Fractal structure function integrated thermal protection system containing composite phase change material

Abstract

The invention discloses a fractal structure function integrated thermal protection system containing a composite phase change material, which comprises a fractal structure web fixedly arranged on the inner side of an outer plate, an inner plate fixedly arranged on the lower side of the fractal structure web, and a middle partition plate fixedly arranged on the fractal structure web between the outer plate and the inner plate, a cavity between the middle partition plate and the outer plate is filled with a heat insulation material, and a cavity between the middle partition plate and the inner plate is filled with a composite phase change material; through the nano wetting effect of the modified low-melting-point metal-based alloy and the synergistic effect of a micron-sized framework of the expanded graphite, an alloy-graphite two-stage heat conduction network is constructed, the heat conduction coefficient is greatly increased, heat of the fractal-structure web can be rapidly transferred into the composite phase change material to be stored, the problem of thermal short circuit is avoided, and the fractal-structure web is suitable for large-scale production. The thermal protection performance and the temperature uniformity are improved, and reliable guarantee is provided for safe flight of an aircraft in an environment with serious aerodynamic heating.

Description

Technical Field

[0001] The present invention relates to the field of thermal protection technology, and in particular to a fractal structure-functional integrated thermal protection system containing composite phase change materials. Background Art

[0002] When an aircraft flies at high speed, the temperature of the skin surface and its vicinity rises rapidly due to shock wave compression, boundary layer friction and adiabatic stagnation effect. The sharply increased aerodynamic heat can cause material failure, deformation of the body structure, electronic system failure and communication interruption. In order to maintain the stability of the overall or local aerodynamic shape of the aircraft and the normal operation of internal electronic equipment and personnel within the allowable temperature range, it is of great significance to develop an efficient and reliable aerodynamic thermal protection system for high-speed aircraft.

[0003] The traditional corrugated plate integrated thermal protection system combines load-bearing and heat protection functions, has high structural efficiency, and is in line with the design concept of lightweight, low redundancy, and multi-functionality of future aircraft. However, there is a thermal short-circuit problem; that is, heat will always be transferred to the interior of the aircraft through the web structure with higher thermal conductivity, resulting in an increase in internal ambient temperature and increased temperature unevenness.

[0004] Phase change materials have the characteristics of large latent heat, low density, and small volume change. They can be used as heat-absorbing materials to alleviate the thermal short-circuit problem of integrated thermal protection systems, thereby greatly improving the heat insulation performance of the integrated thermal protection systems. However, although common phase change materials can absorb heat through phase change latent heat, they have low thermal conductivity, narrow phase change temperature, and are prone to phase change material leakage when the temperature is too high. Therefore, the present invention proposes a fractal structure functional integrated thermal protection system containing composite phase change materials to solve the problems existing in the prior art. Summary of the Invention

[0005] In response to the above problems, the purpose of the present invention is to propose a fractal structure functional integrated thermal protection system containing a composite phase change material. The fractal structure functional integrated thermal protection system containing a composite phase change material constructs an "alloy-graphite" two-stage thermal conductive network through the synergistic effect of the nano-wetting effect of the modified low-melting-point metal-based alloy and the micron-scale skeleton of the expanded graphite. The thermal conductivity coefficient is greatly improved, and the heat of the fractal structure web can be quickly transferred to the composite phase change material for storage without the problem of thermal short circuit. The thermal protection performance and temperature uniformity are improved, providing reliable protection for the safe flight of aircraft in an environment with severe aerodynamic heating.

[0006] To achieve the purpose of the present invention, the present invention is implemented through the following technical solutions: a fractal structure functional integrated thermal protection system containing composite phase change material, including an outer plate and an inner plate, a fractal structure web is fixed on the inner side of the outer plate, an inner plate is fixed on the lower side of the fractal structure web, an intermediate partition is fixed on the fractal structure web between the outer plate and the inner plate, the cavity between the intermediate partition and the outer plate is filled with thermal insulation material, and the cavity between the intermediate partition and the inner plate is filled with composite phase change material.

[0007] A further improvement is that the outer plates, the middle partition plates and the inner plates are arranged parallel to each other and are supported and fixed by the fractal structure webs.

[0008] A further improvement is that: the fractal structure webs are distributed in a leaf vein shape from outside to inside and adjacent fractal structure webs are parallel to each other, and the fractal structure webs are branched corrugated plate structures.

[0009] A further improvement is that the outer plate, inner plate, fractal structure web and middle partition are all made of silicon carbide or high-temperature alloy and are integrally formed by 3D printing.

[0010] A further improvement is that the thermal insulation material is aerogel with a density of 220kg / m 3 , specific heat capacity is 500 J / kg·K, and thermal conductivity is 0.02 W / m·K.

[0011] A further improvement is that the thermal conductivity of the composite phase change material is 2.31 W·m -1 ·K -1 , latent heat 152.1-207.2kJ / kg, leakage rate <7%.

[0012] A further improvement is that the composite phase change material is composed of 75-95 wt% of paraffin wax, 5 wt% of expanded graphite and 0-20 wt% of modified low melting point metal-based alloy.

[0013] Further improvements are: the paraffin phase transition temperature is 42°C, the latent heat is 207.1 J / g; the expanded graphite purity is ≥99%, and the modified low-melting-point metal-based alloy consists of 50wt% bismuth, 25wt% tin, 12.5wt% cadmium and 12.5wt% chromium, with a melting point of 70°C.

[0014] The beneficial effects of the present invention are as follows: the present invention constructs an "alloy-graphite" dual-stage thermal conductivity network through the synergistic effect of the nano-wetting effect of the modified low-melting-point metal-based alloy and the micron-scale skeleton of the expanded graphite, significantly improving the thermal conductivity. The heat of the fractal structure web can be quickly transferred to the composite phase change material for storage, so that the temperature in the system can be evenly distributed, and the problem of thermal short circuit will not occur.

[0015] The present invention utilizes the characteristics of high specific strength and large surface area of ​​the fractal structure, and contacts with the composite phase change material over a large area, so as to quickly absorb and store the heat transferred from the web of the fractal structure, reduce the heat gradient transferred to the interior of the aircraft, improve the thermal protection performance and temperature uniformity, and provide reliable protection for the safe flight of the aircraft in an environment with severe aerodynamic heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of the present invention.

[0017] Among them: 1. Outer plate; 2. Inner plate; 3. Middle partition; 4. Fractal structure web; 5. Thermal insulation material; 6. Composite phase change material. DETAILED DESCRIPTION

[0018] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the examples. The examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0019] When an aircraft flies at high speed, the temperature of the skin surface and its vicinity rises rapidly due to shock wave compression, boundary layer friction, and adiabatic stagnation effects. Rapidly rising aerodynamic heat can cause material failure, deformation of the airframe, electronic system failure, and communication interruption. To maintain the overall or local aerodynamic shape stability of the aircraft and ensure the normal operation of internal electronic equipment and personnel within the permitted temperature range, it is of great significance to develop an efficient and reliable aerodynamic thermal protection system for high-speed aircraft. The corrugated plate integrated thermal protection system combines load-bearing and heat protection functions, has high structural efficiency, and is in line with the design concept of lightweight, low-redundancy, and multifunctional future aircraft. However, it suffers from a thermal short-circuit problem. Heat is always transferred to the interior of the aircraft through the web structure with high thermal conductivity, resulting in an increase in internal ambient temperature and increased temperature non-uniformity.

[0020] Phase change materials, with their high latent heat, low density, and minimal volume change, can be used as heat absorbers to mitigate thermal short-circuiting issues in integrated thermal protection systems, significantly improving their thermal insulation performance. However, while common phase change materials can absorb heat through latent heat, they suffer from low thermal conductivity, a narrow phase transition temperature, and a tendency to leak at high temperatures. The thermal conductivity of phase change materials is often increased by adding substrates or carrier materials, such as graphene, metal oxides, and metal foams, to regulate the transition temperature and optimize the phase change process. Experimental studies have shown that the thermal conductivity of a copper-based porous framework / paraffin wax composite prepared by vacuum impregnation is up to 15 times higher than that of the base phase change material. Numerical simulations further confirm that the topological optimization design of the porous metal framework effectively enhances the thermal energy transfer efficiency during the phase change process, improving the temperature uniformity of the composite system by over 76% and shortening the heat storage period by 42%-58%.

[0021] Example

[0022] Based on the above, this embodiment provides a fractal structure function integrated thermal protection system containing composite phase change materials. Figure 1 As shown, it comprises an outer panel 1, an inner panel 2, a fractal structure web 4, a middle partition 3, a thermal insulation material 5, and a composite phase change material 6. The outer panel 1, the middle partition 3, and the inner panel 2 are parallel to each other. The middle partition 3 is located between the outer panel 1 and the inner panel 2, dividing the area enclosed by the outer panel 1 and the inner panel 2 into two parts. The first part is close to the outer panel 1 and is used to accommodate the thermal insulation material 5, and the second part is close to the inner panel 2 and is used to accommodate the composite phase change material 6. The fractal structure web 4 is in the shape of a fractal leaf vein and runs through the entire cavity. It serves as a supporting structure for the outer panel 1, the inner panel 2, and the middle partition 3, and connects the outer panel 1, the middle partition 3, and the inner panel 2 into a whole.

[0023] In this embodiment, the outer plate 1, the fractal structure web 4, the middle partition 3, and the inner plate 2 are made of silicon carbide ceramic or high-temperature alloy and are manufactured in an integrated manner by 3D printing. The spatial distribution and functions of each component are as follows:

[0024] Outer plate 1: Located at the outermost layer of the thermal protection system, it directly contacts the external environment and primarily bears the aerodynamic and thermal loads generated by high-speed airflow. When the aircraft is flying at high speed, the heat generated by the high-speed airflow directly acts on outer plate 1. Some of the heat on outer plate 1 is then radiated back to the outside world, while the remaining heat is transferred into the aircraft through the fractal-structured web 4.

[0025] Fractal web 4: Located between the outer panel 1 and the inner panel 2, its leaf-vein-like shape runs through the entire cavity, connecting the outer panel 1, inner panel 2, and intermediate partition 3 into a single unit. Its primary function is to transfer the uniformly distributed aerodynamic loads on the outer panel 1 to the inner panel 2. Furthermore, the fractal web 4 has a much higher thermal conductivity than the insulation material 5. Therefore, heat from the outer panel 1 is primarily transferred into the aircraft through the fractal web 4.

[0026] Middle partition 3: Located between the outer plate 1 and the inner plate 2, it mainly separates the thermal insulation material 5 and the composite phase change material 6. Secondly, the middle partition 3 connects multiple fractal structure webs 4 into a whole. Part of the heat in the upper part of the fractal structure web 4 is transmitted to the composite phase change material and the inner plate 1 through the branch structure, and the other part is transmitted to the middle partition 3, and the middle partition 3 is then transmitted to the composite phase change material 6.

[0027] Inner panel 2: Located in the innermost layer of the entire thermal protection system, it is in direct contact with the internal environment of the aircraft and mainly separates the composite phase change material from the internal environment.

[0028] Thermal insulation material 5: located between the outer panel 1 and the middle partition 3, its main function is to prevent the heat on the outer panel 1 from being transferred to the interior of the aircraft.

[0029] Composite phase change material 6: close to the inner plate 2, located between the middle partition 3 and the inner plate 2, with a thermal conductivity of 2.31 W·m -1 ·K -1 The composite phase-change material 6 is composed of 75-95 wt% paraffin wax, 5 wt% expanded graphite, and 0-20 wt% of a modified low-melting-point metal-based alloy. The paraffin wax has a phase transition temperature of 42°C and a latent heat of 207.1 J / g. The expanded graphite has a purity of ≥99%. The modified low-melting-point metal-based alloy consists of 50 wt% bismuth (Bi), 25 wt% tin (Sn), 12.5 wt% cadmium (Cd), and 12.5 wt% chromium (Cr), with a melting point of 70°C.

[0030] The three-dimensional thermal conductive grid constructed by expanded graphite and low-melting-point metal-based alloy can quickly transfer local heat to the phase change material, and paraffin and low-melting-point metal-based alloy will use their own latent heat to absorb and store the incoming heat.

[0031] Through the above design, when the aircraft is flying at high speed, the heat load generated by the intense friction between the skin surface and the air is concentrated entirely on the outer plate 1. At this time, some of the heat is returned to the outside world in the form of thermal radiation, while the remaining heat is transferred to the fractal structure web 4 and the thermal insulation material 5. The fractal structure web 4 adopts a branched corrugated plate structure, connecting the outer plate 1, the middle partition 3 and the inner plate 2, and mainly plays a load-bearing role. The thermal insulation material is aerogel with a density of 220kg / m 3 , with a specific heat capacity of 500 J / kg·K and a thermal conductivity of 0.02 W / m·K. It is in direct contact with the outer plate 1 and has extremely low thermal conductivity, which can effectively prevent heat from being further transferred inward. Since the thermal conductivity of the fractal structure web 4 is much higher than that of the thermal insulation material 5, the heat transferred from the outer plate 1 is mainly transferred to the interior through the fractal structure web 4. Part of the heat transferred to the interior continues to transfer downward along the branch structure of the fractal structure web, and is then absorbed by the composite phase change material. At the same time, another part of the heat transferred to the interior is transferred to the middle partition 3, and then absorbed by the composite phase change material. The middle partition 3 is located between the thermal insulation material 5 and the composite phase change material 6. Its main function is to isolate the thermal insulation material 5 and the composite phase change material 6. Secondly, it can also further transfer the heat transferred from the fractal structure web 4 to the composite phase change material 6.

[0032] During heat transfer, the three-dimensional heat-conducting grid composed of expanded graphite and a modified low-melting-point metal-based alloy within the composite phase-change material 6 rapidly diffuses heat from the fractal structure's web 4 and intermediate partition 3 to the surrounding area, while also transferring localized heat into the composite phase-change material for absorption. The composite phase-change material is composed of a modified low-melting-point metal-based alloy (LMA), expanded graphite (EG), and paraffin wax (PA). At low temperatures, the paraffin wax undergoes a phase change, storing the incoming heat using its own latent heat. At medium to high temperatures, the low-melting-point metal-based alloy undergoes a phase change, absorbing a significant amount of latent heat. This significantly reduces the temperature of the inner panel 2 and maintains good temperature uniformity throughout the thermal protection system. Consequently, the temperature of the inner panel 2 can be maintained near the phase change temperature of the composite phase-change material 6 for extended periods, ensuring that the ambient temperature within the aircraft remains within a suitable temperature range.

[0033] In summary, the present invention effectively solves the thermal short-circuit problem existing in the traditional corrugated plate integrated thermal protection system, improves the thermal protection performance and temperature uniformity, and provides reliable protection for the safe flight of aircraft in an environment with severe aerodynamic heating.

[0034] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A fractal structure-functional integrated thermal protection system containing composite phase change materials, characterized by: The invention comprises an outer plate (1) and an inner plate (2), wherein a fractal structure web (4) is fixedly provided on the inner side of the outer plate (1), and the inner plate (2) is fixedly provided on the lower side of the fractal structure web (4), and an intermediate partition (3) is fixedly provided on the fractal structure web (4) between the outer plate (1) and the inner plate (2), and the cavity between the intermediate partition (3) and the outer plate (1) is filled with a heat insulating material (5), and the cavity between the intermediate partition (3) and the inner plate (2) is filled with a composite phase change material (6).

2. The fractal structure-functional integrated thermal protection system containing composite phase change materials according to claim 1, characterized in that: The outer plate (1), the middle partition plate (3) and the inner plate (2) are arranged parallel to each other and supported and fixed by the fractal structure web (4).

3. The fractal structure-functional integrated thermal protection system containing composite phase change materials according to claim 1, characterized in that: The fractal structure webs (4) are distributed in a leaf vein shape from outside to inside, and adjacent fractal structure webs (4) are parallel to each other. The fractal structure webs (4) are branched corrugated plate structures.

4. The fractal structure-functional integrated thermal protection system containing composite phase change materials according to claim 1, characterized in that: The outer plate (1), inner plate (2), fractal structure web (4) and middle partition (3) are all made of silicon carbide or high-temperature alloy and are integrally formed using 3D printing.

5. The fractal structure-functional integrated thermal protection system containing composite phase change materials according to claim 1, characterized in that: The thermal insulation material (5) is aerogel with a density of 220 kg / m 3 , specific heat capacity is 500 J / kg·K, and thermal conductivity is 0.02 W / m·K.

6. The fractal structure-functional integrated thermal protection system containing composite phase change materials according to claim 1, characterized in that: The thermal conductivity of the composite phase change material (6) is 2.31 W·m -1 ·K -1 , latent heat 152.1-207.2kJ / kg, leakage rate <7%.

7. The fractal structure-functional integrated thermal protection system containing composite phase change materials according to claim 1, characterized in that: The composite phase change material (6) is composed of 75-95 wt% of paraffin wax, 5 wt% of expanded graphite and 0-20 wt% of modified low melting point metal-based alloy.

8. The fractal structure-functional integrated thermal protection system containing composite phase change materials according to claim 7, characterized in that: The paraffin wax has a phase transition temperature of 42°C and a latent heat of 207.1 J / g; the expanded graphite has a purity of ≥99%; the modified low-melting-point metal-based alloy consists of 50wt% bismuth, 25wt% tin, 12.5wt% cadmium and 12.5wt% chromium, and has a melting point of 70°C.

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