A spherical graphite heater

Abstract

The present invention discloses a spherical graphite heater, which includes a graphite heating element group, a spherical water-cooled reflector, water-cooled electrodes, ceramic insulating rings, fixing nuts and molybdenum screws; the ceramic insulating rings are installed on the spherical water-cooled reflector, the water-cooled electrodes are installed on the ceramic insulating rings and pass through the water-cooled reflector, and the ceramic rings and the water-cooled electrodes are fixed by the fixing nuts; the graphite heating element group is installed on the water-cooled copper electrodes through molybdenum screws. The graphite heating elements can be assembled into a spherical shape. The shape of the first type at the top is a regular hexagon, and the second type isosceles trapezoid and the third type pentagon constitute the middle area. The solution of the present invention adopts a layout of spherical graphite heating elements with higher fitting degree and more uniform heat flux density, and has strong adjustment ability for different test pieces. For test pieces with lower temperature requirements, graphite heating elements with larger cross-sections and smaller total resistance are replaced to reduce the input power; for test pieces with higher temperature requirements, graphite heating elements with smaller cross-sections and larger total resistance are replaced to increase the input power.

Description

Technical Field

[0001] The present invention belongs to the field of ground structure thermal tests of aircraft, and particularly relates to a spherical graphite heater. Background Art

[0002] In the ground structure thermal tests of aircraft, there are mainly two radiation heating methods: quartz lamp tube radiation heating and graphite radiation heating. The quartz lamp tube heating has been applied earlier, but as a heating element, its heating temperature does not exceed 1300 °C. The graphite heater has a stronger heating capacity, and the heating temperature can reach above 2000 °C.

[0003] With the development of hypersonic aircraft, the nose cone temperature of the aircraft is as high as above 2000 °C. The graphite heater can meet the test requirements and thus has a better application prospect.

[0004] Generally, the graphite heater is formed by arranging multiple strip-shaped elements side by side, which can be assembled into a plane or a cylindrical surface, and it cannot well meet the heating requirements of the spherical nose cone of the aircraft. The existing spherical graphite heater is the graphite heater for the nose cone cover of the NASA orbiter. The NASA spherical graphite heater uses triangular graphite heating elements, which mainly have three problems: First, the heat generation at the apex angle of the triangular graphite heating element is low, and after multiple elements are spliced together, a larger lower-density heat radiation area is generated at the corner-to-corner, resulting in uneven heat radiation. Second, when the triangular elements are spliced into a spherical surface, the number of elements is large, resulting in the need for more electrodes and graphite heating elements, and it is troublesome to replace. Third, its spherical radius is large and the curvature is small, which is mostly used for the thermal test of space return vehicles, and the fitting degree to the nose cone arc surface of hypersonic aircraft is low. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems that there is no spherical graphite heater for the nose cone of hypersonic aircraft in domestic ground thermal tests, the heat flux density of the NASA triangular graphite heater is uneven, and the arc surface is too large, and to provide a spherical graphite heater composed of polygons. The theoretical heating temperature of the graphite heater of the present invention is as high as 2000 °C to 2600 °C, and the radiant heat flux density is as high as 1 to 2.5 MW / m2, which can meet the experimental conditions for the nose cone heating of hypersonic aircraft.

[0006] The present invention is realized as follows: A spherical graphite heater includes a graphite heating element group, a spherical water-cooled reflector, a water-cooled electrode, a ceramic insulating ring, a fixing nut, and a molybdenum screw; the ceramic insulating ring is installed on the spherical water-cooled reflector, the water-cooled electrode is installed on the ceramic insulating ring and passes through the water-cooled reflector, and the ceramic ring and the water-cooled electrode are fixed by the fixing nut; the graphite heating element group is installed on the water-cooled copper electrode through the molybdenum screw.

[0007] As described above, the graphite heating element group consists of three models, and the graphite heating elements can be assembled into a spherical surface; mounting holes are drilled at both ends of a single graphite heating element and are installed on the water-cooled electrodes through molybdenum screws. Each graphite heating element has a pair of water-cooled electrodes.

[0008] As described above, a water-cooled flow channel is provided in the middle of the spherical water-cooled reflector, and the heat received by the reflector is carried away by circulating cooling water.

[0009] As described above, the surface of the water-cooled plate reflector is polished to improve the reflectivity of the water-cooled reflector.

[0010] As described above, there are three models of graphite heating elements, which together form a hemispherical surface. The graphite heating elements in Area 1 at the top of the spherical surface are of Model 1, with a regular hexagon shape and a quantity of one; the graphite heating elements in Area 2 in the middle are of Model 2, with an isosceles trapezoid shape and a quantity of 18; the graphite heating elements in Area 3 that fill the pentagonal vacant area are of Model 3, with a pentagon shape and a quantity of 6. A total of 25 graphite heating elements together form the spherical surface. Except for the top being of Model 1, the others are all spliced by Model 2 and Model 3, and the number of splicing layers is determined according to the test requirements of the test elements. The heating surface spliced by the 25 graphite heating elements has three layers except for the top, mainly at the front nose cone part.

[0011] The main beneficial effects of the present invention: For the front nose cone part of a hypersonic vehicle, a layout of spherical graphite heating elements with a higher fitting degree and a more uniform heat flux density is adopted. The spherical reflector and the layout of the spherical elements have a concentrating effect on the radiant heat flux, greatly increasing the test temperature of the vehicle nose cone. Through the concentration of the spherical focal point, it is expected to achieve a doubling effect compared to a planar heater.

[0012] This spherical graphite heater has strong adjustment ability for different specimens. According to the test temperature of the specimen, the cross-sectional area of the graphite heating element can be adjusted to adjust the input power. For specimens with lower temperature requirements, replace the graphite heating element with a larger cross-section and a smaller total resistance to reduce the input power; for specimens with higher temperature requirements, replace the graphite heating element with a smaller cross-section and a larger total resistance to increase the input power.

[0013] According to the specific shape of the vehicle nose cone, the graphite heater can adjust the arc surface to a certain extent to make the heating surface better fit the arc surface of the vehicle nose cone. Description of the Drawings

[0014] Figure 1 is a schematic structural diagram of a spherical graphite heater of the present invention;

[0015] Figure 2 is a cross-sectional view of a spherical graphite heater of the present invention;

[0016] Figure 3 is the front view of a spherical graphite heater of the present invention;

[0017] Figure 4 is the front view of the first type of graphite heating element of a spherical graphite heater of the present invention;

[0018] Figure 5 is the front view of the second type of graphite heating element of a spherical graphite heater of the present invention;

[0019] Figure 6 is the front view of the third type of graphite heating element of a spherical graphite heater of the present invention;

[0020] Figure 7 is the cross-sectional view of the schematic diagram of the structure of a single graphite heating element of a spherical graphite heater of the present invention;

[0021] Figure 8 is the cross-sectional view of the optimized solution of the ceramic insulating ring of a spherical graphite heater of the present invention;

[0022] Figure 9 is the schematic diagram of the size replacement of the graphite heating element of a spherical graphite heater of the present invention.

[0023] In the figure: 1. Graphite heating element group, 101. First type of graphite heating element, 102. Second type of graphite heating element, 103. Third type of graphite heating element, 2. Water-cooled reflector, 3. Water-cooled electrode, 4. Ceramic insulating ring, 5. Molybdenum screw, 6. Aircraft nose cone test piece. Detailed implementation manners

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] As shown in Figure 1 、 Figure 2 and Figure 3 a spherical graphite heater includes a graphite heating element group 1, a spherical water-cooled reflector 2, a water-cooled electrode 3, a ceramic insulating ring 4, a molybdenum screw 5, and an aircraft nose cone test piece 6.

[0026] Among them, the graphite heating element group 1 is composed of three types of graphite heating elements, namely, the first type of graphite heating element 101, the second type of graphite heating element 102, and the third type of graphite heating element 103, which are assembled into the spherical part of the front nose cone.

[0027] The splicing method of the above-mentioned spherical surface is as follows: One graphite heating element model 101 is placed at the center, and six graphite heating elements model 102 are arranged around the six sides of the graphite heating element model 101 at a certain angle. The two adjacent sides of the adjacent graphite heating elements are parallel, forming the second layer; Then take six graphite heating elements model 102 that are opposite and parallel to the six long sides of the second layer, and form a certain angle with each graphite heating element in the second layer, forming the third layer; Then take six graphite heating elements model 102 that are opposite and parallel to the six short sides of the third layer, and form a certain angle with each graphite heating element in the third layer, forming the fourth layer; Finally, insert six graphite heating elements model 103 into the gaps between the graphite heating elements model 102 in the third and fourth layers to form a spherical surface as a whole.

[0028] The diameter of the spherical surface formed as described above is between 700 mm and 1000 mm. This diameter range can meet the heating requirements of most hypersonic vehicle nose cones. Its theoretical input power reaches 3.4 MW to 7 MW, and the empirical value of the effective heating power reaches 1.7 MW to 4.9 MW, meeting the experimental requirements of 1 MW / m2 to 2.5 MW / m2 for the nose cone specimens of the aircraft within the heating range.

[0029] The above-mentioned angle is calculated from the radius of the formed spherical surface and the size of the graphite element. The recommended empirical value is 12.5° to 25°. When it is lower than 12.5°, there are obviously too many layers of graphite elements and too many elements; when it is higher than 25°, there is an obvious problem of low spherical fitting degree. Generally, the area of a single graphite element has a limited range. When the spherical radius is small, the relative size of a single graphite element is large, and the angle degree is appropriately taken to the upper limit; on the contrary, when the spherical radius is large, the relative size of a single graphite element is small, and the angle degree is appropriately taken to the lower limit.

[0030] The above-mentioned graphite heating elements are formed by turning. The type of graphite material does not affect the technical effect of the present invention, and whether there is a thickened boss at the installation hole of each graphite heating element does not affect the technical effect of the present invention.

[0031] As Figure 1 、 Figure 2 and Figure 3 shown, the water-cooled reflector 2 is spherical as a whole, and the inner surface is a reflecting surface. Through holes are opened on the water-cooled reflector, and insulating ceramic rings 4 are installed on the through holes. The water-cooled electrodes 3 pass through and are installed on the insulating ceramic rings 4. There is a water-cooling flow channel in the middle of the water-cooled reflector, and the water-cooling flow channel and the holes do not interfere with each other.

[0032] The above-mentioned water-cooled reflector is made into a spherical surface by stamping process in this embodiment, and sealed through holes are welded after positioning and punching; it can also be made by milling a cooling flow channel on a whole spherical panel, welding a cover plate to seal the flow channel, and drilling through holes; or by using integral forming technologies such as casting and 3D printing. The water-cooled reflectors with different forming processes have the same technical effect in the present invention.

[0033] The above-described positioning and punching method in this embodiment is to manufacture a positioning and punching tooling according to the arranged graphite heating elements designed, and punch holes according to the tooling positioning.

[0034] As Figure 4 shown, the outer contour of the graphite heating element model 101 is a regular hexagon, and the regular hexagon contour size is calculated from the formed spherical surface. In this embodiment, the distance from one side of the hexagon to the center is the spherical radius multiplied by the cosine value of the included angle between each layer.

[0035] As Figure 5 shown, the outer contour of the graphite heating element model 102 is an isosceles trapezoid, and the trapezoid contour size is calculated from the formed spherical surface. In this embodiment, the height of the trapezoid is the spherical radius multiplied by the cosine value of the included angle between each layer; the short side of the trapezoid is equal to the side of the regular hexagon contour of the above-mentioned graphite part model 101; the distance from the long side of the trapezoid to the spherical center line is the spherical radius multiplied by twice the cosine value of the included angle between each layer.

[0036] As Figure 6 shown, the outer contour of the graphite heating element model 103 is a pentagon, and the pentagon contour size is calculated from the spherical radius of the formed graphite element group assembled with the graphite heating element model 101 and the graphite heating element model 102. The graphite heating element model 103 fills the gap between the graphite heating elements model 102 in the third and fourth layers. Four of the five sides of the pentagon are equal to the waist length of the graphite heating element model 102, and one side is the distance between the bottom vertices of the graphite heating element model 102 in the fourth layer.

[0037] The specific outer contour of the three graphite heating elements forming the spherical surface described above can be obtained by three-dimensional modeling.

[0038] Each of the above-mentioned graphite heating elements has two mounting holes, and the two mounting holes are connected by a continuous S-shaped bend to form a current path. The cross-section of the graphite heating element gradually becomes thinner with the working time. Therefore, the recommended value of the cross-section thickness h of the graphite element is 8-12 mm, and the recommended value of the cross-section width d is 12-30 mm to ensure a certain working time; each graphite heating element has a rounded corner. On the one hand, it can reduce the thermal stress. On the other hand, the sharp corner has low heat generation and poor heat radiation ability. Removing the sharp corner exposes the back reflector to enhance the reflection effect of the radiation and improve the cross-section current density.

[0039] The above-mentioned heater is composed of two main radiation heating bodies: a spherical graphite element group 1 formed by three types of graphite heating elements, namely graphite heating element model one 101, graphite heating element model two 102, and graphite heating element model three 103, and a water-cooled reflector 2. Digital-aided design of the model is carried out through radiation heat transfer simulation means. The simulation results show that the radiation from the front of the graphite element group 1 to the specimen and the radiation reflected by the water-cooled reflector complement each other, and can uniformly heat the nose cone specimen of the aircraft.

[0040] As Figure 7 shown, the sectional view of the enlarged structure of a single graphite heating element installation is used to show the working principle of the graphite heater. A single graphite heating element (101, 102, or 103) is installed on two water-cooled electrodes 3 through two molybdenum screws 5. The water-cooled electrodes 3 are installed on a pair of insulating ceramic rings 4. The installation method can be high-temperature resistant adhesive, or two nuts can be used to tighten from both ends. In this embodiment, the water-cooled electrode 3 and a pair of insulating ceramic rings 4 adopt an interference fit in the static fit. After the water-cooled electrode 3 is electrified and heated, it expands thermally and is fastened together with the insulating ceramic ring 4. After the test is completed and cooled, the water-cooled electrode 3 shrinks, which is convenient for adjusting the position and replacement. A pair of insulating ceramic rings 4 are installed in the through holes on the water-cooled reflector 2 from the inside and outside of the water-cooled reflector 2, and the installation method is fixed by high-temperature resistant adhesive.

[0041] The above-mentioned water-cooled electrode 3 has a water inlet, a water outlet, and a water flow channel inside, which is used to take away the heat of the electrode. The voltage is applied to the electrode rod. The cooling water is low-ion water and does not conduct electricity.

[0042] In this embodiment, the above-mentioned water-cooled electrode 3 is formed by turning and then welded. Other forming processes such as casting, die casting, and 3D printing have the same technical effects.

[0043] In this embodiment, the above-mentioned molybdenum screw 5 is used as the material. Using other high-temperature resistant materials such as tungsten, titanium, and their alloys as screws has the same technical effects.

[0044] As Figure 8 shown, a pair of insulating ceramic rings 4 can be replaced by an insulating ceramic ring composed of a pair of ceramic outer rings 7 and a ceramic ball ring 8.

[0045] The above-mentioned ceramic ball ring 8 can rotate within the spherical surface formed by a pair of ceramic outer rings 7 and undergoes sliding friction.

[0046] The above-described insulator installation method is as follows: First, install a ceramic outer ring 7 at one end of the through hole on the water-cooled reflector 2 with an adhesive; then insert the ceramic ball ring 8 into the spherical surface in a hole-to-hole manner and cover it with another ceramic outer ring 7, and use an adhesive to install this ceramic outer ring 7 at one end of the through hole on the water-cooled reflector 2. Pass the water-cooled electrode 3 through the inner cylindrical surface of the ceramic ball ring 8 and fix it with an adhesive. The water-cooled electrode 3 and the ceramic ball ring 8 are integrated and can rotate at a 30° cone angle.

[0047] The optimized effects of the insulating ceramic ring composed of the above-described pair of ceramic outer rings 7 and ceramic ball rings 8 are as follows:

[0048] First, it reduces the difficulty of precision positioning and machining of the through holes on the water-cooled reflector 2. The through holes can be machined into through holes perpendicular to the spherical surface of the water-cooled reflector 2, and the parallelism of the installation surfaces of the two graphite heating elements of a pair of water-cooled electrodes can be achieved by adjusting the angle of the water-cooled electrode 3.

[0049] Second, when the graphite heating element generates a thermal expansion effect, the movable water-cooled electrode 3 can cooperate with the slight deformation of the graphite heating element to reduce the thermal stress generated by the graphite heating element.

[0050] As Figure 9 shown, the graphite heating element model 101 can be replaced with a graphite heating element 104 with the same outer contour, the graphite heating element model 102 can be replaced with a graphite heating element 105 with the same outer contour, and the graphite heating element model 103 can be replaced with a graphite heating element 106 with the same outer contour. For the modular graphite heating elements, the present invention can increase the resistance of each graphite heating element by replacing the graphite heating element with a smaller cross-section, so as to achieve the purpose of increasing the overall power of the graphite heater. The modular graphite heating elements can meet the test requirements of different specimens.

[0051] In this specific embodiment, there is 1 graphite heating element model 101, 18 graphite heating element models 102, and 6 graphite heating element models 103. There are a total of 25 graphite heating elements of the three models, 50 supporting water-cooled electrodes 3, 50 molybdenum screws 5, and 50 pairs of insulating ceramic rings.

[0052] The main technical features protected by the present invention are:

[0053] The spherical graphite heater structure. The water-cooled plate is spherical, and the graphite heating elements form a spherical surface, with concentrated radiation, which improves the heat flux density at the spherical focus and the additional heat flux density, and thus increases the heating temperature.

[0054] Modular adjustment ability of spherical graphite heater. By replacing graphite heating elements with smaller cross-sectional areas and similar geometric shapes, the resistance of the graphite heating elements is increased, thereby increasing the upper limit of the output power and raising the heating temperature of the graphite heater; adjusting the length of the water-cooled electrode extending into the reflector can change the overall arc shape of the graphite heating element to a certain extent and improve the fitting of the arc surface of the test piece.

Claims

1. A spherical graphite heater, characterized in that: It includes a graphite heating element group, a spherical water-cooled reflector, water-cooled electrodes, ceramic insulating rings, fixing nuts and molybdenum screws; the graphite heating element group is arranged on the concave spherical surface of the spherical water-cooled reflector, the ceramic insulating ring is installed on the spherical water-cooled reflector, the water-cooled electrode is installed on the ceramic insulating ring and passes through the water-cooled reflector, and the ceramic ring and the water-cooled electrode are fixed by the fixing nut; the graphite heating element group is assembled into a spherical surface by three types of graphite heating elements; mounting holes are drilled at both ends of a single graphite heating element and are installed on the water-cooled electrode through molybdenum screws; the graphite heating element of type one in area one forms the top of the spherical surface, with a regular hexagon shape and a quantity of one; the graphite heating element of type two in area two forms the middle area, with an isosceles trapezoid shape; the graphite heating element of type three in area three, with a pentagon shape, fills the pentagonal vacancy area; each graphite heating element has a pair of water-cooled electrodes; the splicing method of the spherical surface is that one graphite heating element of type one is placed in the center, and six graphite heating elements of type two surround the six sides of the graphite heating element of type one at a certain angle, with the two adjacent sides of adjacent graphite heating elements being parallel, forming the second layer; then six graphite heating elements of type two are taken and are parallel to the six long sides of the second layer and at a certain angle to each graphite heating element of the second layer, forming the third layer; then six graphite heating elements of type two are taken and are parallel to the six short sides of the third layer and at a certain angle to each graphite heating element of the third layer, forming the fourth layer; finally, six graphite heating elements of type three are inserted into the gaps between the graphite heating elements of type two in the third layer and the fourth layer to form the spherical surface as a whole.

2. The spherical graphite heater according to claim 1, characterized in that: A water-cooling channel is arranged in the middle of the spherical water-cooled reflector, and the heat received by the reflector is carried away by circulating cooling water; the surface of the water-cooled reflector is polished.

3. A spherical graphite heater according to claim 1, characterized in that: The diameter of the spherical surface is between 700 mm and 1000 mm, its theoretical input power reaches 3.4 MW to 7 MW, and the empirical value of the effective heating power reaches 1.7 MW to 4.9 MW.

4. A spherical graphite heater according to claim 1, characterized in that: The included angle is between 12.5° and 25°.

5. A spherical graphite heater according to claim 1, characterized in that: The whole water-cooled reflector is spherical, and the inner surface is a reflecting surface; through holes are opened on the water-cooled reflector, and insulating ceramic rings are installed on the through holes, and the water-cooled electrodes pass through and are installed on the insulating ceramic rings.

6. The spherical graphite heater according to claim 1, characterized in that: Each graphite heating element has two mounting holes, and the two mounting holes are connected by a continuous S-shaped bend to form a current path. The cross-sectional thickness value of the graphite heating element is 8 to 12 mm, the cross-sectional width value is 12 to 30 mm, and the corners of each graphite heating element are rounded.

7. A spherical graphite heater according to claim 1, characterized in that: A pair of ceramic insulating rings is replaced by a pair of ceramic outer rings and a ceramic ball ring.

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