Solar unmanned aerial vehicle equipment cabin phase change thermal control system and method

Abstract

The invention relates to the technical field of unmanned aerial vehicle thermal control, discloses a solar unmanned aerial vehicle equipment cabin phase change thermal control system and method, and aims at the dynamic process of an unmanned aerial vehicle from a ground high-temperature environment to a 20km high-altitude low-temperature environment, a high-temperature phase change material and a low-temperature phase change material are adopted to control the limit and the lower limit of the equipment temperature respectively. The high-temperature phase-change materials are arranged on the side faces of all the devices and used for absorbing device heating and environment radiant heat and stabilizing the temperature of the devices to be 70 DEG C or below; the low-temperature phase-change materials are arranged on the four side walls of the inner surface of the equipment cabin shell and used for releasing latent heat in the high-altitude low-temperature environment to prevent the equipment temperature from being lower than-30 DEG C. And through the synergistic effect of the high / low-temperature phase change materials, the temperature self-adaptive regulation and control in the whole flight cycle is realized. The problems that an unmanned aerial vehicle equipment cabin thermal control measure is large in size, heavy in weight, low in efficiency and incapable of giving consideration to heating and refrigerating at the same time are solved, thermal control cost is saved, and the overall weight of an unmanned aerial vehicle is reduced.

Description

Technical Field

[0001] This invention relates to the field of thermal control technology for unmanned aerial vehicles (UAVs), specifically to a phase change thermal control system and method for the equipment cabin of a solar-powered UAV. Background Technology

[0002] Solar-powered drones are characterized by slow climb / cruise / descent speeds and high cruising altitudes, experiencing harsh conditions such as extreme temperatures and low air pressure within their flight envelope. According to GJB1172.12, the national extreme operating temperature for a 20% time risk rate is -80℃ at an altitude of 0-20km, while the extreme temperature at 0km in hot weather is 40℃. The equipment compartment of a solar-powered drone houses various electronic devices, which require suitable ambient temperature conditions for normal operation. Therefore, the development of solar-powered drones necessitates the addition of appropriate thermal control measures to the equipment compartment. Traditional thermal control methods, including air cooling, liquid cooling, thermoelectric cooling, heat pipe cooling, and attached electric heating elements, all have limitations, such as low efficiency, large size, high cost, demanding operating conditions, and the inability to simultaneously handle both cooling and heating. Therefore, they are not the optimal choice for solar-powered drones that experience extreme temperature fluctuations. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a phase change thermal control system and method for a solar-powered unmanned aerial vehicle (UAV) equipment cabin. For the dynamic process of a UAV transitioning from a high-temperature ground environment to a low-temperature environment at an altitude of 20 km, a bipolar phase change thermal control measure using high-temperature and low-temperature phase change materials is employed to control the upper and lower limits of the equipment temperature, respectively, thereby achieving adaptive temperature regulation during the flight cycle.

[0004] To achieve the above objectives, the present invention provides the following technical solution: 1. System Structure: The system includes a rectangular shell made of carbon fiber, with an aluminum alloy substrate fixed to the bottom of the shell. Four heat-generating devices are placed on top of the aluminum alloy substrate, named as Device 1 to Device 4 in descending order of their power. The upper surfaces of the high-power heat-generating Device 1 and Device 2 are connected to fins to enhance heat dissipation.

[0005] The sides of each piece of equipment are covered with a high-temperature phase change material layer composed of high-temperature paraffin wax and aluminum foam. The four side walls of the inner surface of the equipment cabin are covered with a low-temperature phase change material layer composed of low-temperature paraffin wax and aluminum foam, and metal particles are added to the low-temperature phase change material layer to enhance thermal conductivity.

[0006] The mass of the high-temperature phase change material layer is determined by the following formula: (1) In the formula, P i-equipment i Heating power, W； h i -equipment i The corresponding safe height, m； c h —Latent heat of phase transition of high-temperature paraffin kJ / kg; v p —The drone's climb rate, m / s; m hi — equipment i The required quality of high-temperature paraffin kg; The mass of the low-temperature phase change material layer is determined by the following formula: (2) In the formula, c Al —Specific heat capacity of aluminum, ; m i -equipment i quality kg; T ci -equipment i The lowest temperature at an altitude of 20km without phase change thermal control ℃； c c —Latent heat of phase transition of low-temperature paraffin kJ / kg; m c — The required quality of low-temperature paraffin kg.

[0007] 2. Thermal control methods The thermal control method mainly includes the following steps: Step 1: Pre-design Phase. Fluent software was used to simulate the temperature data of each device at altitudes of 0km, 5km, 10km, and 20km without any thermal control measures. The temperature at 0km was set to 40℃, with atmospheric pressure at ground level, taking into account solar radiation intensity at noon; the temperature at 20km was set to -80℃, without considering solar radiation intensity. Temperature and pressure values ​​at other altitudes were calculated using the standard atmospheric temperature and pressure relationship with altitude. Solar radiation intensity was calculated based on the solar radiation intensity at the corresponding time point at the climb altitude, with a climb rate of 5m / s. Flight speeds at 0, 5, and 10km were set to 8m / s, representing normal heat generation power for each device; at 20km, flight speeds were set to 30m / s, representing low heat generation power for each device. Simulations show that under certain environmental conditions at a specific altitude, a device inside the equipment bay can automatically maintain a temperature below 70°C without any thermal control measures. This means that the UAV will no longer require cooling measures if it climbs above this altitude. Let this altitude be h0. The mass of the high-temperature phase change material layer corresponding to this device can be calculated from this altitude. Similarly, simulations can obtain the temperature of each device at an altitude of 20km. If the lowest temperature of any device is below -20°C, the mass of low-temperature phase change material required for that device can be calculated from this temperature difference. The total mass of low-temperature phase change material is obtained by adding up the masses required for all four devices. Step Two: Ground Preparation Stage. Place the aluminum alloy substrate and each heating element inside the equipment housing as required. Adhere the high-temperature phase change material layer to the sides of each element, and the low-temperature phase change material layer to the four side walls of the inner surface of the equipment housing. Secure the equipment to the aluminum alloy substrate with bolts. The third step: the climb phase. When the drone is on the ground and during the initial climb, the ambient temperature is high and the equipment has a high heat output, causing the temperature to rise rapidly. High-temperature paraffin absorbs the heat from the equipment and the cabin environment. After the temperature rises to the phase transition temperature, it liquefies, absorbing a large amount of latent heat and inhibiting the equipment temperature from rising further, thus stabilizing the equipment temperature below 70°C. Step 4: Hollow Stabilization Stage. When the drone climbs to a certain altitude, the environmental conditions allow a heat-generating device to maintain a maximum temperature below 70°C even without any thermal control measures. Therefore, in the case of phase change thermal control, the device temperature begins to decrease naturally at this point, and the high-temperature paraffin wax stops its phase change. As the drone continues to climb, the device temperature gradually decreases, accompanied by a decrease in the temperature of the high-temperature paraffin wax. When the temperature drops to the phase change temperature of the high-temperature paraffin wax, it solidifies, releasing a large amount of latent heat, which initially inhibits the continued decrease in device temperature. Step 5: High-altitude cruise phase. When the drone continues to climb to an altitude of 20km, the ambient temperature is extremely low. Assuming the drone is in a low-power cruise state at night, the air temperature inside the cabin is very likely to drop below -20℃. The low-temperature phase change material layer undergoes a phase change and solidifies, releasing latent heat to heat the air temperature inside the cabin, thereby heating the various devices and further preventing the equipment temperature from dropping. The equipment temperature is maintained above -30℃ until the sun rises or the drone enters a high-power operation state. Step Six: Cycling and Descent Phase. During the cruise, as the sun continues to rise and reaches maximum radiation intensity while the equipment operates at high power, if the temperature of any equipment rises to the phase transition temperature of high-temperature paraffin wax, the high-temperature paraffin wax will liquefy to absorb heat from the equipment, stabilizing its temperature until it naturally decreases. Returning to nightfall follows the same procedure as Step Five described above. This cycle continues until the drone completes its mission or needs maintenance and lands back on the ground. During descent, the steps are reversed from the previous steps: after descending to a safe altitude, the high-temperature paraffin wax undergoes a phase transition to absorb heat and stabilize the temperature of each piece of equipment until it reaches the ground.

[0008] This invention is primarily applied to the equipment cabins of stratospheric solar-powered unmanned aerial vehicles (UAVs) that experience extreme temperature fluctuations. By adding fins to the upper surfaces of the first and second equipment units to enhance heat dissipation, and through the synergistic effect of high- and low-temperature phase change material layers, it achieves adaptive temperature control throughout the entire flight cycle of the UAV. This overcomes the shortcomings of traditional thermal control measures applied to UAVs, effectively saving thermal control costs and reducing the overall weight of the UAV. Attached Figure Description

[0009] Figure 1 This is a front cross-sectional view of the system structure of the present invention; Figure 2 This is a top view of the system structure of the present invention when it does not contain phase change materials; Figure 3 This is a schematic diagram of the rib distribution of the high-power No. 1 device of the present invention. Detailed Implementation

[0010] This invention provides a phase change thermal control system and method for a solar-powered unmanned aerial vehicle (UAV) equipment cabin. Targeting the dynamic process of the UAV transitioning from a high-temperature environment on the ground to a low-temperature environment at an altitude of 20km, the system enhances heat dissipation by adding fins to the upper surfaces of the first and second equipment (equipment 1 and equipment 2). The system also utilizes the synergistic effect of a bipolar phase change thermal control system using high-temperature and low-temperature phase change materials to achieve adaptive temperature regulation during the flight cycle.

[0011] The system and thermal control method of this application will now be described in more detail with reference to the accompanying drawings.

[0012] 1. System Structure The system is as follows Figure 1As shown, the equipment includes a carbon fiber housing 5, an aluminum alloy substrate 6, and devices mounted on the aluminum alloy substrate 6, from left to right: Device 1, Device 4, Device 3, and Device 2. Each device's sides are covered with a high-temperature phase change material layer 7, while the four side walls of the inner surface of the equipment housing 5 are covered with a low-temperature phase change material layer 8. Figure 2 The aluminum alloy substrate 6 is fixed to the lower center of the chamber by four right-angle locators placed on the lower surface inside the equipment compartment shell 5. Each piece of equipment is bolted to the aluminum alloy substrate 6 and positioned along its centerline. The spacing between the pieces of equipment and their distance from the left and right walls of the equipment compartment shell 5 are as follows: Figure 1 As shown. The high-temperature phase change material layer 7 is bonded to each piece of equipment via high thermal conductivity silicone sheets with double-sided adhesive, and the low-temperature phase change material layer 8 is also bonded to the four side walls inside the equipment compartment shell 5 via high thermal conductivity silicone sheets with double-sided adhesive. Figure 3 As shown, the upper surfaces of the first device 1 and the second device 2 are provided with ribs to enhance heat dissipation.

[0013] Placing the two high-power heating devices separately helps to distribute heat evenly, preventing heat from concentrating near Device 1 and Device 2 and causing them to overheat. This distribution also helps to increase the temperature of the low-power Device 3 and Device 4 under high-altitude and low-temperature conditions.

[0014] The dimensions of the equipment housing 5 shown are 1000×300×300mm, and the housing thickness is 1.5mm. The dimensions of the aluminum alloy substrate 6 are 950×260×2mm. The four heating devices placed on top of the aluminum alloy substrate 6 are named Device 1 to Device 4 in descending order of their power. Their normal heating powers are 100W, 80W, 20W, and 10W, respectively, and their low heating powers are half of the normal heating powers, namely 50W, 40W, 10W, and 5W. The dimensions of Device 1 are 200×150×80mm; the dimensions of Device 2 are 250×180×40mm; the dimensions of Device 3 are 120×120×50mm; and the dimensions of Device 4 are 80×60×30mm. The housing thickness of all devices is 3mm. The ribs of device 1 are 150×2×15mm with a spacing of 5.4mm, and the length direction of the ribs is consistent with the length direction of device 1. The ribs of device 2 are 180×3×20mm with a spacing of 10mm, and the length direction of the ribs is consistent with the width direction of device 2.

[0015] The high-temperature phase change material layer 7 is encapsulated in an aluminum alloy shell, internally filled with a composite material of high-temperature paraffin wax and aluminum foam. The high-temperature paraffin wax is a mixture of alkanes with 24-28 carbon atoms, with a phase change temperature of 50-60℃ and a latent heat of phase change of not less than 200 kJ / kg. The low-temperature phase change material layer 8 is also encapsulated in an aluminum alloy shell, internally filled with a composite material of high-temperature paraffin wax and aluminum foam. The low-temperature paraffin wax is a mixture of n-decane and n-dodecane, with the phase change temperature adjusted to -20℃±2℃ by adjusting the mixing ratio. Nano-copper particles are added to enhance thermal conductivity, and the latent heat of phase change is not less than 250 kJ / kg.

[0016] The mass of the high-temperature phase change material layer 7 is determined according to formula (1).

[0017] The mass of the low-temperature phase change material layer 8 is determined according to formula (2).

[0018] 2. Thermal control methods The thermal control method mainly includes the following six steps, specifically: Step 1: Pre-design Phase. First, Fluent software is used to simulate the temperature data of each device at altitudes of 0km, 5km, 10km, and 20km without any thermal control measures. At 0km, the temperature is taken as 40℃ and the pressure as atmospheric pressure (101325 Pa), considering the solar radiation intensity at noon; at 20km, the temperature is taken as -80℃, without considering solar radiation intensity. Temperature and pressure values ​​at other altitudes are calculated according to the standard atmospheric temperature and pressure relationship with altitude. Solar radiation intensity is calculated based on the solar radiation intensity at the corresponding time of ascent to the corresponding altitude, with an ascent speed of 5m / s. Flight speeds at 0, 5, and 10km are taken as 8m / s, with each device at normal heat output; at 20km, the flight speed is taken as 30m / s, with each device at low heat output. The emissivity of each device, base plate, and carbon fiber shell is based on the measured actual emissivity.

[0019] The relationship between atmospheric pressure and altitude is as follows: (3) The relationship between atmospheric temperature and altitude is as follows: (4) Simulations reveal that at altitudes of 0, 5, and 10 km, a certain device can automatically maintain a temperature below 70°C without any thermal control measures within one of these temperature ranges. Let's assume this range is 5-10 km. Within this range, the simulation is refined in increments of 1 km to obtain a specific altitude, denoted as _____. hThis altitude means that the drone will no longer need the temperature control of the high-temperature phase change material to maintain a safe temperature if it continues to climb. The safe altitude of all four devices can be determined in this way. The mass of the high-temperature phase change material layer 7 corresponding to the device can be calculated using formula (1) based on this altitude.

[0020] Similarly, the simulation can obtain the temperature of each device at an altitude of 20km. If the lowest temperature of a device is below -20 degrees, the mass of the low-temperature phase change material layer 8 required for that device can be calculated through the temperature difference. The total mass of the low-temperature phase change material layer 8 is obtained by adding up the mass required for the four devices. The calculation formula is as shown in (2).

[0021] The volume of the encapsulation shell can be determined by determining the mass of the high and low temperature phase change materials and considering the volume expansion rate after the paraffin phase change. (5) (6) In the formula, —Density of high-temperature solid paraffin kg / m 3 ； —Volume expansion rate after high-temperature paraffin liquefaction; —Density of low-temperature liquid paraffin, kg / m3; -equipment i The corresponding package size m 3 ； —The volume of the encapsulation shell required for low-temperature paraffin. m 3 ； Step Two: Ground Preparation Stage. The aluminum alloy substrate 6 and all heating devices are then prepared according to... Figure 1 As shown, the high-temperature phase change material layer 7 is placed inside the equipment housing 5, and the low-temperature phase change material layer 8 is attached to the sides of each piece of equipment. The equipment is then attached to the four side walls of the inner surface of the equipment housing 5. The equipment is fastened to the aluminum alloy substrate 6 with bolts. The third step: the climb phase. When the drone is on the ground and during the initial climb, the high heat output of the equipment, coupled with the high temperature of the outside environment, will cause the equipment temperature to rise rapidly. At this time, the high-temperature paraffin will absorb the heat of the equipment and the air inside the cabin. After the temperature rises to the phase change temperature, it will liquefy, absorb a large amount of latent heat, inhibit the further rise of the equipment temperature, and stabilize the equipment temperature below 70°C. Step 4: Hollow Stabilization Phase. When the drone climbs to a certain altitude, the environmental conditions allow a heat-generating device to maintain a maximum temperature below 70°C even without any thermal control measures. Therefore, in cases with actual phase change thermal control, the device temperature begins to decrease naturally, and the high-temperature paraffin wax stops liquefying and absorbing heat. As the drone continues to climb, the device temperature gradually decreases, accompanied by a decrease in the temperature of the high-temperature paraffin wax. When the temperature drops to the phase change temperature of the high-temperature paraffin wax, it solidifies, releasing a large amount of latent heat, initially inhibiting the continued decrease in device temperature. When the climbing altitude reaches a point where the temperatures of all four devices have naturally decreased to the phase change temperature of the paraffin wax, the latent heat released by the high-temperature paraffin wax insulates each device. After all the high-temperature paraffin wax has solidified, as the drone climbs further and the ambient temperature continues to decrease, the temperature of each device also gradually decreases. However, for a considerable period, the device temperature remains within a safe range, and the devices can operate normally. Step 5: High-altitude cruise phase. When the drone continues to climb to an altitude of 20km, the ambient temperature is extremely low. Assuming the drone is in a low-power cruise state at night, the air temperature inside the cabin is very likely to drop below -20℃. At this time, the temperature of each device will be higher than the air temperature because it is still generating heat, but it is about to enter the dangerous temperature range. In this case, the low-temperature phase change material will undergo phase change and solidify, releasing a large amount of latent heat, heating the air temperature inside the cabin, thereby heating the various devices, further preventing the device temperature from dropping, and maintaining the device temperature above -30℃ until the sun rises or the drone enters a high-power operation state. Step Six: Cycling and Descent Phase. During the cruise, when the sun continues to rise and reaches maximum radiation intensity while the equipment operates at high power, if the temperature of any equipment rises to the phase transition temperature of high-temperature paraffin, the high-temperature paraffin will liquefy to absorb heat from the equipment and stabilize its temperature until it naturally decreases. However, according to literature, the equipment temperature cannot reach such a high level under these conditions; therefore, all equipment will remain within a safe temperature range during the daytime cruise phase. Returning to nighttime follows the same procedure as Step Five. This cycle continues until the UAV completes its mission or needs maintenance and lands to return to the ground. During descent, the steps are reversed: after descending to a safe altitude, the high-temperature paraffin undergoes a phase transition to absorb heat and stabilize the temperature of all equipment until it reaches the ground.

Claims

1. A phase change thermal control system for a solar-powered unmanned aerial vehicle (UAV) cabin, characterized in that: It includes a closed equipment compartment shell (5), an aluminum alloy base plate (6) installed at the bottom of the compartment, and four heating devices placed on the aluminum alloy base plate (6); It also includes a high-temperature phase change material layer (7) and a low-temperature phase change material layer (8); the high-temperature phase change material layer (7) is attached to the side of each heat-generating device, and its phase change temperature is 50-60℃; the low-temperature phase change material layer (8) is arranged on the four side walls of the inner surface of the equipment cabin shell (5), and its phase change temperature is -20℃±2℃; both the high-temperature phase change material layer (7) and the low-temperature phase change material layer (8) are filled in aluminum foam to enhance the uniformity of thermal conductivity; the high-temperature phase change material layer (7) is used to absorb the heat generated by the equipment and the ambient heat during the UAV's climb phase, and stabilize the equipment temperature below 70℃; the low-temperature phase change material layer (8) is used to release latent heat when the UAV is in a high-altitude low-temperature environment and is cruising at low power at night, to prevent the equipment temperature from falling below -30℃.

2. The phase change thermal control system for a solar-powered unmanned aerial vehicle (UAV) cabin according to claim 1, characterized in that: The high-temperature phase change material layer (7) is composed of high-temperature paraffin and aluminum foam. The paraffin is a mixture of alkanes with 24-28 carbon atoms and a latent heat of phase change of not less than 200 kJ / kg.

3. The phase change thermal control system for a solar-powered unmanned aerial vehicle (UAV) cabin according to claim 1, characterized in that: The low-temperature phase change material layer (8) is composed of low-temperature paraffin and aluminum foam. The low-temperature paraffin is a mixture of n-decane and n-dodecane. The phase change temperature is adjusted to -20℃±2℃ by adjusting the mixing ratio, and metal particles are added to enhance thermal conductivity.

4. The phase change thermal control system for a solar-powered unmanned aerial vehicle (UAV) cabin according to claim 1, characterized in that: The equipment compartment shell (5) is a square closed shell made of carbon fiber.

5. The phase change thermal control system for a solar-powered unmanned aerial vehicle (UAV) cabin according to claim 1, characterized in that: The aluminum alloy substrate (6) is a cuboid made of aluminum alloy; the heating device is a cuboid aluminum alloy shell with ribs connected to the upper surface of the shell.

6. The phase change thermal control system for a solar-powered unmanned aerial vehicle (UAV) cabin according to claim 1, characterized in that: The mass of the high-temperature phase change material layer (7) is determined according to the following formula: ； In the formula, P i —Heating power of device i, W; h i —The safe height corresponding to device i, in meters; c h —Latent heat of phase change of high-temperature paraffin, kJ / kg; v p —The drone's climb rate, in m / s; m hi —The mass of high-temperature paraffin required for equipment i, in kg.

7. The phase change thermal control system for a solar-powered unmanned aerial vehicle (UAV) cabin according to claim 1, characterized in that: The mass of the low-temperature phase change material layer (8) is determined according to the following formula: ； In the formula, c Al —Specific heat capacity of aluminum, ; m i —The mass of device i, in kg; T ci —The lowest temperature of device i at an altitude of 20km without phase change thermal control, in °C; c c —Latent heat of phase change of low-temperature paraffin, kJ / kg; m c —The required mass of low-temperature paraffin, in kg.

8. A phase change thermal control method for the cabin of a solar-powered unmanned aerial vehicle (UAV), characterized in that, The solar-powered unmanned aerial vehicle (UAV) equipment cabin phase change thermal control system according to any one of claims 1 to 7 includes the following steps: Step 1: Arrange a high-temperature phase change material layer (7) on the side of the heating device inside the equipment compartment shell (5), and arrange a low-temperature phase change material layer (8) on the four side wall surfaces of the inner surface of the equipment compartment shell (5). Step 2: When the UAV is on the ground and in the early stages of climbing, the ambient temperature is high and the equipment heats up. The high-temperature phase change material layer (7) absorbs heat and the temperature rises to the phase change temperature and then liquefies, absorbing a large amount of latent heat, which inhibits the rise of the equipment temperature and stabilizes the equipment temperature below 70℃. Step 3: When the drone climbs to a certain altitude, the ambient temperature at this time allows the four heat-generating devices to maintain a temperature below 70°C even without any thermal control measures. Therefore, in the case of phase change thermal control, the device temperature begins to drop naturally, and the high-temperature phase change material layer (7) stops phase change. As the drone continues to climb, the device temperature continues to drop, accompanied by a drop in the temperature of the high-temperature phase change material layer (7). When the temperature drops to the phase change temperature of the high-temperature phase change material layer (7), it solidifies and releases a large amount of latent heat, which first inhibits the continuous drop in device temperature. Step 4: When the drone continues to climb to an altitude of 20km, the ambient temperature is extremely low. Assuming that the drone is in a low-power cruise state at night, the cabin air temperature is very likely to drop below -20℃. The low-temperature phase change material layer (8) undergoes phase change solidification, releases latent heat, prevents the equipment temperature from dropping further, and keeps the equipment temperature above -30℃. Step 5: When the sun continues to rise and reaches its maximum radiation intensity during the cruise and the equipment is operating at high power, if the temperature of any equipment rises to the phase change temperature of the high-temperature phase change material layer (7), the high-temperature phase change material layer (7) will liquefy and absorb the heat of the equipment to stabilize the temperature of the equipment until the temperature of the equipment drops naturally. When returning to night, the same as step 4 above is applied. This cycle continues until the UAV completes its mission or needs to be inspected and landed back to the ground. The steps are the opposite of the above steps, that is, after descending to a certain altitude, the high-temperature phase change material layer (7) undergoes a phase change and absorbs heat to stabilize the temperature of each device until the ground.

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