Sweat cooling composite thermal protection structure based on porous metamaterial

Abstract

The invention discloses a sweating and cooling composite thermal protection structure based on a porous metamaterial, which belongs to the technical field of active thermal protection of aircrafts and comprises a layered metamaterial composite structure body. The layered metamaterial composite structure body sequentially comprises a spectrum stealth porous superstructure layer, an infrared thermal stealth porous superstructure layer and a hydrogel filling layer from top to bottom. The infrared thermal stealth superstructure porous material is used as a core, the anisotropic thermal conductivity characteristic of the infrared thermal stealth porous superstructure layer is achieved through the micro-nano structure design and different porosity distribution, transfer of surface heat flow in the horizontal direction and transfer of heat to the coolant phase change layer in the vertical direction can be accelerated, a sweating cooling mechanism is triggered, and the heat transfer efficiency is improved. Local high temperature of the surface is effectively eliminated, the average temperature of the surface is rapidly reduced, and the heat radiation amount is reduced, so that efficient thermal protection is achieved, the infrared thermal stealth function is achieved, and the spectrum stealth requirement is also met by combining the surface spectrum stealth porous superstructure layer.

Description

Technical Field

[0001] The present invention relates to the technical field of active thermal protection for aircraft, and particularly to a sweating cooling composite thermal protection structure based on porous metamaterials. Background Art

[0002] With the continuous development of aerospace technology, the flight speed of a new generation of aircraft has been significantly improved. However, in the state of high-speed flight, the surface of the aircraft needs to bear huge aerodynamic heat loads. Especially in key parts such as the leading edge of the aircraft and the lip of the intake duct, the aerodynamic force and aerodynamic heat problems are particularly prominent, bringing great hidden dangers to flight safety. Therefore, it is necessary to strengthen the research on the thermal protection system of the aircraft. Sweating cooling is a highly efficient active cooling method. Using porous materials as the matrix, and taking advantage of the huge specific surface area of the porous structure, the cooling working fluid can fully conduct convective heat transfer with the solid; at the same time, after the cooling working fluid flows out, a low-temperature heat-insulating gas film is formed on the outer surface of the porous structure, further protecting the surface structure of the aircraft, and having broad application prospects in the field of aircraft thermal protection.

[0003] During the high-speed flight process, the surface of the aircraft not only faces the challenge of an extreme thermal environment, but also needs to cope with the threats of infrared detection and optical detection. The current stealth technologies mainly include types such as radar stealth, laser stealth, acoustic stealth, and infrared thermal radiation stealth. However, the traditional aircraft thermal protection structure usually only has a single thermal protection function and is difficult to meet the comprehensive requirements of thermal protection, infrared stealth, and spectral stealth at the same time; the existing infrared thermal stealth technologies mainly achieve it by reducing the surface temperature of the target, but it is difficult to take into account the requirements of spectral stealth; while the spectral stealth technology based on the design of metamaterials has the defect of insufficient thermal protection performance. Therefore, it is of great significance to develop an integrated structure that combines the functions of aircraft thermal protection, infrared thermal stealth, and spectral stealth. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems existing in the prior art, and propose a sweating cooling composite thermal protection structure based on porous metamaterials, which realizes the integrated functions of spectral stealth, infrared thermal stealth, and efficient active thermal protection through multi-layer metamaterial design and sweating cooling technology.

[0005] In order to achieve the above purpose, the present invention adopts the following technical scheme: A sweating cooling composite thermal protection structure based on porous metamaterials, including a layered metamaterial composite structure body, and the layered metamaterial composite structure body successively includes the following components from top to bottom: a spectral stealth porous superstructure layer, an infrared thermal stealth porous superstructure layer, and a hydrogel filling layer.

[0006] As a preferred solution, the spectral stealth porous superstructure layer designs the geometric shape and arrangement of micro-nano structure units according to the principle of an optical invisibility cloak and the requirements of the stealth wavelength band by using transformation optics theory; By regulating the geometric shape and arrangement of the micro-nano structure units, spectral stealth in the visible light, infrared, and microwave wavelength bands is achieved.

[0007] As a preferred solution, the material of the spectral stealth porous superstructure layer is a metal material-dielectric composite metamaterial. The metal materials include copper, silver, and aluminum, and the dielectric materials include silicon dioxide, silicon nitride, and aluminum oxide; The preparation method of the spectral stealth porous superstructure layer includes 3D printing technology, electron beam lithography, and nanoimprinting technology; The thickness of the spectral stealth porous superstructure layer is 2-6 mm.

[0008] As a preferred solution, the infrared thermal stealth porous superstructure layer is a double-layer porous structure, including an upper structure with a low porosity and a lower structure with a high porosity. The high porosity of the lower structure provides space for hydrogel filling.

[0009] As a preferred solution, the material of the infrared thermal stealth porous superstructure layer includes ceramic matrix composite materials and high-temperature resistant nickel-based alloy porous materials; The thickness of the infrared thermal stealth porous superstructure layer is 10-20 mm.

[0010] As a preferred solution, the hydrogel filling layer is located within the lower structure of the infrared thermal stealth porous superstructure; The hydrogel filling layer selects a hydrogel material with high heat absorption capacity and phase change characteristics as a solid coolant and fills the pores of the lower structure of the infrared stealth porous superstructure layer.

[0011] As a preferred solution, the hydrogel filling layer uses 50-mesh superabsorbent resin particles and prepares the hydrogel by adding them to deionized water according to a mass ratio of 1:100; The thickness of the hydrogel filling layer is 5-10 mm.

[0012] Compared with the prior art, the beneficial effects of the present invention are: The integrated sweating cooling thermal protection structure for metamaterial optical stealth - infrared stealth innovatively integrates three major functions: infrared spectrum stealth, infrared thermal stealth, and sweating cooling active thermal protection. The integrated sweating cooling thermal protection structure for metamaterial optical stealth - infrared thermal stealth takes the infrared thermal stealth superstructure porous material as the core, and realizes the anisotropic thermal conductivity characteristics of the infrared thermal stealth porous superstructure layer through micro - nano structure design and different porosity distributions. This design can accelerate the transfer of surface heat flux in the horizontal direction and the heat transfer to the coolant phase change layer in the vertical direction, trigger the sweating cooling mechanism, effectively eliminate local high temperatures on the surface, rapidly reduce the surface average temperature, and reduce the amount of thermal radiation, so as to achieve efficient thermal protection while realizing the infrared thermal stealth function. Combining with the surface spectral stealth porous superstructure layer also takes into account the spectral stealth requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. is a three - dimensional structural schematic diagram of a sweating cooling composite thermal protection structure based on porous metamaterials proposed by the present invention; Figure 2 FIG. is a structural schematic diagram of an infrared thermal stealth porous superstructure layer; Figure 3 FIG. is a structural schematic diagram of a second infrared thermal stealth porous superstructure layer; Figure 4 FIG. is a structural schematic diagram of a third infrared thermal stealth porous superstructure layer; Figure 5 FIG. is a comparison of the numerical simulation results of the total thermal radiation on the outer surface of the non - cooling structure, single sweating cooling structure, and metamaterial sweating cooling structure under different working conditions.

[0014] In the figure: 1. Spectral stealth porous superstructure layer; 2. Infrared thermal stealth porous superstructure layer; 3. Hydrogel filling layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0016] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "top / bottom end", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0017] Example, referring to Figures 1 to 5 , a sweating cooling composite thermal protection structure based on porous metamaterials, including a layered metamaterial composite structure body. The layered metamaterial composite structure body sequentially includes the following components from top to bottom: a spectral stealth porous superstructure layer 1, an infrared thermal stealth porous superstructure layer 2, and a hydrogel filling layer 3. It comprehensively utilizes the phase change sweating cooling of the porous medium of the metamaterial, the stable and continuous coolant supply of the hydrogel solid cooling medium, and the spectral stealth and infrared thermal stealth properties of the metamaterial to achieve the multi-functional integration of sweating cooling active thermal protection, thermal stealth, and spectral stealth. The spectral stealth porous superstructure layer 1 uses the principle of an optical invisibility cloak. According to the requirements of the stealth band, the geometric shape and arrangement of the micro-nano structure units are designed using transformation optics theory. By regulating the geometric shape and arrangement of the micro-nano structure units, spectral stealth in the visible light, infrared, and microwave bands is achieved.

[0018] The spectral stealth porous superstructure layer 1 can be prepared by selecting existing different processing technologies, such as 3D printing technology, electron beam lithography (EBL), or nanoimprinting technology, etc. A circular or I-shaped array structure is processed on a metal substrate (such as gold, silver, copper). By regulating the characteristic size of the internal shape of each unit, the reflection, absorption, or scattering of the incident light wave is achieved, and the stealth design of a specific band is achieved. The material is selected as a metal-dielectric composite material. The thickness of the spectral stealth porous superstructure layer 1 is 2 - 6 mm, such as 2 mm, 4 mm, 6 mm, etc., and corresponding adjustments need to be made according to the overall requirements of the aircraft wall thickness.

[0019] The infrared thermal stealth porous superstructure layer 2 is a double-layer porous structure, prepared by 3D printing technology, and the material is a high-temperature resistant nickel-based alloy porous material.

[0020] Figure 2 , Figure 3 , Figure 4There are infrared thermal stealth porous superstructure layers 2 with three different structures. The upper layer has a lower porosity (e.g., ɛ = 0.2) and a higher effective thermal conductivity; the lower layer has a higher porosity (e.g., ɛ = 0.8) and a lower effective thermal conductivity. The high porosity of the lower layer provides space for hydrogel filling. The liquid working medium in the hydrogel absorbs heat through phase change in this layer, and the generated gaseous working medium flows inside the porous structure with a lower porosity in the upper layer for sufficient convective heat transfer, taking away most of the heat to achieve an efficient active cooling effect. The infrared thermal stealth porous superstructure layer 2 has anisotropic thermal conductivity through micro-nano structure design, accelerating the transfer of surface heat flux in the horizontal direction and transferring heat to the coolant phase change layer in the vertical direction, triggering the sweating cooling mechanism, effectively eliminating local high temperature on the surface, quickly reducing the average temperature of the solid surface, and reducing the amount of thermal radiation, so as to achieve efficient thermal protection while realizing the infrared thermal stealth function.

[0021] Figure 5 The numerical simulation results of the total thermal radiation of the leading edge of the aircraft without cooling, single sweating cooling, and metamaterial sweating cooling structures under three working conditions with total temperatures of 1209K, 1727K, and 2361K respectively are shown. The porous metamaterial structure greatly reduces the surface temperature of the structure and the amount of thermal radiation, achieving the thermal stealth effect. The overall thickness of the infrared thermal stealth porous superstructure layer 2 is 16 mm, and the thicknesses of the porous structures with different porosities in the upper and lower layers are the same, both 8 mm. The spectral stealth porous superstructure layer 1 is prepared by 3D printing technology.

[0022] The infrared thermal stealth porous superstructure layer 2 is a double-layer porous structure. The upper layer has a low porosity (e.g., ɛ = 0.2), and the lower layer has a high porosity (e.g., ɛ = 0.8). The high porosity of the lower layer provides space for hydrogel filling.

[0023] The infrared thermal stealth porous superstructure layer 2 has anisotropic thermal conductivity through micro-nano structure design. It has a high thermal conductivity along the horizontal direction, which can quickly transfer heat in the horizontal direction to avoid local high temperature; the thermal conductivity distribution is uneven along the vertical direction. The high thermal conductivity of the upper layer can quickly transfer heat to the hydrogel filling layer 3, quickly triggering sweating cooling, improving the active thermal protection effect. At the same time, the low thermal conductivity of the lower layer can block the further downward transfer of heat, maintaining the temperature of the internal structure (such as electronic components) below the boiling point, reducing the surface temperature of the structure, improving the comprehensive thermal protection efficiency, and achieving an efficient infrared thermal stealth effect.

[0024] The material of the infrared thermal stealth porous superstructure layer 2 can be selected from ceramic matrix composites or high-temperature resistant nickel-based alloy porous materials. The thickness of the infrared thermal stealth porous superstructure layer 2 is 10 - 20 mm.

[0025] The hydrogel filling layer 3 selects a hydrogel material with high heat absorption capacity and phase change characteristics as a solid coolant and fills it in the lower pores of the infrared stealth porous superstructure layer. After absorbing heat, the hydrogel undergoes a phase change and transforms into a liquid or gaseous coolant, which penetrates to the surface through the transpiration cooling process and evaporates to absorb heat, thereby reducing the surface temperature of the structure.

[0026] The hydrogel filling layer 3 selects a hydrogel material with high heat absorption capacity and phase change characteristics as a solid coolant and fills it in the lower pores of the infrared stealth porous superstructure layer. The hydrogel is prepared by adding high water absorption resin particles (SAP-50, Usolf) with a mesh size of 50 to deionized water according to a mass ratio of 1:100. After absorbing heat, the hydrogel undergoes a phase change and transforms into a liquid or gaseous coolant, which penetrates to the surface through the transpiration cooling process, evaporates to absorb heat and dissipates heat by convection, thereby reducing the surface temperature of the structure. The thickness of the hydrogel filling layer 3 is 5-10 mm.

[0027] The metamaterial optical stealth-infrared stealth integrated transpiration cooling thermal protection structure of the present invention innovatively integrates three major functions: infrared spectral stealth, infrared thermal stealth, and transpiration cooling active thermal protection. The metamaterial optical stealth-infrared thermal stealth integrated transpiration cooling thermal protection structure takes the infrared thermal stealth superstructure porous material as the core, and realizes the anisotropic thermal conductivity characteristics of the infrared thermal stealth porous superstructure layer 2 through micro-nano structure design and different porosity distributions. This design can accelerate the transfer of surface heat flux in the horizontal direction and the heat transfer to the coolant phase change layer in the vertical direction, trigger the transpiration cooling mechanism, effectively eliminate local high temperatures on the surface, quickly reduce the average surface temperature, and reduce the amount of thermal radiation, so as to achieve efficient thermal protection while realizing the infrared thermal stealth function. Combining with the surface spectral stealth porous superstructure layer 1 also takes into account the spectral stealth requirements. This multi-functional integrated design provides a new idea for meeting the multi-task requirements in complex thermal environments.

[0028] The metamaterial optical stealth-infrared stealth integrated transpiration cooling thermal protection structure of the present invention can effectively meet the spectral stealth requirements. The spectral stealth porous superstructure layer 1 of this structure is based on the principle of an optical stealth cloak, and designs the geometric shape and arrangement of micro-nano structure units through transformation optics theory, thereby regulating the optical characteristics of the structure surface and realizing spectral stealth in the visible light, infrared, and microwave bands. By integrating the optical stealth function on an aircraft, the battlefield concealment of the aircraft can be significantly improved, and the possibility of being detected and intercepted by the enemy can be greatly reduced, having broad application prospects in the military, armed, aerospace fields.

[0029] The metamaterial optical-infrared integrated sweating cooling thermal protection structure of the present invention can effectively meet the requirements of infrared thermal stealth. The infrared thermal stealth porous superstructure layer 2 of this structure can achieve non-uniform thermal conductivity in the porous region through the micro-nano structure design of the metamaterial: the upper porous medium has a higher thermal conductivity, while the lower porous medium maintains a lower thermal conductivity, so that the heat conduction performance of the porous structure is different in different directions. Specifically, the infrared thermal stealth porous superstructure layer 2 has a high thermal conductivity along the horizontal direction, which can quickly transfer heat in the horizontal direction and avoid local high temperature; the thermal conductivity distribution is uneven along the vertical direction. The high thermal conductivity of the upper layer can quickly transfer heat to the hydrogel filling layer 3, quickly trigger sweating cooling, improve the active thermal protection effect, and at the same time, the low thermal conductivity of the lower layer can block the further downward transfer of heat and maintain the temperature of the internal structure (such as electronic components) below the boiling point. This design can significantly reduce the surface temperature of the structure, improve the comprehensive thermal protection efficiency, and at the same time achieve excellent infrared thermal stealth effect.

[0030] The present invention uses hydrogel as a coolant, which can significantly improve the stability of the thermal protection system. Compared with other traditional liquid coolants, hydrogel not only has a larger latent heat of phase change, but also can fill the inside of the complex porous structure without damaging the micro-nano structure. During the sweating cooling process, the hydrogel absorbs heat and undergoes a phase change inside the porous structure, and the generated gaseous coolant can be released smoothly, avoiding the pressure fluctuations caused by the boiling of the liquid coolant, effectively solving the periodic thermal fluctuations and instability problems when using liquid water for traditional sweating cooling, and significantly improving the stability of the thermal protection system.

[0031] The present invention uses hydrogel as an alternative coolant for cooling, which can reduce the weight of the thermal protection system and achieve the purpose of lightweight. The hydrogel is stored in the porous structure in solid form, and no additional pump is required to drive the output of the coolant, which can significantly reduce the weight of the overall thermal protection system and save the energy consumption of the system.

[0032] The present invention uses hydrogel as an alternative coolant for cooling, which can achieve the adaptive supply of the coolant and avoid the complexity of coolant regulation. As a typical temperature-sensitive material, hydrogel can quickly release a large amount of coolant in the high-temperature region to cope with the high heat flux density; while in the low-temperature region, the release amount of the coolant is significantly reduced, which can adapt to the thermal protection requirements of different regions, reduce the waste of the coolant, improve the utilization rate of the coolant, and achieve precise regulation of the coolant distribution.

[0033] The integrated sweating cooling thermal protection structure for metamaterial optical stealth and infrared stealth of the present invention can effectively reduce the frictional resistance and achieve the purpose of drag reduction. The overall structure is a three-dimensional porous structure. The gaseous cooling working medium generated after the hydrogel layer absorbs heat and undergoes a phase change seeps out through the porous structure, forming a stable gas film on the outer surface of the solid structure, significantly reducing the viscous shear stress between the solid surface and the external fluid, thereby reducing the frictional resistance.

[0034] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A sweat-cooling composite thermal protection structure based on porous metamaterials, comprising a layered metamaterial composite structure body, characterized in that: The layered metamaterial composite structure body comprises the following components from top to bottom: a spectrally stealthy porous superstructure layer (1), an infrared thermally stealthy porous superstructure layer (2) and a hydrogel filling layer (3).

2. The sweat-cooling composite thermal protection structure based on porous metamaterials according to claim 1, characterized in that: The spectrally invisible porous superstructure layer (1) is based on the principle of optical invisible cloak, according to the invisible band requirements, and uses transformation optics theory to design the geometric shape and arrangement of micro-nanostructure units; By regulating the geometric shape and arrangement of micro-nano structural units, spectral invisibility in the visible light, infrared and microwave bands can be achieved.

3. The sweat-cooling composite thermal protection structure based on porous metamaterials according to claim 1, characterized in that: The material of the spectral stealth porous superstructure layer (1) is a metal material-medium composite metamaterial, wherein the metal material includes copper, silver, and aluminum, and the dielectric material includes silicon dioxide, silicon nitride, and aluminum oxide; The preparation method of the spectrally stealthy porous superstructure layer (1) comprises 3D printing technology, electron beam lithography and nanoimprint technology; The spectrally stealthy porous superstructure layer (1) has a thickness of 2-6 mm.

4. The sweat-cooling composite thermal protection structure based on porous metamaterials according to claim 1, characterized in that: The infrared thermal stealth porous superstructure layer (2) is a double-layer porous structure, comprising an upper structure with low porosity and a lower structure with high porosity, wherein the high porosity of the lower structure provides space for hydrogel filling.

5. The sweat-cooling composite thermal protection structure based on porous metamaterials according to claim 1, characterized in that: The infrared thermal stealth porous superstructure layer (2) comprises a ceramic-based composite material and a high-temperature resistant nickel-based alloy porous material; The infrared thermal stealth porous superstructure layer (2) has a thickness of 10-20 mm.

6. The sweat-cooling composite thermal protection structure based on porous metamaterials according to claim 1, characterized in that: The hydrogel filling layer (3) is located in the lower structure of the infrared thermal stealth porous superstructure; The hydrogel filling layer (3) is made of a hydrogel material with high heat absorption capacity and phase change characteristics as a solid coolant, and is filled in the pores of the lower structure of the infrared stealth porous superstructure layer.

7. The sweat-cooling composite thermal protection structure based on porous metamaterials according to claim 1, characterized in that: The hydrogel filling layer (3) is made of 50-mesh superabsorbent resin particles, which are added to deionized water at a mass ratio of 1:100 to prepare the hydrogel; The thickness of the hydrogel filling layer (3) is 5-10 mm.

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