A thermal protection design calculation method for an aero-engine signal control box

Abstract

The application belongs to the field of aero-engine product thermal protection design calculation, and particularly relates to a thermal protection design calculation method for an aero-engine signal control box. When carrying out product thermal insulation design, the thermal insulation material in the thermal insulation layer is laid flat on the inner surface of the product shell, the heat conduction rate of the flat wall of the product shell at different temperatures is calculated based on the thermal conductivity of the thermal insulation material; the heat dissipation layer is designed based on the heat conduction rate; the selected heat dissipation material is determined, and the heat dissipation assembly is designed; the mass of the heat dissipation material is determined according to the density and volume of the selected heat dissipation material; the total heat absorbed by the heat dissipation assembly is calculated according to the mass of the heat dissipation material; the temperature rise time of the control box is calculated according to the heat conduction rate of the thermal insulation material and the heat absorbed by the heat dissipation assembly, and the design is completed when the temperature rise time meets the design requirements. The application has the characteristics of small space, light weight, good reliability and maintainability, low cost and good use effect.

Description

Technical Field

[0001] This application belongs to the field of thermal protection design calculation for aero-engine products, and specifically relates to a thermal protection design calculation method for aero-engine signal control boxes. Background Technology

[0002] The aircraft engine signal control box, along with the ionization flame detector and its connecting cable, constitutes a flame detection system to detect the ionization flame signal in the afterburner. The signal control box converts the (24±0.75)V, (3400±200)Hz DC push-pull power supply from the controller into the 115V / 3400Hz bipolar square wave AC power required for the ionization flame detector to operate. Simultaneously, it sends a high-level signal to the controller when there is a flame in the afterburner, and outputs a low-level signal otherwise. Currently, because the operating temperature of domestic integrated circuits is generally between -55℃ and +125℃, the signal control box is limited by device constraints and cannot operate in environments above 125℃.

[0003] Existing specifications require the signal control box to operate at a long-term temperature of -55℃ to +180℃ and a short-term temperature of +215℃ (no more than 15 minutes per flight hour), with a single operation not exceeding 2 hours. The product must be a sealed structure with maximum external dimensions of 220.5mm × 123mm × 130mm and a weight not exceeding 1.5kg. Therefore, heat insulation or heat absorption design is required.

[0004] Currently, commonly used thermal insulation materials can be divided into ablation-type and non-ablation-type. Ablation-type thermal insulation materials are active heat-resistant materials that use consuming substances to block heat transfer. They are characterized by safety, reliability, good thermal insulation performance, and adaptability to changes in flow fields, but they cannot be reused repeatedly, therefore they are not suitable for signal control boxes. Non-ablation-type thermal insulation materials include: fiber-based thermal insulation materials, porous thermal insulation materials, foam thermal insulation materials, and aerogel thermal insulation materials. Heat absorption in products is mainly achieved through phase change materials storing a large amount of heat during the phase change process. Commonly used phase change materials include: water, paraffin wax, glycerin, polyethylene, and paraffin wax.

[0005] Therefore, how to more effectively provide thermal protection for the inside of the control box is a problem that needs to be solved. Summary of the Invention

[0006] To address the aforementioned issues, this application provides a thermal protection design calculation method for aircraft engine signal control boxes, thereby resolving the problem of low thermal protection efficiency in existing signal control boxes.

[0007] The technical solution of this application is: a thermal protection design calculation method for an aircraft engine signal control box, comprising:

[0008] Obtain the thermal insulation material used in the signal control box, and determine the thermal conductivity and thickness of the selected thermal insulation material;

[0009] When designing product thermal insulation, the thermal insulation material in the insulation layer is laid flat on the inner surface of the product shell. The heat conduction rate of the flat wall of the product shell at different temperatures is calculated based on the thermal conductivity of the thermal insulation material. The heat dissipation layer is designed based on the heat conduction rate.

[0010] Determine the heat capacity characteristics of various heat dissipation materials, conduct comparative analysis of different heat dissipation materials, determine the selected heat dissipation material, and design heat dissipation components; determine the mass of the heat dissipation material based on its density and volume.

[0011] The total heat absorbed by the heat dissipation component is calculated based on the mass of the heat dissipation material.

[0012] The temperature rise time inside the control box is calculated based on the thermal conductivity of the insulation material and the heat absorbed by the heat dissipation components. Once the temperature rise time meets the design requirements, the design is completed.

[0013] Preferably, the insulation materials include slabs, glass wool, polystyrene foam, polyurethane foam, aerogel, aluminum silicate fiber, perlite, vacuum insulation panels, and cork.

[0014] Preferably, the formula for calculating the thermal conductivity rate is:

[0015] Q = kA(T1-T2) / d;

[0016] Where: Q is the thermal conductivity rate (W); k is the thermal conductivity [W / (m·K)]

[0017] A is the heat transfer area (m²) 2 T1 and T2 are the temperatures (K) on both sides of the flat wall, respectively; d is the thickness of the thermally conductive material.

[0018] Preferably, for every 5°C increase in the internal temperature of the product, the amount of heat transferred is Q = heat transfer rate (W) × t, where t is the time required for the internal temperature of the product to increase by 5°C.

[0019] Preferably, the heat dissipation material includes water, glycerin, polyethylene, and paraffin.

[0020] Preferably, the formula for calculating the mass of the heat dissipation material is:

[0021] m=ρV;

[0022] Where m is mass (g); ρ is material density (g / cm3); and V is material volume (cm3).

[0023] Preferably, when paraffin wax is selected as the material, the total heat absorbed by the heat dissipation component for every 5°C increase in the internal temperature of the product is:

[0024] Q = ηCm△T;

[0025] Where: Q is the absorbed heat (J); η is the heat absorption efficiency, taken as 0.6; C is the specific heat capacity of the material; m is the mass of the material; ΔT is the temperature change after absorbing heat;

[0026] a) At temperatures below 60°C, 945g of paraffin absorbs 3855J of heat for every 5°C increase in temperature.

[0027] b) At temperatures above 60°C, 945g of paraffin absorbs 4590J of heat for every 5°C increase in temperature.

[0028] c) When the temperature of paraffin reaches 60℃, it changes from solid to liquid. During the phase change, it absorbs a large amount of heat. The phase change energy storage is 200J / g. The heat absorbed by 612g of paraffin during the phase change is 122400J.

[0029] Preferably, the formula for calculating the temperature rise time inside the control box is:

[0030] t=Q 总 / Q;

[0031] Where: t is the temperature rise time in seconds; Q 总 J represents the total heat absorbed during the temperature rise.

[0032] Q is the thermal conductivity W.

[0033] The thermal protection design calculation method for aircraft engine signal control boxes provided in this application has the following advantages:

[0034] By combining thermal insulation aerogel and phase change paraffin, the internal temperature control of the sealed product is achieved. Through calculation, analysis and experimental verification, it meets the requirement that the highest internal temperature of the product does not exceed 105℃ under the conditions of long-term -55℃ to +180℃, short-term +215℃ (no more than 15 minutes per flight hour), and a maximum single working time of no more than 2 hours, thus ensuring the normal operation of the product.

[0035] This thermal protection design features small size, light weight, good reliability and maintainability, and low cost, and performs well in use. Attached Figure Description

[0036] Figure 1 This is an example diagram of the internal thermal protection design of the signal control box in this application;

[0037] Figure 2 This is a schematic diagram of the spatial dimensions of the heat dissipation component in this application. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0039] The first aspect of this application provides a thermal protection design calculation method for an aircraft engine signal control box, which is based on the design of the signal control box.

[0040] like Figure 1 The signal control box consists of two completely independent circuits, with internal electrical components made up of two identical printed circuit boards. To accommodate a temperature difference of approximately 100°C, this paper, through analysis and experimental verification, employs a combination of thermally insulating aerogel and phase change paraffin to achieve sealed internal temperature control. When the external temperature rises, the thermally insulating aerogel first blocks external heat. After a period of time, the internal temperature begins to rise. When it reaches the phase change point of the phase change paraffin, the paraffin begins to absorb heat, maintaining the internal temperature at approximately the required level.

[0041] Example diagram of product internal structure and thermal protection design is shown below. Figure 1 As shown, the product housing is made of aluminum alloy through precision casting, and the cover plate is made of aluminum alloy through machining. The housing and cover plate are fixed by fasteners and then sealed with high-temperature sealant to ensure the product's airtightness. The interior is bonded with heat insulation material, and assembled with heat dissipation components and printed circuit board components.

[0042] Includes the following steps:

[0043] Step 1: Obtain the thermal insulation material used in the signal control box, and determine the thermal conductivity and thickness of the selected thermal insulation material.

[0044] Based on the operating temperature requirements of the signal control box (-55℃~+215℃), materials with high temperature resistance and low thermal conductivity are selected as insulation materials. Commonly used insulation materials are shown in Table 1.

[0045] Table 1. Statistics on Thermal Insulation Materials

[0046]

[0047] Based on the above statistical analysis, aerogel with a thermal conductivity of 0.015–0.02 W / (m·K) was selected as the insulation material. Calculations were performed based on the thickness of the insulation material, and a thickness of 0.02 m was ultimately determined.

[0048] Step 2: When designing the product's thermal insulation, the thermal insulation material in the insulation layer is laid flat on the inner surface of the product shell. The thermal conductivity of the insulation material is used to calculate the heat transfer rate of the flat wall of the product shell at different temperatures. The heat dissipation layer is designed based on the heat transfer rate.

[0049] Using the single-layer flat wall heat transfer calculation method, the formula for calculating the heat conduction rate is as follows:

[0050] Q = kA(T1-T2) / d;

[0051] Where: Q is the thermal conductivity rate (W); k is the thermal conductivity [W / (m·K)]

[0052] A is the heat transfer area (m²) 2 T1 and T2 are the temperatures (K) on both sides of the flat wall, respectively; d is the thickness of the thermally conductive material.

[0053] Based on the product's external dimensions drawing, the product's surface area can be calculated to be 0.1112 m². 2 The heat transfer rate (W) of the product at different temperature differences was calculated, as shown in Table 2.

[0054] Table 2 Thermal conductivity (W)

[0055]

[0056] In Table 2:

[0057] 1. Based on the material testing data, the thermal conductivity is calculated as 0.016 W / (m·K);

[0058] 2. The external temperature of the product is calculated based on long-term temperatures of 180℃ and 215℃;

[0059] 3. The initial internal temperature of the product is calculated based on 25℃;

[0060] 4. Derating design is considered during the design process. The upper limit of the internal temperature of the product is set to 85℃ in an environment of 180℃ and 105℃ in an environment of 215℃.

[0061] 5. The thermal conductivity (W) decreases as the temperature difference decreases, and the change between adjacent temperature differences is very small. Therefore, the theoretical calculation is performed with a step size of 5℃.

[0062] Table 2 shows that for every 5°C increase in the internal temperature of the product, the amount of heat conducted is Q = heat conduction rate (W) × t, where t is the time required for the internal temperature of the product to rise by 5°C. Therefore, a heat dissipation component needs to be designed to buffer the conducted heat, thereby extending the time required for the temperature to rise.

[0063] Step 3: Determine the heat capacity characteristics of various heat dissipation materials, conduct comparative analysis of different heat dissipation materials, determine the selected heat dissipation material, and design heat dissipation components; determine the mass of the heat dissipation material based on its density and volume.

[0064] The function of the heat dissipation component is to absorb heat conducted into the casing, thereby prolonging the time it takes for the temperature to rise. This function requires the heat capacity characteristics of the materials; therefore, based on the heat capacity analysis of the materials and through comparative analysis of different materials, the final material was selected. The material analysis table is shown in Table 3.

[0065] Table 3 Material Analysis Table

[0066]

[0067] Based on the above analysis, paraffin wax can be used as a heat-absorbing material inside the product, utilizing its high heat capacity and phase change energy storage to absorb the heat conducted inside the product.

[0068] Based on the product's external dimensions, after attaching a 20mm thick aerogel insulation material internally, the remaining space is used to install heat dissipation components around the printed circuit board assembly. Therefore, once the printed circuit board assembly is determined, the volume of the heat dissipation components can be determined. The dimensions of the heat dissipation components are as follows: Figure 2 As shown, the total volume is 680 cm³. The formula for calculating the mass of paraffin wax is:

[0069] m=ρV;

[0070] Where m is mass g;

[0071] ρ is the material density in g / cm³;

[0072] V represents the material volume in cm³.

[0073] The density of paraffin wax is 0.9 g / cm3, and the mass of paraffin wax is calculated to be 612g using the formula for calculating the mass of paraffin wax.

[0074] Step 4: Calculate the total heat absorbed by the heat dissipation component based on the mass of the heat dissipation material.

[0075] Based on the above calculations, the mass of the heat buffer material paraffin is 612g. The total heat absorbed by the paraffin material for every 5°C increase is calculated using the following formula.

[0076] Q = ηCm△T;

[0077] in:

[0078] Q represents the heat absorbed, in J.

[0079] η is the heat absorption efficiency, taken as 0.6.

[0080] C represents the specific heat capacity of the material. The melting temperature of paraffin is calculated based on 60℃. Below 60℃, the specific heat capacity is calculated as 2.1 J / (g·K), and above 60℃, the specific heat capacity is calculated as 2.5 J / (g·K).

[0081] m is the mass of the material;

[0082] △T represents the temperature change after absorbing heat.

[0083] We can calculate using formula (3):

[0084] a) At temperatures below 60°C, 945g of paraffin absorbs 3855J of heat for every 5°C increase in temperature.

[0085] b) At temperatures above 60°C, 945g of paraffin absorbs 4590J of heat for every 5°C increase in temperature.

[0086] c) When the temperature of paraffin reaches 60℃, it changes from solid to liquid. During the phase change, it absorbs a large amount of heat. The phase change energy storage is 200J / g. The heat absorbed by 612g of paraffin during the phase change is 122400J.

[0087] Step 5: Calculate the temperature rise time inside the control box based on the thermal conductivity of the insulation material and the heat absorbed by the heat dissipation components. Once the temperature rise time meets the design requirements, the design is complete.

[0088] Table 2 shows the heat conduction rate and the total heat absorbed during the entire specified temperature rise process. The temperature rise time can be calculated using the following formula:

[0089] t=Q 总 / Q;

[0090] in:

[0091] t is the temperature rise time in seconds;

[0092] Q is the total heat absorbed during the temperature rise, in J.

[0093] Q is the thermal conductivity W.

[0094] The time required for each temperature rise period is shown in Table 4.

[0095] Table 4 Temperature rise time

[0096]

[0097] Based on the calculation and analysis in Table 4, the product can operate continuously for up to 259 minutes in an environment of 180℃, with the highest internal temperature not exceeding 85℃; when the external temperature rises to 215℃, the product can operate continuously for up to 39 minutes, with the highest internal temperature not exceeding 105℃, meeting the technical requirements of the engine for long-term operation at -55℃ to +180℃, short-term operation at +215℃ (not exceeding 15 minutes per flight hour), and a maximum single operating time of no more than 2 hours.

[0098] In a specific example, according to the calculation and analysis in Table 3, the product transfers and absorbs 186105J of external heat during operation. The product also generates a certain amount of heat during the power-on process, which is calculated according to the following formula.

[0099] Q 自 =ηUIt;

[0100] in:

[0101] η is the heating efficiency, calculated at 30%;

[0102] U represents the product's input voltage, which is set to 24V.

[0103] I represents the input current when the product is operating, which is set to 0.06A.

[0104] t represents the working time, which is calculated to be 17905s from Table 4.

[0105] Based on the above calculation, the heat generated by the circuit itself during operation is approximately 7734J, which is about 4.1% of the total external heat absorbed. Therefore, it can be ignored in theoretical calculations.

[0106] In summary, this application has the following advantages:

[0107] By combining thermal insulation aerogel and phase change paraffin, the internal temperature control of the sealed product is achieved. Through calculation, analysis and experimental verification, it meets the requirement that the highest internal temperature of the product does not exceed 105℃ under the conditions of long-term -55℃ to +180℃, short-term +215℃ (no more than 15 minutes per flight hour), and a maximum single working time of no more than 2 hours, thus ensuring the normal operation of the product.

[0108] This thermal protection design features small size, light weight, good reliability and maintainability, and low cost, and performs well in use.

[0109] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A thermal protection design calculation method for an aircraft engine signal control box, characterized in that, include: Obtain the thermal insulation material used in the signal control box, and determine the thermal conductivity and thickness of the selected thermal insulation material; When designing product thermal insulation, the thermal insulation material in the insulation layer is laid flat on the inner surface of the product shell. The heat conduction rate of the flat wall of the product shell at different temperatures is calculated based on the thermal conductivity of the thermal insulation material. The heat dissipation layer is designed based on the heat conduction rate. Determine the heat capacity characteristics of various heat dissipation materials, conduct comparative analysis of different heat dissipation materials, determine the selected heat dissipation material, and design heat dissipation components; determine the mass of the heat dissipation material based on its density and volume. The total heat absorbed by the heat dissipation component is calculated based on the mass of the heat dissipation material. The temperature rise time inside the control box is calculated based on the thermal conductivity of the insulation material and the heat absorbed by the heat dissipation components. Once the temperature rise time meets the design requirements, the design is completed.

2. The thermal protection design calculation method for an aircraft engine signal control box as described in claim 1, characterized in that, Thermal insulation materials include sintered stone, glass wool, polystyrene foam, polyurethane foam, aerogel, aluminum silicate fiber, perlite, vacuum insulation panels, and cork.

3. The thermal protection design calculation method for an aircraft engine signal control box as described in claim 1, characterized in that, The formula for calculating the thermal conductivity rate is: Q = kA(T1-T2) / d; Where: Q is the thermal conductivity (W); k is the thermal conductivity [W / (m·k)]; A is the heat transfer area (m²) 2 T1 and T2 are the temperatures (K) on both sides of the flat wall, respectively; d is the thickness of the thermally conductive material.

4. The thermal protection design calculation method for an aircraft engine signal control box as described in claim 3, characterized in that, For every 5°C increase in the internal temperature of the product, the amount of heat transferred is Q = heat transfer rate (W) × t, where t is the time required for the internal temperature of the product to increase by 5°C.

5. The thermal protection design calculation method for an aircraft engine signal control box as described in claim 1, characterized in that, The heat dissipation material includes water, glycerin, polyethylene, and paraffin.

6. The thermal protection design calculation method for an aircraft engine signal control box as described in claim 5, characterized in that, The formula for calculating the mass of heat dissipation material is: m=ρV; Where m is mass (g); ρ is material density (g / cm3); and V is material volume (cm3).

7. The thermal protection design calculation method for an aircraft engine signal control box as described in claim 5, characterized in that, When paraffin wax is selected as the material, the total heat absorbed by the heat dissipation components for every 5°C increase in the internal temperature of the product is: Q = ηCm△T; Where: Q is the absorbed heat (J); η is the heat absorption efficiency, taken as 0.6; C is the specific heat capacity of the material; m is the mass of the material; ΔT is the temperature change after absorbing heat; a) At temperatures below 60°C, 945g of paraffin absorbs 3855J of heat for every 5°C increase in temperature. b) At temperatures above 60°C, 945g of paraffin absorbs 4590J of heat for every 5°C increase in temperature. c) When the temperature of paraffin reaches 60℃, it changes from solid to liquid. During the phase change, it absorbs a large amount of heat. The phase change energy storage is 200J / g. The heat absorbed by 612g of paraffin during the phase change is 122400J.

8. The thermal protection design calculation method for an aircraft engine signal control box as described in claim 5, characterized in that, The formula for calculating the temperature rise time inside the control box is: t=Q 总 / Q; Where: t is the temperature rise time in seconds; Q 总 J represents the total heat absorbed during the temperature rise. Q is the thermal conductivity W.

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