CN113978046B - A kind of thermal protection structure and preparation method thereof - Google Patents

Abstract

The invention provides a thermal protection structure and a preparation method thereof, wherein the thermal protection structure comprises a thermal insulation layer, a cavity layer and a skin which are sequentially arranged, wherein the thermal insulation layer is arranged on the outer surface of an inner cabin of an aircraft; the heat insulation layer comprises a porous heat insulation structure, temperature-sensitive hydrogel arranged in the porous heat insulation structure and a cooling working medium adsorbed in the temperature-sensitive hydrogel; when the thermal protection structure is not subjected to thermal protection, the temperature-sensitive hydrogel is in a swelling state and is used for adsorbing a cooling working medium in the temperature-sensitive hydrogel in a solid-phase form; when the thermal protection structure is used for thermal protection, the temperature-sensitive hydrogel absorbs heat radiated inwards by the skin and the cavity layer, so that the thermal protection structure is in a deswelling state, the existence form of the cooling working medium is sequentially changed from a solid phase to a liquid phase and a gas phase, and the gas phase cooling working medium is discharged after being released to the cavity layer. The thermal protection structure provided by the invention has excellent thermal protection performance.

Description

A kind of thermal protection structure and preparation method thereof

technical field

The invention relates to the technical field of thermal protection, in particular to a thermal protection structure and a preparation method thereof.

Background technique

Today, the high-speed flight technology of aircraft has greatly improved the ability of human beings to explore space, enter space, control space and use space, which has special military strategic significance and important scientific value. However, regardless of the near space hypersonic vehicle or the spacecraft entering or returning from interstellar exploration, when re-entry or flight at hypersonic speed (> Mach 5) in the atmosphere, due to the harsh aerodynamic heating environment, the vehicle or spacecraft will face "New thermal barrier" is a key technical problem, and developing thermal protection mechanisms to guide the design and preparation of aircraft thermal protection systems is an effective way to solve this problem.

The thermal protection mechanism is a special mechanism dedicated to the thermal protection of aircraft, and it is a kind of mechanism that includes thermal protection mechanism (for example, based on material properties, physicochemical effects or structural principles, etc.) and system structure and its working principle. At present, the thermal protection mechanisms adopted by active or already-tested hypersonic vehicles (such as X-15, X-37B, Apollo return capsule, X-43A and SHEFEX II) can be classified into passive types (such as heat sink, thermal insulation, etc.) structure), semi-passive (eg ablation, heat pipes) and active (eg working fluid, cooling flow). These traditional thermal protection mechanisms have common characteristics, and all rely on the dissipation, dissipation, resistance, and resistance of the material or structure to achieve thermal protection.

However, near-space hypersonic vehicles will develop in the direction of high speed, wide airspace, long endurance and repeatability in the future. The environment will become more severe, and the thermal barrier problem faced by aircraft will become more prominent. It is difficult to meet the thermal protection needs of future hypersonic aircraft only by relying on traditional thermal protection mechanisms.

SUMMARY OF THE INVENTION

The embodiments of the present invention provide a thermal protection structure and a preparation method thereof, which can provide a thermal protection structure to meet the thermal protection requirements of future hypersonic aircraft.

In a first aspect, the present invention provides a thermal protection structure, the thermal protection structure comprises a thermal insulation layer, a cavity layer and a skin arranged in sequence, the thermal insulation layer is arranged on the outer surface of the interior cabin of the aircraft;

The thermal insulation layer includes a porous thermal insulation structure, a temperature-sensitive hydrogel disposed in the porous thermal insulation structure, and a cooling medium adsorbed in the temperature-sensitive hydrogel;

When the thermal protection structure is not thermally protected, the temperature-sensitive hydrogel is in a swollen state, and is used for adsorbing the cooling working substance in the temperature-sensitive hydrogel in the form of a solid phase;

When the thermal protection structure is thermally protected, the temperature-sensitive hydrogel absorbs the heat radiated inward from the skin and the cavity layer, so that it is in a de-swelling state for cooling the cooling The existing form of the working medium is sequentially transformed from a solid phase to a liquid phase and a gas phase, and the cooling working medium in the gas phase is released into the cavity layer and then discharged.

The purpose of the present invention is to provide an active and passive synergistic thermal protection mechanism for the long-term and repeatable thermal protection structure required by the next generation of hypersonic aircraft, specifically by increasing inward radiation heat dissipation (passive) and solid state. The thermal protection mechanism of the phase-water phase change heat dissipation (active) synergistic effect realizes thermal protection.

Passive: The traditional thermal protection structure mainly realizes heat dissipation through the external radiation of the outer skin (outside), and the present invention adds a cavity layer between the skin and the heat insulating material on the basis of the external radiation, so that the inner side of the skin can also radiate to the outside. Internal radiation heat, through the modification of the inner surface of the skin, the radiation coefficient of the inner side of the skin can be greatly improved, up to 0.9, which increases the internal radiation dissipation on the basis of traditional thermal protection, and achieves improved thermal protection. The purpose of the thermal efficiency of the structure;

Active: water has the highest latent heat of phase change and becomes the best cooling medium for phase change cooling, but the fluidity and storage properties of water require a series of complex auxiliary structures such as sealing, storage, and anti-corrosion in the thermal protection structure. As a result, it cannot be used in practical engineering thermal protection structures. In order to solve this problem, the present invention adopts solid phase water to replace traditional liquid phase water, and uses temperature-sensitive hydrogel and inorganic-organic assembly technology to turn liquid phase water into solid phase water small particles and fill them into the lower inorganic heat insulating material. Compare and choose alumina porous insulation material. The solid-phase water particles are fixed in the micropores of the porous medium by chemical dendrites. After the solid-phase hydrogel is filled, it can be tightly connected with the porous thermal insulation material. When the temperature in the cavity increases due to radiation, the solid phase water will be slowly released to form liquid phase water, and the liquid phase water will evaporate into water vapor immediately after being heated, and then the heat will be taken away through this liquid-gas phase change.

Through the synergistic effect of internal radiation heat dissipation (passive) and solid-phase water phase change heat dissipation (active), the thermal protection capability of the thermal protection structure can be greatly improved. The thickness of the cavity between the skin and the porous medium, the distribution and pore size of the micropores inside the porous medium, and the content of solid water can be designed and adjusted according to the needs of thermal protection.

The thermal protection mechanism of the present invention is an active-passive synergistic thermal protection mechanism. On the basis of giving full play to the radiation heat dissipation of the outer surface, not only the internal radiation heat dissipation phase is increased, but more importantly, the phase change heat dissipation of the solid phase water is increased. The amount of heat is 30 to 50 times that of radiation heat dissipation, and its thermal protection effect is better than other single active or passive thermal protection machines and structures such as ceramic-based adiabatic heat protection, sweat cooling and film cooling.

The thermal protection structure based on the active/passive synergistic thermal protection mechanism of the present invention can be applied to heat-resistant structures such as the leading edge and nose cone of hypersonic aircraft wings, and can also be applied to large-area areas on the windward side, with a thermal load of 100-10 MW/m ² , and not less than 30 minutes;

According to the conditions of different thermal loads, the thickness of the thermal protection structure provided by the present invention is 10-100 mm; the temperature of the back wall of the thermal protection structure provided by the present invention is lower than 100° C.; Bearing integrated features.

Preferably, the thermal protection structure further comprises screws and nuts, and the heat insulating layer and the skin are fixed on the outer surface of the inner cabin of the aircraft through the cooperation of the screws and the nuts.

Preferably, both the screw and the nut are made of alumina ceramics.

Preferably, the porous heat insulating structure is made of alumina ceramics.

Preferably, in the thermal protection structure according to any one of the above first aspects, the cooling medium comprises water.

In a second aspect, the present invention provides a method for preparing a thermal protection structure, comprising:

The temperature-sensitive hydrogel and the porous thermal insulation structure are placed in a container containing a cooling medium, so that the temperature-sensitive hydrogel enters the porous thermal insulation structure; wherein the temperature of the cooling medium is is a first preset temperature, and at the first preset temperature, the temperature-sensitive hydrogel is in a de-swelling state;

lowering the temperature of the cooling working medium to a second preset temperature, so that the cooling working medium is adsorbed in the temperature-sensitive hydrogel in the form of a solid phase to obtain a thermal insulation layer; wherein, in the Under the second preset temperature, the temperature-sensitive hydrogel is in a swollen state;

The heat insulating layer and the skin are fixed, and a cavity layer is arranged between the heat insulating layer and the skin to form a heat protection structure; wherein, the heat insulating layer is arranged outside the inner cabin of the aircraft on the surface.

The purpose of the present invention is to provide an active and passive synergistic thermal protection mechanism for the long-term and repeatable thermal protection structure required by the next generation of hypersonic aircraft, specifically by increasing inward radiation heat dissipation (passive) and solid state. The thermal protection mechanism of the phase-water phase change heat dissipation (active) synergistic effect realizes thermal protection.

Passive: The traditional thermal protection structure mainly realizes heat dissipation through the external radiation of the outer skin (outside), and the present invention adds a cavity layer between the skin and the heat insulating material on the basis of the external radiation, so that the inner side of the skin can also radiate to the outside. Internal radiation heat, through the modification of the inner surface of the skin, the radiation coefficient of the inner side of the skin can be greatly improved, up to 0.9, which increases the internal radiation dissipation on the basis of traditional thermal protection, and achieves improved thermal protection. The purpose of the thermal efficiency of the structure;

Active: water has the highest latent heat of phase change and becomes the best cooling medium for phase change cooling, but the fluidity and storage properties of water require a series of complex auxiliary structures such as sealing, storage, and anti-corrosion in the thermal protection structure. As a result, it cannot be used in practical engineering thermal protection structures. In order to solve this problem, the present invention adopts solid phase water to replace traditional liquid phase water, and uses temperature-sensitive hydrogel and inorganic-organic assembly technology to turn liquid phase water into solid phase water small particles and fill them into the lower inorganic heat insulating material. Compare and choose alumina porous insulation material. The solid-phase water particles are fixed in the micropores of the porous medium by chemical dendrites. After the solid-phase hydrogel is filled, it can be tightly connected with the porous thermal insulation material. When the temperature in the cavity increases due to radiation, the solid phase water will be slowly released to form liquid phase water, and the liquid phase water will evaporate into water vapor immediately after being heated, and then the heat will be taken away through this liquid-gas phase change.

Through the synergistic effect of internal radiation heat dissipation (passive) and solid-phase water phase change heat dissipation (active), the thermal protection capability of the thermal protection structure can be greatly improved. The thickness of the cavity between the skin and the porous medium, the distribution and pore size of the micropores inside the porous medium, and the content of solid water can be designed and adjusted according to the needs of thermal protection.

The thermal protection mechanism of the present invention is an active-passive synergistic thermal protection mechanism. On the basis of giving full play to the radiation heat dissipation of the outer surface, not only the internal radiation heat dissipation phase is increased, but more importantly, the phase change heat dissipation of the solid phase water is increased. The amount of heat is 30 to 50 times that of radiation heat dissipation, and its thermal protection effect is better than other single active or passive thermal protection machines and structures such as ceramic-based adiabatic heat protection, sweat cooling and film cooling.

The thermal protection structure based on the active/passive synergistic thermal protection mechanism of the present invention can be applied to heat-resistant structures such as the leading edge and nose cone of hypersonic aircraft wings, and can also be applied to large-area areas on the windward side, with a thermal load of 100-10 MW/m ² , and not less than 30 minutes;

According to the conditions of different thermal loads, the thickness of the thermal protection structure provided by the present invention is 10-100 mm; the temperature of the back wall of the thermal protection structure provided by the present invention is lower than 100° C.; Bearing integrated features.

Preferably, the fixing of the thermal insulation layer and the skin includes:

The thermal insulation layer and the skin are fixed by the cooperation of screws and nuts.

Preferably, both the screw and the nut are made of alumina ceramics.

Preferably, the porous heat insulating structure is made of alumina ceramics.

Preferably, in the method for preparing a thermal protection structure according to any one of the above second aspects, the cooling medium comprises water.

Compared with the prior art, the present invention at least has the following beneficial effects:

By arranging a thermal protection structure including a thermal insulation layer, a cavity layer and a skin on the outer surface of the inner cabin of the aircraft, it has excellent thermal protection performance.

The skin and cavity in the thermal protection structure make it have passive thermal protection function. The passive thermal protection mechanism is that the skin absorbs the external heat and then releases the absorbed heat by means of thermal radiation. Among them, there are two ways of skin thermal radiation, one is to release external radiation from the skin to the external environment, and the other is to release internal radiation to the cavity. By arranging the cavity layer in the invention, the skin can radiate heat to the cavity layer while radiating heat to the outside, thereby adding a way of inward radiation on the basis of traditional thermal protection, thereby improving the Thermal protection efficiency of passive thermal protection.

The thermal insulation layer in the thermal protection structure includes a porous thermal insulation structure, a temperature-sensitive hydrogel arranged in the porous thermal insulation structure, and a cooling medium adsorbed in the temperature-sensitive hydrogel. The pores in the porous thermal insulation structure can accommodate the temperature-sensitive hydrogel, which can absorb the liquid-phase cooling medium and convert it into the solid phase.

Thermal insulation and cavities in the thermal protection structure make it active thermal protection. When the thermal protection structure is thermally protected, the temperature-sensitive hydrogel absorbs the heat radiated inward from the skin and the cavity layer, making it in a de-swelling state, which is used to sequentially transform the existence of the cooling medium from the solid phase. into liquid phase and gas phase, and the cooling working medium in the gas phase is released into the cavity layer and then discharged. The thermal insulation layer contains thermosensitive hydrogel. When the temperature of the thermal insulation layer is lower than the lower critical solution temperature (LCST) of thermosensitive hydrogel, the thermosensitive hydrogel is in a swollen state and absorbs cooling work. In the process of using the thermal protection structure, the temperature of its use environment is higher than the lower critical solution temperature (LCST) of the temperature-sensitive hydrogel, and the temperature-sensitive water The gel absorbs heat and exhibits a de-swelling state, transforming the cooling medium from solid phase to liquid phase and releasing it. Then, the liquid-phase cooling medium continues to absorb heat and further transform into gas phase and release it into the cavity for discharge, thereby achieving excellent thermal protection. Function.

In addition, the thermal protection structure provided by the present invention can be reused. Through the reversible swelling and deswelling properties of the temperature-sensitive hydrogel in the thermal insulation layer with the change of the ambient temperature, the repeated use of the thermal protection structure can be realized. The thermal protection structure after use can make the temperature-sensitive hydrogel in it swell and absorb the cooling medium by means of cooling down and supplementing the cooling medium, so as to restore the excellent thermal protection performance.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are For some embodiments of the present invention, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a schematic diagram of the principle of a thermal protection structure provided by an embodiment of the present invention;

2 is a flowchart of a method for preparing a thermal protection structure provided by an embodiment of the present invention;

3(a) is a perspective view of a thermal protection structure provided by an embodiment of the present invention;

3(b) is a partial cross-sectional view of a thermal protection structure provided by an embodiment of the present invention;

FIG. 4 is a comparison diagram of the heat protection effect of the thermal protection structure provided in Example 1 of the present invention and the thermal protection structure provided in Comparative Example 1. FIG.

In the picture:

1. Skin; 2. Cavity layer; 3. Insulation layer; 4. Bottom plate; 5. Screw; 6. Nut.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are protected by the present invention. scope.

As shown in Figure 1, Figure 3 (a) and Figure 3 (b), the present invention provides a thermal protection structure, the thermal protection structure comprises a thermal insulation layer 3, a cavity layer 2 and a skin 1 arranged in sequence, The thermal layer 3 is arranged on the bottom plate 4;

The thermal insulation layer 3 includes a porous thermal insulation structure, a temperature-sensitive hydrogel disposed in the porous thermal insulation structure, and a cooling medium adsorbed in the thermally sensitive hydrogel;

When the thermal protection structure is not thermally protected, the temperature-sensitive hydrogel is in a swollen state, which is used to adsorb the cooling medium in the temperature-sensitive hydrogel in the form of a solid phase;

When the thermal protection structure performs thermal protection, the temperature-sensitive hydrogel absorbs the heat radiated inward from the skin 1 and the cavity layer 2, making it in a de-swelling state, and is used to change the existence of the cooling medium from the solid phase. It is sequentially transformed into liquid phase and gas phase, and the cooling working medium in the gas phase is released to the cavity layer 2 and then discharged.

It should be noted that the bottom plate 4 is a part of the outer surface of the inner cabin of the aircraft, and the commonly used material is aluminum alloy.

In the present invention, the bottom plate 4 is provided with a heat protection structure including the heat insulation layer 3, the cavity layer 2 and the skin 1, so that it has excellent heat protection performance.

The skin 1 and the cavity in the thermal protection structure enable it to have a passive thermal protection function. The passive thermal protection mechanism is that the skin 1 absorbs external heat and then releases part of the absorbed heat through thermal radiation. Among them, there are two ways for the skin 1 to radiate heat. One is that the skin 1 releases external radiation to the external environment, and the other is to release internal radiation to the cavity. By setting the cavity layer 2 in the present invention, the skin 1 can radiate heat to the cavity layer 2 while radiating heat to the outside, thereby adding a way of inward radiation on the basis of traditional thermal protection. Thus, the thermal protection efficiency of passive thermal protection is improved.

The thermal insulation layer 3 in the thermal protection structure includes a porous thermal insulation structure, a temperature-sensitive hydrogel disposed in the porous thermal insulation structure, and a cooling medium adsorbed in the temperature-sensitive hydrogel. The pores in the porous thermal insulation structure can accommodate the temperature-sensitive hydrogel, which can absorb the liquid-phase cooling medium and convert it into the solid phase.

The thermal insulation layer 3 and the cavity in the thermal protection structure enable it to have an active thermal protection function. When the thermal protection structure performs thermal protection, the temperature-sensitive hydrogel absorbs the heat radiated inward from the skin 1 and the cavity layer 2, making it in a de-swelling state, and is used to change the existence of the cooling medium from the solid phase. It is sequentially transformed into liquid phase and gas phase, and the cooling working medium in the gas phase is released into the cavity layer 2 and then discharged. The thermal insulation layer 3 contains a thermosensitive hydrogel. When the temperature of the thermal insulation layer 3 is lower than the lower critical solution temperature (LCST) of the thermosensitive hydrogel, the thermosensitive hydrogel is in a swollen state, and absorbs the temperature sensitive hydrogel. Cool the working fluid and convert it into a solid phase to obtain the thermal insulation layer 3; during the use of the thermal protection structure, the ambient temperature of the thermal protection structure is higher than the low critical solution temperature (LCST) of the thermosensitive hydrogel, and the temperature is The sensitive hydrogel absorbs heat and exhibits a de-swelling state, and the cooling medium is transformed from a solid phase to a liquid phase and released. Then, the liquid-phase cooling medium continues to absorb heat and further transform into a gas phase and release it into the cavity for discharge, thereby achieving excellent performance. thermal protection.

In addition, the thermal protection structure provided by the present invention can be reused. Through the characteristics of reversible swelling and deswelling of the temperature-sensitive hydrogel in the thermal insulation layer 3 with the change of the ambient temperature, the repeated use of the thermal protection structure can be realized. The thermal protection structure after use can make the temperature-sensitive hydrogel in it swell and absorb the cooling medium by means of cooling down and supplementing the cooling medium, so as to restore the excellent thermal protection performance. In the present invention, the thermal protection structure achieves excellent thermal protection performance through an active-passive coordinated thermal protection mechanism. On the basis of giving full play to the radiation heat dissipation of the outer surface, the internal radiation heat dissipation (passive thermal protection) is added; in addition, the phase change heat dissipation of the solid phase water (active thermal protection) is also added, and the heat dissipation is the outer surface. Radiation heat dissipation 30 to 50 times. The thermal protection structure provided by the invention can ensure that the temperature of the inner and outer surfaces of the aircraft is less than 100° C. for the hypersonic aircraft in the aerodynamic heating environment. Other single active or passive thermal protection mechanisms.

It should be noted that, in the process of de-swelling of the temperature-sensitive hydrogel in the thermal insulation layer 3, the cooling medium continuously absorbs heat through the phase transition process of the solid phase, the liquid phase and the gas phase. - Liquid-gas phase balance, so that the temperature of the thermal insulation layer 3 is kept below the boiling point temperature of the cooling medium until the solid phase cooling medium is exhausted, and the active thermal protection mechanism fails.

In the present invention, the active thermal protection mechanism time can be adjusted by the pore size and pore distribution of the porous thermal insulation structure, the water controlled release rate of the thermosensitive hydrogel, and the quality of the cooling medium.

It should be noted that the cooling medium selected by the traditional active thermal protection structure is liquid phase. Due to the fluidity of the liquid phase cooling medium, placing it in the thermal protection structure requires a series of complex sealing, storage and anticorrosion. Auxiliary structure, making it difficult to apply in practical thermal protection structure. In order to solve this problem, the present invention adds a temperature-sensitive hydrogel to the thermal insulation layer 3, and the temperature-sensitive hydrogel can absorb the cooling medium and convert it into a solid phase, thereby avoiding the need to set it in the thermal protection structure. Auxiliary structure required to store liquid-phase cooling medium. In addition, the active thermal protection mechanism in the thermal protection structure of the present invention is completely triggered automatically by the temperature change, and the thermal protection is realized by the phase change of the cooling medium to absorb heat, and the whole process does not require any sensors and control devices.

The thermal protection structure provided by the present invention can be applied to the leading edge, nose cone and other parts of hypersonic aircraft wings, and can also be applied to a large area on the windward side, and can withstand thermal loads of 100kW/m ² to 10MW/m ² , and the loading time Up to 30min. Among them, the loading time is the effective time of the active thermal protection mechanism.

According to some preferred embodiments, the thermal protection structure further includes screws 5 and nuts 6 , and the thermal insulation layer 3 and the skin 1 are fixed on the bottom plate 4 through the cooperation of the screws 5 and the nuts 6 .

According to some preferred embodiments, both the screw 5 and the nut 6 are made of alumina ceramics.

According to some preferred embodiments, the porous insulating structure is made of alumina ceramics.

As shown in Fig. 3(a) and Fig. 3(b), the thermal protection structure can use screws 5 and nuts 6 to cooperate to fix the skin 1, the heat insulation layer 3 and the bottom plate 4 in sequence, wherein the nuts 6 It is fixed on both sides of the skin 1 to retain the cavity layer 2 between the thermal insulation layer 3 and the skin 1 .

In the present invention, the skin 1 is made of a high temperature alloy plate; the porous heat insulation structure and the screw 5 and the nut 6 are made of alumina ceramic material, and the alumina ceramic material has excellent heat insulation. Compared with other porous insulating materials (such as zirconia ceramic materials), alumina ceramic materials have lower unit price and more uniform pore distribution.

According to some preferred embodiments, in the thermal protection structure of any one of the above-mentioned first aspect, the cooling medium includes water.

It should be noted that, because the latent heat of water phase change is the highest, water is selected as the best cooling medium for phase change cooling.

As shown in Figure 2, the present invention also provides a preparation method of a thermal protection structure, comprising:

The temperature-sensitive hydrogel and the porous thermal insulation structure are placed in a container containing a cooling medium, so that the temperature-sensitive hydrogel enters the porous thermal insulation structure; wherein the temperature of the cooling medium is a first preset temperature , at the first preset temperature, the temperature-sensitive hydrogel is in a de-swelling state;

lowering the temperature of the cooling working medium to a second preset temperature, so that the cooling working medium is adsorbed in the temperature-sensitive hydrogel in the form of a solid phase to obtain a thermal insulation layer; wherein, at the second preset temperature, The thermosensitive hydrogel is in a swollen state;

The heat insulation layer and the skin are fixed, and a cavity layer is arranged between the heat insulation layer and the skin to form a thermal protection structure; wherein, the heat insulation layer is arranged on the bottom plate. It should be noted that the first preset temperature is slightly higher than LCST (low critical dissolution temperature of thermosensitive hydrogel in the thermal insulation layer), and the second preset temperature is lower than LCST. When the temperature of the thermosensitive hydrogel is higher than LCST, it is in a de-swelling state, and there is no water inside; when the temperature of the thermosensitive hydrogel is lower than LCST, it is in a swollen state, which can absorb water in the liquid phase and release it in the water. Solid water is formed inside.

In the present invention, when the cooling medium is at the first preset temperature, the temperature-sensitive hydrogel in the container is in a liquid-phase de-swelling state. The sensitive hydrogel macromolecules are combined with the inner wall of the pores of the porous thermal insulation structure by means of grafting.

In the present invention, when the temperature of the cooling medium drops to the second preset temperature, the temperature-sensitive hydrogel in the pores of the porous thermal insulation structure is in a swollen state during the cooling process. A large amount of distilled water is absorbed to swell, and the swelling speed increases as the temperature decreases. When the temperature in the container is lowered to the second preset temperature, the temperature-sensitive hydrogel reaches the swelling equilibrium to obtain a thermal insulation layer. By reducing the temperature in the container, the temperature-sensitive hydrogel in the porous thermal insulation structure is swollen by water absorption, and the liquid phase water in the container is converted into solid phase water, and the solid phase water exists in the form of bound water and free water in the temperature in sensitive hydrogels.

The thickness of the thermal protection structure provided by the present invention is 10-100 mm (the thickness includes the bottom plate), and has the functions of heat protection, heat insulation and bearing integration.

It should be noted that the preparation method provided by the present invention has simple structure, low cost, convenient installation, and strong designability, and can design the thickness of the thermal insulation layer, the path and distribution of the micro-channel according to the flight time and the thermal load of the flight corridor. , Cooling working fluid quality to meet the needs of different flight missions.

According to some preferred embodiments, securing the thermal insulation and the skin includes:

The thermal insulation layer and the skin are fixed by the cooperation of screws and nuts.

According to some preferred embodiments, both the screw and the nut are made of alumina ceramic.

According to some preferred embodiments, the porous insulating structure is made of alumina ceramics.

As shown in Figure 3, the thermal protection structure can be used to fix the skin, the heat insulation layer and the bottom plate together in turn by means of screws and nuts. The cavity layer remains between the skin.

In the present invention, the skin is made of high temperature alloy plate; the porous heat insulation structure and the screw nut are made of alumina ceramic material, and the alumina ceramic material has excellent heat insulation. Compared with other porous insulating materials (such as zirconia ceramic materials), alumina ceramic materials have lower unit price and more uniform pore distribution.

According to some preferred embodiments, in the preparation method of any one of the above-mentioned thermal protection structures, the cooling medium includes water.

It should be noted that, because the latent heat of water phase change is the highest, water is selected as the best cooling medium for phase change cooling.

In order to illustrate the technical solutions and advantages of the present invention more clearly, a thermal protection structure and a preparation method thereof will be described in detail below through several embodiments.

Example 1

The temperature-sensitive hydrogel and the porous alumina ceramic plate of 100mm × 100mm × 8mm were placed in a container containing distilled water, so that the temperature-sensitive hydrogel entered the porous alumina ceramic plate; wherein, the temperature of the distilled water was 36 ℃, the temperature-sensitive hydrogel is in a de-swelling state;

lowering the temperature of the distilled water to 25°C, so that the distilled water is adsorbed in the temperature-sensitive hydrogel in the form of a solid phase to obtain a thermal insulation layer; wherein, the temperature-sensitive hydrogel is in a swollen state;

The heat insulation layer, the skin and the bottom plate are fixed by means of screws and nuts to obtain the bottom plate of the thermal protection structure. Among them, the skin is made of 100mm×100mm×5mm high temperature alloy plate, the bottom plate material is made of 100mm×100mm×5mm aluminum alloy plate, and the screw nuts are M4 alumina ceramic screw nuts. Among them, nuts are fixed on both sides of the skin to retain an 8mm cavity layer between the thermal insulation layer and the skin.

The prepared thermal protection structure bottom plate is placed on the thermal insulation felt, and thermocouples are respectively bonded to the outer surface of the skin and the outer surface of the thermal insulation layer, and then placed under a high-power quartz lamp, and the heat flux density is adjusted by the high-power quartz lamp. The temperature of the outer surface of the skin was measured to be 865°C, and the temperature of the outer surface of the thermal insulation layer did not exceed 100°C, and lasted for ³ minutes (the effective time of the active thermal protection mechanism).

Example 2

The preparation method of embodiment 2 is basically the same as that of embodiment 1, and the difference is:

The heat flux density was 0.1 MW/m ² , and the thickness of the porous alumina ceramic plate was 5 mm.

The measured outer surface temperature of the skin is 420°C, and the effective time of the active thermal protection mechanism is 30 minutes.

Example 3

The preparation method of embodiment 3 is basically the same as that of embodiment 1, and the difference is:

The thermal protection structure was placed in a high-frequency plasma wind tunnel, the heat flux density was adjusted to 5MW/m ² , and the thickness of the porous alumina ceramic plate was 15mm.

The measured outer surface temperature of the skin is 870°C, and the effective time of the active thermal protection mechanism is 15 minutes.

Example 4

The preparation method of embodiment 4 is basically the same as that of embodiment 1, and the difference is:

The thermal protection structure was placed in a high-frequency plasma wind tunnel, the heat flux density was adjusted to 10MW/m ² , and the thickness of the porous alumina ceramic plate was 30mm.

The measured outer surface temperature of the skin is 910 °C, and the active thermal protection mechanism is effective for 20 minutes.

Comparative Example 1

Select a 100mm×100mm×5mm superalloy plate as the skin, bond a thermocouple to the outer surface of the skin, place it under a high-power quartz lamp, adjust the heat flux density to 0.9MW/m ² through the high-power quartz lamp, and The thermal assessment test was carried out, and the outer surface temperature of the skin was measured to be 1170°C.

The thermal assessment test data of Examples 1 to 4 and Comparative Example 1 are summarized in Table 1:

Table 1

It can be seen from Examples 1 to 4 that the thermal protection structure provided by the present invention can bear a maximum thermal load of 10W/m ² , and the effective time of the active thermal protection mechanism can reach 30 minutes.

It can also be seen from Examples 1 to 4 that the active thermal protection mechanism in the thermal protection structure of the present invention has an excellent thermal protection effect, and can control the temperature of the inner and outer surfaces of the aircraft to be below 100°C, and can pass through the porous thermal insulation structure. The thickness and heat flux density adjust the time of the active thermal protection mechanism.

It can be seen from Example 1 and Comparative Example 1 (as shown in Figure 4) that the outer surface temperature of the skin of Example 1 is 865°C, and the temperature of the outer surface of the skin of Comparative Example 1 is 1170°C, which proves the thermal protection structure provided by the present invention. The thermal protection effect of the material can be enhanced by internal radiation in the passive thermal protection mechanism.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be The technical solutions described in the foregoing embodiments are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (4)

1. A thermal protection structure is characterized by comprising a thermal insulation layer, a cavity layer and a skin which are sequentially arranged, wherein the thermal insulation layer is arranged on the outer surface of an inner cabin of an aircraft;

the heat insulation layer comprises a porous heat insulation structure, temperature-sensitive hydrogel arranged in the porous heat insulation structure and a cooling working medium adsorbed in the temperature-sensitive hydrogel;

when the thermal protection structure is not subjected to thermal protection, the temperature-sensitive hydrogel is in a swelling state and is used for adsorbing the cooling working medium in the temperature-sensitive hydrogel in the form of existence of bound water and free water;

when the thermal protection structure is subjected to thermal protection, the temperature-sensitive hydrogel absorbs heat radiated inwards by the skin and the cavity layer, so that the temperature-sensitive hydrogel is in a deswelling state, is used for sequentially converting the existence form of the cooling working medium from bound water and free water into a liquid phase and a gas phase, and discharges the gas phase of the cooling working medium after the cooling working medium is released to the cavity layer;

the thermal protection structure further comprises a screw and a nut, and the thermal insulation layer and the skin are fixed on the outer surface of the inner cabin of the aircraft through the matching of the screw and the nut;

The porous heat insulation structure is made of alumina ceramics;

the cooling medium comprises water.

2. The thermal protection structure of claim 1, wherein said screw and said nut are both made of alumina ceramic.

3. A method of making a thermal protective structure, comprising:

placing the temperature-sensitive hydrogel and the porous heat insulation structure in a container containing a cooling working medium so that the temperature-sensitive hydrogel enters the porous heat insulation structure; the temperature of the cooling working medium is a first preset temperature, and the temperature-sensitive hydrogel is in a deswelling state at the first preset temperature;

reducing the temperature of the cooling working medium to a second preset temperature so that the cooling working medium is adsorbed in the temperature-sensitive hydrogel in the form of existence of bound water and free water to obtain a heat insulation layer; wherein, at the second preset temperature, the temperature-sensitive hydrogel is in a swelling state;

fixing the heat insulation layer and the skin, and arranging a cavity layer between the heat insulation layer and the skin to form a thermal protection structure; wherein the insulation layer is disposed on an outer surface of an interior compartment of the aircraft;

Fixing the thermal insulation layer and the skin comprises:

fixing the heat insulation layer and the skin by utilizing the matching of a screw and a nut;

the porous heat insulation structure is made of alumina ceramics;

the cooling working medium comprises water.

4. The method of claim 3, wherein the screw and the nut are made of alumina ceramic.

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