 is very hot, and of the order of 700 C., and it exits from the pipe 21 via the opening 23. The pipe 21 is also hot. Therefore, heat exchange can take place firstly by radiation between the pipe 21 and the first fluid 14 via the heat exchange surface of the enclosure 11, and secondly by convection between the pipe 21 and the third fluid 25.

(13) However, the annular heat exchanger 10 equips a heating system 50, and the first fluid 14 feeds a heater element 52. The temperature of said first fluid 14 must therefore not be excessive, firstly so as not to overheat the cabin 2 of the aircraft 1 and secondly so that the temperature of the piping 53 through which the first fluid 14 circulates is not excessive. For this purpose, the annular heat exchanger 10 has a thermal protection positioned at least partially between the pipe 21 and the annular heat exchanger 10. The amount of heat exchanged with the pipe 21, be it by radiation or by convection, can thus be limited. Said thermal protection comprises at least one heat screen 19 and it may be constituted by a material of the metal foam type, e.g. steel or copper foam, or by concentric cylindrical plates or else by a honeycomb structure, which plates or structure are, for example, made of stainless steel, of titanium, or of graphite materials.

(14) In addition, the annular heat exchanger 10 has three zones 31, 32, 33. An inlet zone 31 is situated immediately after the inlet 12 of the heat exchanger 10 in the direction of flow of the ambient air 25 through the exchanger 10, and an outlet zone 33 is situated immediately before the outlet 13 of the heat exchanger 10. A central zone 32 is situated between the inlet zone 31 and the outlet zone 33.

(15) In a first embodiment of the heat exchange arrangement 30 shown in FIG. 2, the thermal protection of the annular heat exchanger 10 is formed by three heat screens 19a, 19b, 19c. A first heat screen 19a covers all three zones 31, 32, 33, while a second heat screen 19b covers only the central zone 32 and the outlet zone 33. A third heat screen 19c covers only the outlet zone 33. These three heat screens 19a, 19b, 19c have the same thermal effectiveness by, for example, being made of the same material and having the same thickness. In addition, the enclosure 11 inside which the first fluid 14 circulates is situated in all three zones 31, 32, 33. This enclosure 11 is of tubular shape and is constituted by one or more tubes snaking through the annular heat exchanger 10.

(16) Thus, in the inlet zone 31, the heat exchanger 10 has a single heat screen 19a. Therefore, the amount of heat exchanged with the pipe 21 is large, making it possible firstly, by radiation, to heat the first fluid 14 circulating inside the enclosure 11, and secondly, by convection, to heat the ambient air 25 flowing through the heat exchanger 10. However, the ambient air 25 that has just entered the heat exchanger 10 has a temperature close to the temperature outside the aircraft 1 and therefore does not heat the first fluid 14 by convection.

(17) Then, in the central zone 32, the heat exchanger 10 has two heat screens 19a, 19b. Therefore, the amount of heat exchanged with the pipe 21 is lower than in the inlet zone 31. However, it makes it possible to heat the first fluid 14 by radiation and to heat the ambient air 25 flowing through the heat exchanger 10 by convection. In addition, since the ambient air 25 has been heated by radiation in the inlet zone 31, it can heat the first fluid 14 by convection.

(18) Finally, in the outlet zone 33, the heat exchanger 10 has three heat screens 19a, 19b, 19c. As a result, the amount of heat exchanged with the pipe 21 is further reduced relative to the amount of heat exchanged in the inlet zone 31 and in the central zone 32. However, it can heat the first fluid 14 slightly, by radiation, and it can heat the ambient air 25 flowing through the heat exchanger 10 slightly, by convection, the first fluid 14 essentially being heated by convection from the ambient air 25.

(19) Thus, the thermal protection of the annular heat exchanger 10 in this first embodiment has thermal effectiveness that increases going from the inlet 12 of the heat exchanger 10 towards its outlet 13.

(20) In a second embodiment of the heat exchange arrangement 30 shown in FIG. 3, no protection is present in the inlet zone 31, while the thermal protection of the annular heat exchanger 10 is formed by a single heat screen 19 in the central zone 32 and in the outlet zone 33. In addition, the thickness of said heat screen 19 decreases going from the central zone 32 towards the outlet zone 33, the enclosure 11 inside which the first fluid 14 circulates being situated only in the central zone 32 and in the outlet zone 33. This enclosure 11 is constituted by one or more sets of superposed plates. In addition, a front casing 18 forms the inlet 12 of the heat exchanger 10 and said inlet zone 31.

(21) Thus, in the inlet zone 31, only ambient air 25 flows. Heat exchange takes place by convection between the pipe 21 and the ambient air 25. In addition, this heat exchange by convection is at its maximum since no thermal protection is present in this inlet zone 31.

(22) Then, in the central zone 32, the first fluid 14 circulates inside the enclosure 11 and the ambient air 25 heated in the inlet zone 32 flows through the heat exchanger 10. As a result, the heat exchange is essentially obtained by convection between the ambient air 25 heated in the inlet zone 31 and the first fluid 14, the majority of the heat exchanged with the pipe 21 being stopped by the heat screen 19 which is of large thickness in the central zone 32. However, heat exchange nevertheless takes place firstly by radiation between the pipe 21 and the first fluid 14, and secondly by convection between the pipe 21 and the ambient air 25.

(23) Finally, in the outlet zone 33, the heat exchange by convection between the ambient air 25 and the first fluid 14 decreases. The heat taken up by and stored in the ambient air 25 in the inlet zone 31 has, to a large extent, been transmitted to the first fluid 14 in the central zone 32. However, since the thickness of the heat screen 19 is smaller in this outlet zone 33, the amount of heat exchanged with the pipe 21 increases considerably. Thus, in this outlet zone 33, a majority of the heat exchange takes place with the pipe 21, making it possible firstly to heat the first fluid 14 by radiation and secondly to heat the ambient air 25 by convection, and also, a minority of the heat exchange takes place by convection between the ambient air 25 and the first fluid 14.

(24) In addition, regardless of the embodiment of the heat exchange arrangement 30 of the invention, the thermal protection limiting the heat exchange of the pipe 21 in the heat exchanger 10 makes it possible to limit the temperature of the first fluid 14 to a temperature of in the range 80 C. to 100 C. while said first fluid is circulating through the piping 53 during heating of the cabin 2 of the aircraft 1, the internal portion of said heat exchanger 10 having a temperature of approximately in the range 100 C. to 120 C.

(25) Conversely, when there is no need to heat the cabin 2 of the aircraft 1, the circulation of the first fluid 14 can be stopped, or else its flow rate can be reduced, and the temperature of the internal portion of the heat exchanger 10 is then limited, for example, to about 250 C., by means of the presence of the thermal protection. The temperature of the first fluid 14 can then be greater than its operating temperature which lies approximately in the range 80 C. to 100 C. as mentioned above, without going beyond the maximum temperature acceptable for said first fluid 14.

(26) Naturally, the present invention is capable of numerous variations concerning its implementation. Although several embodiments are described, it should readily be understood that it is not conceivable to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention. In particular, the number of heat screens 19 present in the two embodiments that are described is non-limiting, it being possible for said number of heat screens 19 to be different depending on the embodiment of the invention.