Thermal protection structure

0001The present invention relates to thermal protection structures.

0002Although not exclusively, such protection structure heat is more particularly suitable for construction elements to be subjected to very high temperatures, and in particular the construction of combustion chambers, including ramjet, or external thermal protection plates flying gear high speeds, for example beyond Mach Mach 10 or 12.

0003To be used in the above applications, such structure must have certain characteristics, including:<ul><li>a mass and a reduced thickness; and</li><li>if it uses a cooling fluid, a hydraulic resistance the as low as possible and reduced use of this fluid.</li></ul>

0004different solutions are known to carry a structure thermal protection for such applications.

0005A first known solution is to use ablative material, whose thin surface layers are ablated during its use as protective structure. However, this solution usual presents the following drawbacks:<ul><li>the material surface and thus the shape of the structure are modified during use, which can be annoying, particularly when the form affects the operation of the machine or device provided with said structure;</li><li>this structure is not reusable; and especially</li><li>high thickness of ablative material is necessary, which implies a large mass.</li></ul>

0006A second known solution is to use the means of cooling by convection. These means comprise a cooling fluid, for example hydrogen, which circulates in a duct.

0007A wall of said conduit which is in contact with the environment hot outer is made of a good heat conducting material and thin so as to cause the heat to said coolant which is continuously regenerated. Such implementation requires therefore a large amount of fluid and a high throughput. For this purpose, generally increases the pressure of said fluid, which requires strengthen the walls of the duct thus causing an increase in cost, thickness and / or mass. In addition, because a significant difference of linear expansion between said thermally conductive wall and the rest of the structure, there are risks of cracking and, consequently, destruction of said structure.

0008A third known solution consists in using means cooling by ejection, which comprise a porous wall permeable fluid and a cooling fluid which is ejected through said porous wall, in the hot external environment. This allows ejection created outside the structure of a boundary layer temperature of gas reduced, allowing to thermally protect said structure. However, This solution is generally effective only locally. Of Furthermore, the ejected cooling fluid is of course lost, which is annoying when said fluid is present in reduced amount or, especially, when said fluid is the fuel, for example hydrogen, a flying machine provided with said structure, which can lead a limitation or a fall of the thrust of said flying object.

0009In addition, a fourth solution is known to thermally protect an element using a thermal barrier. This solution which is a passive protection uses a waterproof material thermally insulating. However, this solution is not generally effective for a limited period.

0010Furthermore, in addition to the disadvantages already mentioned, no the above solutions is able to protect effectively and sufficiently a combustion chamber of a ramjet for flights beyond Mach 12.

0011The present invention aims to remedy these drawbacks. It concerns different thermal protection structures, simple and inexpensive design, and above all extremely effective, can be used in a combustion chamber or reactor high temperatures, particularly in a combustion chamber a ramjet at high flight speeds, or as thermal protection external surfaces of aircraft and spacecraft.

0012To this end, according to the invention, a first protection structure heat is remarkable in that it comprises:<ul><li>ejection by cooling means, which eject a first cooling fluid outside said structure; and</li><li>a thermal barrier forming at least a portion of the outer wall of said structure, said thermal barrier being perforated so to permit ejection of said first cooling fluid.</li></ul>

0013Thus, thanks to the combined use of said cooling means by ejection and said thermal barrier to create a combined protective effect, thermal protection is obtained specifically effective.

0014Note that the thermal barrier, which is usually carried out impermeable way, is perforated in the structure according to the invention. Although such use goes against the prior art, the thermal protection effect obtained by this thermal barrier is not reduced, because of its combination with said cooling means by ejection that ejects a cold fluid through the holes said thermal barrier and thus prevent the passage of heat through these holes.

0015Furthermore, a second thermal protection structure is remarkable, according to the invention in that it comprises:<ul><li>ejection by cooling means, which eject a first cooling fluid outside said structure; and</li><li>means for cooling by convection, which comprise a second cooling fluid circulating in said structure, said first and second cooling fluids being from the same fluid.</li></ul>

0016Thus, thanks to the combined use of said cooling means by ejection and by convection, resulting in a protective effect combined heat, thermal protection is obtained specifically effective.

0017The fluid flow is thus divided into longitudinal flow said second cooling fluid (in said structure) and a transverse flow of said first cooling fluid (outside said structural.

0018Through the use of a single fluid:<ul><li>simplifies said structure;</li><li>is allowed by a single pressure control and / or adjust flow the two parts of fluid, as discussed below; and</li><li>one can optimize the flow of said fluid.</li></ul>

0019In addition, a third thermal protection structure is remarkable, according to the invention in that it comprises:<ul><li>a thermal barrier forming at least a portion of the outer wall of said structure; and</li><li>means for cooling by convection, which comprise a second cooling fluid which circulates inside of the structure with respect to said thermal barrier.</li></ul>

0020Thus, through this combined use of said thermal barrier and said convection cooling means, resulting in a conjugate heat protection effect is also obtained a protection efficient heat.

0021Note again that it is against the state of the art which teaches that the cooling means by convection must comprise a highly thermally conductive outer wall. Gold, in said structure, said outer wall is formed by the barrier heat which produces a lowering of the temperature.

0022Therefore, the extra temperature drop before be produced by said means for cooling by convection is scaled down. This allows in particular to be less demanding as regards the properties and efficacy of said cooling means, and in particular coolant used.

0023In addition, in a preferred embodiment of the invention said thermal protection structure has three elements simultaneously cited above, namely the ejection by cooling means, the cooling means by convection and the thermal barrier, provides simultaneously all the effects and all the above benefits. In addition, this embodiment optimizes the said elements, in particular by minimizing the flow of fluid and the mass the walls of the structure, while ensuring mechanical integrity and the required and thermal thereof.

0024Moreover, advantageously, the structure according to the invention comprises: <ul><li>at least one conduit in which the fluid circulates comprising at least one of said first and second cooling fluids; and</li><li>means for adjusting the pressure of said fluid inside said conduit, said generating means preferably a pressure which is function of the pressure prevailing outside said structure, example a pressure which is greater than or equal to twice the pressure maximum external.</li></ul>

0025Furthermore, advantageously, said cooling means by convection comprise a thermally conductive son network, said network being permeable to said fluid and arranged preferably in said leads into contact with at least one of its walls. This optimizes the heat exchange between the cooling fluid and the wall or walls (Hot) of said cooling means.

0026In order to optimize fluid flow, advantageously:<ul><li>said thermal barrier is perforated so as to have a resistance hydraulic which is a function of the flow resistance within said conduit. Preferably, the hydraulic resistance of said thermal barrier is less than or equal to one tenth of the resistance hydraulic internal to said conduit; and or</li><li>the structure further comprises means for adjusting the flow of said fluid in said conduit.</li></ul>

0027The figures of the appended drawing will elucidate the invention may be embodied. In these figures, identical references denote similar elements.

0028Figure 1 illustrates schematically and partially a structure according to the invention and further shows a diagram illustrating the pressure outside of said structure.

0029Figure 2 is a schematic section on the line II-II of Figure 1.

0030The structure 1 according to the invention and shown schematically Figures 1 and 2 is a thermal protection structure capable of providing protection against high temperatures.

0031It may in particular be used in a combustion chamber or a reactor at high temperatures, in particular in a chamber combustion of a ramjet at high flight speeds (for achieve such a hypersonic long-term), or as protection heat external surfaces of aircraft and spacecraft.

0032In the example shown, said structure 1 is constructed as form of a generally planar panel. Of course, within the framework of the present invention, the heat insulation structure can also have a different shape, such as a curved shape. said structure according to the invention can in particular be used as the leading edge, in particular a drift or a propeller.

0033According to the invention, said structure 1 comprises:<ul><li>a thermal barrier 2 of a known type, forming the outer wall subjected to an elevated temperature of said structure 1. Said barrier thermal 2 is provided with through holes 3;</li><li>4A ejection means of cooling, which eject a first cooling fluid outside said structure 1, through said through holes 3 of the thermal barrier 2 as shown by arrows 5A. This fluid ejected form the usual way, a layer temperature limit reduced on the outer face 6 of the barrier thermal 2; and</li><li>4B of the cooling means by convection, which comprise a second cooling fluid which circulates in said structure 1, as shown by arrows 5B, and in particular in a conduit 7 in the form of a parallelepiped chamber, the outer wall is formed by the thermal barrier 2 and which has a wall internal 8.</li></ul>

0034According to the invention, said first and second fluids to flow transverse and longitudinal respectively, illustrated by arrows 5A and 5B, are from the same fluid, the flow of which is represented by arrows 5. Also, said means 4A and 4B comprise a single same circuit 9 fluid supply, described below.

0035Thus, thanks to the invention, thermal protection is obtained particularly effective, especially due to the combined effects of the elements thermal protection 2, 4A and 4B combined. The structure 1 can perfectly fulfill all the requirements in the above applications.

0036Moreover, thanks to the above combination according to the invention said elements 2, 4A and 4B, said structure 1 is particularly embodiment simple, compact and inexpensive.

0037In addition, according to the invention, said circuit 9 fluid supply which opens into the conduit 7 through openings 10 and 11 comprises:<ul><li>means 12, of known type, for adjusting the pressure of the fluid in said circuit 9, and in particular in the duct 8; and</li><li>means 13, of known type, to control the flow of said fluid in said circuit 9, and therefore also in said conduit 7.</li></ul>

0038In FIG 1 there is further shown a graph showing a curve C illustrating the existing pressure P on the outer face 6 of the 1 structure along the longitudinal direction XX.

0039According to the invention, the means 12 regulate pressure so as to generating in the conduit 7 a pressure which is a function of the pressure P existing outside said structure 1.

0040In a particular embodiment, they generate pressure which is greater than or equal to twice the maximum external pressure PO.

0041Such pressure difference allows a supercritical ejection or at least critical, said first outside coolant of the structure 1.

0042Therefore, when the hot external environment includes a hot fluid flow, for example in the case of an engine, Such ejection prevents contact between the hot fluid and the outer face 6 of the structure 1, which enables to protect mechanically.

0043Said means 4B further includes a network 14 to three dimensions, formed from a metal screen structure of son 15 good drivers thermal. Said network 14 is arranged in said conduit 7 contacting its walls 2 and 8 and increases the heat exchange between the cooling fluid (arrow 5B) and said walls 2 and 8. Moreover, said network 14 is highly permeable, so that it has only a reduced hydraulic resistance to flow of said fluid (arrow 5B).

0044This reduces the thickness of the wall 8 and the mass said means 4b.

0045According to the invention, the holes 3 (including their number, size and distribution) and said grid 14 are adapted each other so as obtain a determined relationship to their respective hydraulic resistance. Preferably, seeking hydraulic resistance the thermal barrier 2 which is less than or equal to one tenth of the resistance said hydraulic network 14.

0046This allows to precisely adjust the proportions between the amount of ejected fluid (arrows 5A) and the amount of fluid recirculated (Arrows 5B) and for cooling by convection.

0047Note that most of the operational efficiency of the structure 1 is in particular determined by the following two parameters, which are adjustable according to the invention:<ul><li>fluid flow; and</li><li>the ratio of the amount of ejected fluid and the amount of fluid used for convection,</li></ul>these two parameters being set to reduced values ​​for carrying practice of the present invention.

0048Furthermore, in the case where the structure 1 is arranged on a vehicle steering wheel not shown, burning a fuel, for example hydrogen, said fuel can be used as a cooling fluid, since the amount of ejected fluid is low and thus the structure 1 according to the invention does not reduce the thrust and performance of said flying craft.