All-weather bidirectional cold and heat energy collecting device imitating ginkgo leaf structure and application of all-weather bidirectional cold and heat energy collecting device

Abstract

The invention discloses an all-weather two-way cold and heat trapping device based on a ginkgo leaf bionic structure and application of the all-weather two-way cold and heat trapping device. The device comprises a spectrum selective aerogel layer, an air spacing layer, a composite heat storage layer loaded with a phase change material, and a heat preservation shell composed of a high-reflection inner wall and a low-heat-conductivity material from top to bottom. In the daytime, solar radiation efficiently penetrates through the aerogel, and the heat storage layer is driven to absorb and store heat energy; the high-reflection inner wall and the low heat conductivity of the aerogel synergistically inhibit heat loss, the actually measured highest heat storage temperature reaches 381K, and the photo-thermal storage efficiency reaches 87.5%; and the efficiency is still kept at 77.1% at the wind speed of 2m. S <-1 >. At night, the aerogel radiates and dissipates heat to the deep space of the universe by utilizing high infrared emissivity, so that passive refrigeration is realized, and the maximum cooling power reaches 118.8 W.m <-2 >. Theoretically, the maximum annual energy-saving potential reaches 5321.4 MJ.m <-2 > and is improved by 45% and 223% compared with a one-way solar heat collecting system and a pure radiation refrigerating system.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of all-weather cold and hot energy two-way trapping device based on plant bionics and its application, especially to a kind of light-thermal storage-radiation refrigeration integrated device imitating ginkgo biloba leaf structure and its application, which is suitable for thermoelectric conversion, building energy saving and off-grid regional energy supply system, belongs to renewable energy utilization technical field. BACKGROUND

[0002] More than 50% of global terminal energy consumption is used for heating and cooling, resulting in annual carbon emissions of up to 37.8 billion tons. Solar thermal conversion and radiation refrigeration technology can efficiently capture solar radiation heat and cosmic deep space cold energy, providing an important path for achieving zero-carbon energy supply. However, solar thermal collection systems are significantly affected by day-night alternation and seasonal changes, with an annual effective operation time of less than 45%; the performance of radiation refrigeration is easily disturbed by cloud cover and atmospheric humidity, limiting its continuous and stable operation.

[0003] Phase change materials (PCMs) have great potential in the temporal and spatial regulation of thermal energy due to their high energy storage density and nearly constant phase change temperature. Integrating PCMs with solar thermal conversion or radiation refrigeration technology not only simplifies the heat transfer process but also effectively reduces efficiency losses in energy conversion. However, most current systems struggle to achieve all-weather energy capture, particularly in the transition between day and night modes. For example, to improve daytime solar absorption efficiency, PCMs are often coated with a black coating that has high solar absorption and low mid-infrared emission. While this design is beneficial for daytime heat collection, it cannot effectively radiate heat at night due to weak mid-infrared emission, making it difficult to utilize the sky as a cold source. Conversely, devices suitable for night-time radiation refrigeration typically have high infrared emission, but their performance decreases during the day due to excessive solar absorption or heat loss, making it difficult to balance daytime functionality.

[0004] In recent years, although solar thermal utilization and sky radiation refrigeration technology have made progress in capturing thermal and cold energy, respectively, they are often operated independently and lack coordination mechanisms. While some research has attempted to use phase change materials for thermal buffering and regulation, their potential in all-weather energy capture, particularly in the design of systems that can simultaneously collect solar heat and cool at night, has not been fully explored. Therefore, developing an integrated energy capture system that can continuously operate day and night and efficiently capture solar thermal energy and cosmic cold energy is crucial for advancing sustainable thermal management technology. Through the coordinated optimization of material design and system architecture, continuous and stable acquisition of environmental energy can not only improve energy utilization efficiency but also provide a reliable energy source for thermoelectric conversion, building energy saving, and other applications. SUMMARY

[0005] Invention purposes: In view of the problems of the prior art that solar heat conversion and radiation refrigeration are difficult to work together, energy collection mode is single, and continuous energy supply ability is insufficient day and night, one purpose of the present application is to provide a full-weather bidirectional cold and heat energy collection device simulating ginkgo leaf structure. Another purpose of the present application is to provide a full-weather thermoelectric power generation system based on bidirectional cold and heat energy capture, which comprises the full-weather bidirectional cold and heat energy collection device. The collection device realizes the unity of daytime efficient heat absorption and night passive refrigeration by coupling the spectrum selective regulation layer and the composite heat storage layer, breaks through the technical barrier that the traditional system cannot simultaneously consider photothermal utilization and radiation cooling in function, and provides an innovative solution for realizing full-weather and sustainable energy management.

[0006] Technical scheme: The full-weather bidirectional cold and heat energy collection device simulating ginkgo leaf structure comprises a spectrum selective aerogel layer and a composite heat storage layer loaded with phase change material arranged in sequence from top to bottom, and an air gap is arranged between the spectrum selective aerogel layer and the composite heat storage layer as an air spacing layer; the overall structure formed by the spectrum selective aerogel layer and the composite heat storage layer is wrapped with a heat preservation shell on the outside; the spectrum selective aerogel layer is fixed on the top inner side of the heat preservation shell through interference fit, and the composite heat storage layer is detachably installed in the interior of the heat preservation shell.

[0007] Further, the spectrum selective aerogel layer simulates the leaf epidermis wax layer, has high solar light transmittance and high mid-infrared emissivity, the thickness of the spectrum selective aerogel layer is 5-8 mm, and the spectrum selective aerogel layer has excellent optical regulation and control capability. The transmittance in the solar spectrum band of 0.25-2.5 μm is more than 85%, and the emissivity in the mid-infrared atmospheric window band of 8-13 μm is more than 95%.

[0008] Further, the composite heat storage layer loaded with phase change material simulates the leaf tissue structure and is used for realizing heat storage and release, and the thermal conductivity of the composite heat storage layer is 20 W·m -1 ·K -1 The above can be composed of a metal skeleton or a ceramic skeleton loaded with phase change material, and the thickness is 3-5 mm. The configuration of the composite heat storage layer is dynamically switched according to the solar radiation intensity, when the solar irradiance is higher than or equal to 50 W·m -2 , the composite heat storage layer loaded with the first phase change material is enabled; and when the irradiance is lower than 50 W·m -2When the ambient temperature is higher than the phase change temperature of the first phase change material, the device switches to the second phase change material to adapt to the all-weather operation requirement. The phase change temperature of the first phase change material is higher than the average daytime ambient temperature, and the second phase change material is lower than the average nighttime ambient temperature. The phase change temperature of the phase change material is preferably in the range of 280-420K. Preferably, the first phase change material is selected from the sliced paraffin wax (52-54℃, Shanghai Test, phase change temperature 325K, phase change latent heat not less than 135J·g -1 ) provided by Sinoreagent Co., Ltd. or OP100E (phase change temperature 373K, phase change latent heat not less than 175J·g -1 ) provided by Hangzhou Luer Energy Technology Co., Ltd. The second phase change material is preferably OP10E (phase change temperature 283K, phase change latent heat not less than 120J·g -1 ) provided by Hangzhou Luer Energy Technology Co., Ltd. Other paraffin phase change materials with similar performance can also be selected according to actual needs. To monitor the temperature change of the heat storage layer in real time during the energy harvesting process, a thermocouple is arranged at the bottom of the heat storage layer to record the temperature response curve during the daytime heat absorption and nighttime refrigeration process.

[0009] Further, the thickness of the air spacing layer is 3-5mm. This structure is designed to prevent the phase change material (PCM) from seeping out in the molten state and directly contacting and contaminating the spectrally selective aerogel layer, thereby maintaining the high transmittance and high emissivity of the aerogel and ensuring the optical performance stability of the device in long-term cyclic operation.

[0010] Further, the thermal conductivity of the heat insulation shell is 0.05W·m -1 ·K -1 The inner wall of the heat insulation shell is provided with a high reflection layer, which can significantly inhibit the lateral and bottom heat loss of the heat storage material and improve the energy utilization efficiency. The high reflection layer can be one or more of aluminum foil, silver-coated film or high reflectivity metal coating. The heat insulation shell is made of heat insulation material, and the heat insulation shell is provided with a matching embedding groove inside the heat insulation shell. The spectrally selective aerogel layer is embedded in the groove by interference fit (such as an embedded structure), which realizes firm fixation and good thermal isolation, and facilitates modular assembly and maintenance of the device.

[0011] Further, the preparation method of the spectrally selective aerogel layer comprises the following steps:

[0012] (1) Sol preparation: mixing tetramethoxysilane, water and ethanol to promote the hydrolysis of methoxy to generate silanol to obtain a sol;

[0013] (2) Catalytic gelation: adding ammonia methanol solution to the sol to catalyze the condensation reaction to form a Si-O-Si three-dimensional network structure to obtain a gel;

[0014] (3) Hydrophobic modification and drying: the gel is immersed in a hexamethyldisilazane solution to replace the surface hydroxyl groups with -Si(CH3)3 groups, then transferred to an ethanol solution for aging at room temperature, and finally dried by CO2 supercritical drying and heat treatment.

[0015] Further, in step (1), the mass ratio of tetramethoxysilane, water and methanol is 1.0:(0.47-0.48):(1.3-1.4); in step (2), a methanol solution of ammonia with a concentration of 2.0-3.0 mol·L-1 is used as a catalyst, the volume ratio of the sol to the methanol solution of ammonia is 1:(60-65), and the condensation reaction time is 1-2 min; in step (3), the gel is immersed in a hexamethyldisilazane (HMDS) solution for more than 12 h, the aging time is more than 7 days; the CO2 supercritical drying conditions are 35℃, 5 MPa, and drying for 5-6 h; and the heat treatment is to increase the temperature to 400℃ at a rate of 0.5℃·min-1 and keep the temperature for more than 48 h. -1 -1

[0016] The device has a bidirectional energy capture function: in the daytime mode, solar radiation is transmitted through the spectrally selective aerogel layer and is absorbed and converted into heat energy by the composite heat storage layer, so that the temperature of the composite heat storage layer is significantly higher than the ambient temperature; in the nighttime mode, the aerogel layer dissipates heat to space through mid-infrared band radiation, so that the temperature of the composite heat storage layer is 4-6 K lower than the ambient temperature, achieving passive cooling and cold energy storage.

[0017] The application also provides a full-time bidirectional cold and heat energy collection device, which comprises a base, a composite heat storage layer, an aerogel layer and a heat insulation layer, wherein the base is provided with a heat insulation layer, the heat insulation layer is provided with a composite heat storage layer, and the composite heat storage layer is provided with an aerogel layer.

[0018] ​​Further, the thermoelectric conversion module adopts a thermoelectric material based on the Seebeck effect, preferably a bismuth tellurium (Bi2Te3) based thermoelectric module, for converting a thermal gradient into electrical energy. The heat dissipation structure is a high-thermal-conductivity metal heat sink, preferably a copper or aluminum heat sink, which serves as a cold-end heat sink to maintain a temperature difference with the hot end. In the daytime working mode of the system, solar radiation passes through the spectrally selective aerogel layer to heat the composite heat storage layer, making its temperature higher than the ambient temperature, forming a "hot end-cold end" thermal gradient to drive the thermoelectric module to generate electricity; in the night working mode, the spectrally selective aerogel layer dissipates heat to deep space through mid-infrared radiation (8-13 μm), making the temperature of the composite heat storage layer lower than the ambient temperature, and the composite heat storage layer becomes the cold end, the direction of heat flow is reversed, but an effective thermal gradient can still be maintained to continue generating electricity. And multiple said power generation systems can be connected in parallel or series to improve the output voltage or power. The open-circuit voltage of the system under 1 times solar irradiance intensity (1-sun) is not less than 0.15 V.

[0019] The present application is based on the bidirectional energy management mechanism of ginkgo leaves: the spectrally selective aerogel layer mimics the leaf epidermis wax layer, with high solar transmittance (daytime solar energy capture) and high mid-infrared emissivity (nighttime radiative cooling), achieving spectral selective regulation; the composite heat storage layer mimics the leaf mesophyll tissue, by loading materials with different phase change temperatures, achieving efficient storage and controllable release of thermal energy. This biomimetic design artificially replicates the dual function of "photosynthesis + radiative cooling" in nature, providing biological inspiration for all-weather energy capture. Further, by coupling the aerogel-enhanced cold and heat energy collection device with spectral selectivity and the thermoelectric conversion module, the daytime heat absorption and nighttime cooling are coordinated to operate, a continuous reversible thermal gradient is established to drive the thermoelectric module to generate electricity continuously for 24 hours, solving the problem of discontinuous heat source and unstable output of traditional thermoelectric systems.

[0020] Advantages: Compared with the prior art, the present application has the following significant advantages:

[0021] (1) Aerogel performance breakthrough: The spectrally selective aerogel layer prepared in the present application has excellent spectral frequency division characteristics, with a transmittance of 86.14% in the solar spectrum band (0.3-2.5 μm) and an emissivity of 97.7% in the mid-infrared atmospheric window (8-13 μm), achieving the synergistic optimization of high transmittance and high emissivity, solving the problem that traditional materials cannot be considered. At the same time, its thermal conductivity is as low as 0.022 W·m -1 ·K -1 , with excellent thermal insulation performance, further improving the overall thermal management efficiency of the device.

[0022] (2) Breakthrough in day and night efficiency: During daytime operation, solar radiation passes through the aerogel layer and is absorbed by the composite heat storage layer, then converted into stored heat energy. Simultaneously, the aerogel layer and the insulation shell work together to suppress heat loss through conduction, convection, and radiation. The measured solar thermal conversion efficiency reaches 87.5%, and the highest heat storage temperature reaches 381K. During nighttime operation, the spectrally selective aerogel layer dissipates heat to deep space through mid-infrared radiation, driving the phase change material to solidify and store cold energy, with a maximum cooling power of 118.8 W·m³. -2 The minimum storage temperature is 4-6K lower than the ambient temperature. The device achieves 24-hour uninterrupted energy capture, with a theoretical annual energy saving potential of up to 5321.4 MJ·m³. -2 Compared to a single solar thermal system, the operating time is extended by 100% and energy savings are increased by 45%; compared to a single radiant cooling device, energy savings are increased by 223%.

[0023] (3) Breakthrough in environmental stability: The device of this invention can operate at a wind speed of 2 m / s -1 Under convective conditions, the photothermal storage efficiency remains at 77.1%, and the heat storage time increases by only 5.2%; its temperature fluctuation coefficient is reduced by 11% compared with conventional glass-covered systems, demonstrating excellent anti-interference ability and operational stability.

[0024] (4) The system described in this invention provides continuous power generation around the clock: By capturing heat and cold energy through daytime heat absorption and nighttime cooling, a continuous thermal gradient is constructed, enabling uninterrupted power generation 24 hours a day; the aerogel layer has both high solar transmittance and high-to-medium infrared emissivity, which, combined with phase change material energy storage, significantly improves the stability of the system in complex environments such as cloudy and windy conditions. Actual test results show that at 1 times the solar irradiance (1-sun), the open-circuit voltage can reach 0.15V (ΔT is 6.9K), while at 8 times the solar irradiance, the open-circuit voltage reaches 0.80V, with a maximum output power of 120mW; the system has a compact structure, is easy to expand, and can drive small electronic devices (such as fans and sensors) through parallel connection. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the all-weather bidirectional cold and heat energy collection device with a simulated ginkgo leaf structure, as shown in Example 1.

[0026] Figure 2 This is a schematic diagram of the preparation process of the spectroselective silica aerogel in Example 1;

[0027] Figure 3 This is a schematic diagram of the energy flow of an all-weather, two-way cold and heat energy harvesting device with a biomimetic prototype and a ginkgo leaf-like structure.

[0028] Figure 4 This is a schematic diagram of the all-weather bidirectional cold and heat energy collection device with a simulated ginkgo leaf structure, as shown in Example 2.

[0029] Figure 5 This is a schematic diagram of a solar thermal conversion and storage performance testing system;

[0030] Figure 6 The thermal storage devices of Example 2 and Comparative Example 1 are at 1.0 kW·m -2 Real-time temperature change curve under illumination conditions;

[0031] Figure 7 The thermal storage device in Example 2 is tested under different solar irradiance intensities (0.3–1.5 kW·m). -2 The temperature response curves under various irradiation conditions were obtained; the results show that the device has good thermal response characteristics and energy storage capacity over a wide irradiation range.

[0032] Figure 8 The thermal storage devices at 1.0 kW·m³ have different air layer thicknesses (0 mm, 3 mm, 5 mm). -2 Real-time temperature change curve under illumination conditions;

[0033] Figure 9 These are the real-time temperature change curves at the bottom of the energy storage unit and the radiation intensity spectrum of the atmospheric window band (8–13 μm) of the device in Example 4 under clear weather conditions.

[0034] Figure 10 These are the real-time temperature change curves and radiation intensity spectra of the bottom of the composite thermal storage layer in Example 4 under cloudy weather conditions;

[0035] Figure 11 This is a schematic diagram of the all-weather thermoelectric power generation system in Example 5;

[0036] Figure 12 These are photographs of the all-weather power generation test system in Example 5;

[0037] Figure 13 The all-weather thermoelectric power generation system in Example 5 operates at 1 times the solar irradiance (1000 W·m). -2 The graph shows the changes in temperature difference ΔT and corresponding open-circuit voltage VOC over time under the following conditions:

[0038] Figure 14 This is the open-circuit voltage (VOC) output curve of the all-weather thermoelectric power generation system in Example 5 under three different solar irradiance intensities;

[0039] Figure 15 The all-weather thermoelectric power generation system in Example 5 operates under 8 times concentrated solar irradiance (8000 W·m). -2 Transient open-circuit voltage response diagram under ( );

[0040] Figure 16This is the output power diagram of the all-weather thermoelectric power generation system in Example 5 under the same conditions;

[0041] Figure 17 This is the open-circuit voltage (VOC) output curve of the power generation system over 24 hours, calculated based on outdoor temperature difference data obtained under clear weather conditions in Example 5. Detailed Implementation

[0042] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0043] Example 1

[0044] like Figure 1 As shown, the present invention provides an all-weather, bidirectional thermal energy harvesting device with a ginkgo leaf-like structure. From top to bottom, it comprises a spectrally selective aerogel layer 1 and a composite heat storage layer 2 loaded with a phase change material. An air gap 3 is provided between the aerogel layer 1 and the composite heat storage layer 2. The overall structure formed by the aerogel layer 1 and the composite heat storage layer 2 is wrapped with an insulating shell 4. The spectrally selective aerogel layer 1 is fixed to the inner top of the insulating shell 4 by an interference fit, and the composite heat storage layer 2 is detachably installed inside the insulating shell. In this embodiment, the spectrally selective aerogel layer 1 and the composite heat storage layer 2 have the same length and width and are wrapped by the insulating shell 4.

[0045] Among them, the spectrally selective aerogel layer 1 simulates the waxy layer of leaf epidermis, possessing both high solar transmittance and high-to-medium infrared emissivity. To obtain an aerogel material with both high solar transmittance and high-to-medium infrared emissivity, the spectrally selective aerogel layer 1 is prepared according to the following steps:

[0046] First, tetramethoxysilane, water, and methanol were mixed in a mass ratio of 1.0:(0.47–0.48):(1.3–1.4) to allow the methoxy group to hydrolyze and form a silanol, yielding a sol. Then, a solution with a concentration of 2.0–3.0 mol·L⁻¹ was added. -1 Ammonia in methanol solution was used as a catalyst, with a sol-to-catalyst solution volume ratio of 1:(60-65). A condensation reaction was carried out at room temperature for 1-2 minutes to form a Si–O–Si three-dimensional network structure, yielding a wet gel. The wet gel was then immersed in hexamethyldisilazane (HMDS) for at least 12 hours to replace the hydroxyl groups on the gel surface and introduce hydrophobic –Si(CH3)3 groups, obtaining a modified gel. Subsequently, the modified gel was transferred to an ethanol solution and aged at room temperature for at least 7 days. Finally, supercritical drying and heat treatment were performed sequentially. Supercritical drying was carried out at 35℃ and 5MPa using supercritical CO2 for 5-6 hours. The heat treatment process was carried out at 0.5℃·min. -1The heating rate was increased to 400℃ and held at this temperature for more than 48 hours, ultimately obtaining a spectrally selective silica aerogel layer with excellent properties. The spectrally selective aerogel layer 1 has a thickness of 5-8 mm, a transmittance of over 85% in the solar spectrum (0.25-2.5 μm), and an emissivity of over 95% in the mid-infrared atmospheric window (8-13 μm). The above preparation process is as follows: Figure 2 As shown, it covers key steps such as sol-gelation, hydrophobic modification, aging, supercritical drying and heat treatment.

[0047] The composite thermal storage layer 2, loaded with phase change material, simulates mesophyll tissue and is used to store and release thermal energy. It has a thermal conductivity of 20 W·m. -1 ·K -1 The above can be a metal or ceramic skeleton supporting the phase change material, and the thickness of the composite thermal storage layer 2 is 3-5 mm. Different composite thermal storage layers are dynamically switched according to the solar irradiance intensity: when the solar irradiance intensity is higher than or equal to 50 W·m⁻¹. -2 When the irradiation intensity is below 50 W·m, the composite thermal storage layer loaded with the first phase change material is activated; -2 When switching to the composite thermal storage layer loaded with the second phase change material, it adapts to all-weather operation requirements. The phase change temperature of the first phase change material is higher than the average daytime ambient temperature, used for absorbing and storing solar thermal energy during the day; the phase change temperature of the second phase change material is lower than the average nighttime ambient temperature, used for absorbing ambient cold energy at night, achieving cold energy storage. The phase change temperature of the phase change material is between 280-420K. To monitor the temperature change of the composite thermal storage layer 2 in real time during energy capture, thermocouples are arranged at its bottom to record its temperature response curves during daytime heat absorption and nighttime cooling. The thickness of the air gap layer 3 is 3-5mm, used to prevent the phase change material (PCM) from seeping out in the molten state and directly contacting and contaminating the spectrally selective aerogel layer 1, thereby maintaining the high transmittance and high emissivity of the aerogel and ensuring the optical performance stability of the device during long-term cyclic operation. The thermal conductivity of the insulation shell 4 is 0.05W·m. -1 ·K -1 The inner wall of the insulation shell 4 is provided with a high-reflectivity layer, which can significantly suppress lateral and bottom heat loss of the heat storage material and improve energy utilization efficiency. The insulation shell 4 is made of insulation material and has a pre-set mounting groove that matches the size of the spectrally selective aerogel layer 1. The spectrally selective aerogel layer 1 is embedded in the groove by an interference fit, achieving firm fixation and good thermal insulation, while facilitating modular assembly and maintenance of the device. The insulation material is selected from one or more of rubber and plastic materials, polyurethane foam, or aerogel felt; the high-reflectivity layer is one or more of aluminum foil, silver-plated film, or high-reflectivity metallic coating.

[0048] Example 2

[0049] Based on the all-weather bidirectional energy harvesting device described in Example 1, the natural mechanism of bidirectional energy harvesting by ginkgo leaves during the day-night cycle is simulated. Figure 3 The device demonstrates the energy transfer pathways of daytime photothermal conversion and thermal energy storage, and nighttime radiative cooling and cold energy storage, showcasing its bidirectional energy capture capability under all-weather conditions.

[0050] In this embodiment, the spectrally selective aerogel layer 1 is prepared according to the following steps:

[0051] First, tetramethoxysilane, water, and methanol were mixed in a mass ratio of 1.0:0.473:1.368 to allow the methoxy group to hydrolyze and form a silanol, yielding a sol. Then, a 2.0 mol·L⁻¹ solution was added. -1 Ammonia in methanol solution was used as a catalyst, with a sol-to-catalyst solution volume ratio of 1:63.4. A condensation reaction was carried out at room temperature for 2 minutes, forming a Si–O–Si three-dimensional network structure, resulting in a wet gel. The wet gel was then immersed in hexamethyldisilazane (HMDS) for 12 hours to replace the hydroxyl groups on the gel surface and introduce hydrophobic –Si(CH3)3 groups, obtaining a modified gel. Subsequently, the modified gel was transferred to an ethanol solution and aged at room temperature for 7 days. Finally, supercritical drying and heat treatment were performed sequentially. Supercritical drying was carried out at 35℃ and 5MPa using supercritical CO2 for 5-6 hours. The heat treatment process was carried out at 0.5℃·min. -1 The heating rate was increased to 400℃, and the temperature was maintained at this level for 48 hours, ultimately yielding a spectrally selective silica aerogel layer with excellent properties. The resulting spectrally selective aerogel layer 1 has a diameter of 26 mm and a thickness of 6 mm. The transmittance of the spectrally selective aerogel layer 1 in the 0.3-2.5 μm wavelength range is 86.14%, the emissivity in the mid-far-infrared atmospheric transparency window band (8-13 μm) is 97.7%, and the thermal conductivity is 0.022 W·m. -1 ·K -1 It combines high light transmittance, high emissivity and excellent heat insulation performance, and can achieve the dual functions of efficient light transmission during the day and efficient radiative cooling at night.

[0052] The composite thermal storage layer 2 loaded with phase change material is prepared by vacuum impregnation of paraffin (phase change temperature 325K) with a porous silicon carbide (SiC) ceramic skeleton with a diameter of 26mm and a thickness of 5mm, thus forming a composite phase change material with both high thermal conductivity and high energy storage density.

[0053] The specific preparation method of the composite thermal storage layer 2 loaded with phase change material in this embodiment is as follows:

[0054] First, sisal fiber bundles with a diameter of 100-150 μm and a length of 5 cm were taken and ultrasonically cleaned with ethanol for 30 min to remove surface impurities. Then, they were immersed in a flour suspension (flour to water mass ratio of 20:80) for 10 min. Subsequently, they were neatly arranged axially and wrapped in pre-cut gauze. The assembly was placed in a hot press, preheated at 50℃ for 10 min, and then subjected to a pressure of 15 MPa for 36 h to obtain a dense fiber preform. Next, the obtained preform was placed in a tube furnace and heated in a high-purity argon atmosphere (flow rate 50 mL / min). -1 ) at 1℃·min -1 The temperature was increased to 850℃ and held for 30 min, then naturally cooled to room temperature to obtain a porous carbon framework with a porosity of 82%. Subsequently, the porous carbon framework was mixed with silicon powder with a particle size of 5-10 μm at a mass ratio of 3.8:1. The silicon powder was coated in two layers on the outside of the porous carbon framework, and the mixture was placed in a graphite crucible. The crucible was then placed in a vacuum sintering furnace and sintered at 10℃·min. -1 The temperature was raised to 1550℃ and held for 2 hours to complete the carbothermic reduction reaction, generating a silicon carbide framework containing free silicon. To remove residual silicon, the reaction product was first heated to 1800℃ and held for 1 hour in a high-temperature furnace, then cooled to 1750℃ and held for 0.5 hours, ultimately reducing the free silicon content to below 0.5 wt%. Finally, the first phase change material—sliced ​​paraffin (52–54℃, Shanghai test, phase change temperature 325K, latent heat of phase change not less than 135 J·g) provided by Sinopharm Chemical Reagent Co., Ltd. -1 The second phase change material is OP10E (phase change temperature 283K, latent heat of phase change not less than 120J·g) provided by Hangzhou Ruhr Energy Technology Co., Ltd. -1 The pretreated silicon carbide skeletons were heated to 20°C above their melting point until completely melted and placed in a vacuum impregnation tank. The pretreated silicon carbide skeletons were then immersed in molten paraffin wax and evacuated to 10°C. -1 Pa was maintained for 24 hours to allow the phase change material to fully fill the pores of the framework. Then, it was slowly cooled to room temperature to obtain the composite thermal storage layer 2 with two types of loaded phase change materials.

[0055] The thickness of the air gap 3 is 3mm, and the thermal insulation shell 4 uses materials with a thermal conductivity of no more than 0.05W·m. -1 The K-1 high-density rubber and plastic insulation board (brand: Yimeisi, model: B2) has a silver-plated high-reflective layer on its inner wall, which can significantly suppress heat loss from the sides and bottom of the heat storage material and improve energy utilization efficiency.

[0056] Comparative Example 1

[0057] Based on Example 2, the top spectrally selective aerogel layer 1 was replaced with ordinary optical glass of the same thickness, while all other conditions remained unchanged.

[0058] Example 3

[0059] Based on Example 2, the thickness of the air spacer 3 was adjusted to 5 mm, while the other conditions remained unchanged.

[0060] Comparative Example 2

[0061] Based on Example 2, the air gap layer 3 is removed, so that the spectrally selective aerogel layer 1 is in direct contact with the composite heat storage layer 2, while the other conditions remain unchanged.

[0062] Example 4

[0063] like Figure 4 As shown, based on Example 2, the following parts are changed:

[0064] The thickness of the air gap layer 3 was adjusted to 5 mm. The composite heat storage layer 2 was prepared by vacuum impregnation of a silicon carbide ceramic skeleton with a diameter of 13 mm and a thickness of 3 mm with paraffin (OP100E) at a phase change temperature of 373 K. The spectrally selective aerogel layer 1 and the composite heat storage layer 2 were arranged opposite each other, and the composite heat storage layer 2 was surrounded by air. Compared with Example 2, this structure adjusted the size of the composite heat storage layer 2 (diameter 13 mm, thickness 3 mm) and changed the thickness of the air gap layer 3 (5 mm) to study the effect of structural parameters on performance.

[0065] Comparative Example 3

[0066] Based on Example 4, the spectrally selective aerogel layer 1 was replaced with ordinary optical glass of the same thickness, while all other conditions remained unchanged.

[0067] 1. Performance testing of optical-driven photothermal conversion storage and under convection environments.

[0068] Building such Figure 5 The test platform shown integrates a simulated solar light source, a wind speed control device, a data acquisition system, and an environmental chamber. It is used to evaluate the photothermal conversion efficiency of the device under different irradiance intensities and convection conditions. Indoor photothermal conversion experiments were conducted on Example 2 and Comparative Example 1. The tests were performed at an irradiance of 1.0 kW·m². -2 Conduct the experiment under conditions where wind speed is adjustable, and record the temperature change curve, such as... Figure 6 As shown. Experimental results show that the thermal storage efficiency of the uncovered thermal storage unit is only 29.2%, with a peak temperature of 332.6 K; when covered with ordinary glass as in Comparative Example 1, the thermal storage time is 630 s, and the peak temperature reaches 360.4 K; while when covered with the spectrally selective aerogel layer 1 of Example 2, the thermal storage time is shortened to 520 s, the temperature rises to 372.5 K at 2200 s, the photothermal storage efficiency reaches 87.5%, and the highest thermal storage temperature reaches 381 K. (The last sentence appears to be incomplete and possibly refers to a time period of 2 m·s.) -1Under wind speed conditions, its efficiency remained at 77.1%, and the heat storage time increased by only 5.2%. Its temperature fluctuation coefficient was reduced by 11% compared to conventional glass-covered systems, demonstrating excellent resistance to convective heat loss and operational stability. Furthermore, the device in Example 2 was tested under different solar irradiance intensities, and the results are as follows... Figure 7 As shown. When the irradiation intensity is 1.5 kW·m -2 At that time, the photothermal storage efficiency reached 91.5%; even at 0.3 kW·m -2 Even under low-light conditions, the efficiency still exceeds 50%, indicating that the device has good adaptability over a wide irradiation range. Comparing the thermal storage performance of Example 1 (aerogel covering) and Comparative Example 1 (glass covering) demonstrates the advantages of the spectrally selective aerogel layer 1 in improving photothermal efficiency and resisting environmental interference. During nighttime operation, the spectrally selective aerogel layer 1 dissipates heat to deep space through mid-infrared radiation, driving the phase change material to solidify and store cold energy, achieving a maximum cooling power of 118.8 W·m³. -2 The minimum cold storage temperature can be 4-6K lower than the ambient temperature.

[0069] 2. Simulation of thermal storage performance with different air layer thicknesses.

[0070] based on Figure 1 The structure shown was used to establish a three-dimensional (3D) unsteady-state heat conduction-phase change coupled numerical model. The model solved the energy conservation equation and used the equivalent heat capacity method (or enthalpy method) to handle the latent heat absorption and release of the phase change material (PCM) in the composite thermal storage layer during melting and solidification. The thermal properties of each layer, such as thermal conductivity (λ), density (ρ), and specific heat capacity (Cp), were set based on experimental measurements. Based on this, the thermal storage performance of Examples 2, 3, and Comparative Example 2 was simulated and analyzed. All simulations were performed at a power level of 1.0 kW·m³. -2 The simulation was conducted under solar irradiation conditions. The simulation results are as follows: Figure 8 As shown, the heat storage rate of Comparative Example 2 (without an air layer, 0 mm) is slightly faster than that of Examples 2 (3 mm) and 3 (5 mm), while Example 2 is slightly faster than Example 3. However, in actual experiments, it was found that when the spectrally selective aerogel layer 1 is in direct contact with the composite heat storage layer 2, the phase change material easily seeps out during the melting process and contaminates the surface of the spectrally selective aerogel layer 1, resulting in a significant decrease in its solar spectral transmittance (the measured decrease is more than 15%), thereby limiting the heat storage efficiency. Considering that the efficiency improvement brought by removing the air gap layer 3 is limited, while the risk of contamination is high, a 3 mm thick air gap layer 3 is preferred as the standard configuration.

[0071] 3. Simulation of annual energy savings on global land.

[0072] Based on daytime solar thermal storage efficiency and nighttime radiative cooling performance, combined with historical meteorological data from typical global climate zones, the annual energy-saving potential of the system was simulated using the device in Example 2. This system achieves synergistic energy saving through daytime solar thermal conversion and nighttime radiative cooling; the total energy-saving potential consists of two parts: daytime stored thermal energy and nighttime captured cold energy. Calculations show that the maximum global annual energy saving can reach 5321.4 MJ·m³. -2 By optimizing the phase change temperature of phase change materials across climate zones, energy-saving performance can be further improved. Compared with a unidirectional operation mode that only utilizes daytime solar thermal capture, the introduction of nighttime cold energy capture increases the system's total energy-saving potential by 45%; and compared with a unidirectional mode that only operates nighttime radiative cooling, the addition of daytime solar thermal capture function increases the total energy-saving potential by 223%.

[0073] 4. Regarding outdoor all-weather energy capture experiments.

[0074] Outdoor tests were conducted on Example 4 and Comparative Example 3. The experimental results under sunny conditions are as follows: Figure 9 As shown. The composite thermal storage layer of the device in Example 4 reached a maximum daytime temperature of 384.8 K; after radiative cooling was activated at night, the minimum temperature was 6.08 K lower than the ambient temperature, and the measured cooling power was 78 W·m. -2 Based on historical meteorological data (relative humidity 39.6%, ambient temperature 289.6K), the maximum cooling power of this device is estimated to be 118.8 W·m. -2 .

[0075] The device in Example 4 still exhibited excellent performance under partially cloudy and windy conditions. Figure 10 The temperature variations during outdoor experiments under cloudy conditions are illustrated. Compared to the glass-covered device in Comparative Example 3, the aerogel-covered device in Example 4 maintained a higher temperature during the day and exhibited stronger radiative cooling capabilities at night. Fluctuations in solar radiation caused frequent temperature changes, with a sharp drop in temperature when clouds blocked the light and a rebound when the clouds dispersed. Four significant solar radiation fluctuations were recorded, and the corresponding temperature fluctuation coefficients are shown in Table 1. When solar irradiance suddenly decreased, the average temperature fluctuation coefficient of the aerogel-covered device in Example 4 was 11% lower than that of the glass-covered device in Comparative Example 3, indicating its stronger environmental adaptability and thermal stability.

[0076] Table 1. Statistics on temperature fluctuations caused by four significant light intensity fluctuations during outdoor experiments under cloudy weather conditions.

[0077]

[0078]

[0079] Table 1 presents the statistical results of temperature fluctuations caused by four significant light intensity fluctuations during an outdoor experiment under cloudy weather conditions. The table lists the light intensity variation range and temperature decrease magnitude (ΔT) for each fluctuation. f ), initial superheat of cooling (ΔT) d The calculated temperature fluctuation coefficient (c) is used to evaluate the device's anti-interference capability.

[0080] Example 5

[0081] 1. Construction of an all-weather thermal power generation system based on bidirectional thermal energy capture

[0082] like Figure 11 and Figure 12 As shown, this embodiment provides an all-weather thermoelectric power generation system based on bidirectional thermal energy capture, including an all-weather bidirectional thermal energy collection device with a ginkgo leaf-like structure as described in Embodiment 2, a thermoelectric conversion module, and a heat dissipation structure. The thermoelectric conversion module is disposed between the all-weather bidirectional thermal energy collection device and the heat dissipation structure, and is used to convert the reversible thermal gradient formed by day and night alternation into electrical energy. In daytime mode, the hot end of the thermoelectric conversion module is in close contact with the bottom of the all-weather bidirectional thermal energy collection device, and the cold end is connected to the heat dissipation structure, utilizing the temperature difference between the high-temperature surface of the composite thermal storage layer 2 during the day and the heat dissipation structure to generate thermoelectric power. In nighttime mode, the thermoelectric conversion module is flipped so that its cold end is in close contact with the bottom of the all-weather bidirectional thermal energy collection device, and its hot end is connected to the heat dissipation structure, utilizing the temperature difference between the low temperature generated by the radiative cooling of the composite thermal storage layer 2 at night and the heat dissipation structure to generate thermoelectric power. The thermoelectric conversion module uses a commercially available bismuth-tellurium (Bi2Te3) thermoelectric module with dimensions of 15mm × 15mm × 3.5mm. The heat dissipation structure uses a copper heat sink (30mm×30mm×10mm).

[0083] 2. System performance testing

[0084] (1) Power generation performance

[0085] Simulated AM 1.5G solar spectrum (xenon lamp, 1.0 kW·m) -2 Under irradiation, the system rapidly establishes a thermal gradient. For example... Figure 13 As shown, the open-circuit voltage (VOC) stabilizes at 0.15V, corresponding to a temperature difference ΔT of 6.9K. When the irradiance is increased to four times the solar irradiance (4.0kW·m²),... -2 ) and 8 times the solar irradiance (8.0 kW·m -2 At these temperatures, ΔT reaches 19.9K and 26.5K respectively, and VOC increases to 0.52V and 0.80V. Under 8 times the solar irradiance, the system's maximum output power reaches 120mW. Based on outdoor experimental data, the system's maximum temperature difference under all-weather operation is 72.8K, and the theoretical maximum open-circuit voltage can reach 2.61V (see...).Figures 13-16 ).

[0086] (2) The effect of phase change materials on thermal stability

[0087] like Figure 15 As shown, under the same illumination conditions, the thermal decay rate of the system containing phase change material (PCM) increases from 0.11 K·s⁻¹. -1 It decreased to 0.046 K·s -1 The heat energy retention time is doubled, significantly improving the sustainability of power generation.

[0088] (3) System Expansion and Application

[0089] The two identical power generation systems were connected in parallel, and the peak voltage was measured to be 1.3V and the peak power was 210mW under one times the sunlight, successfully driving a micro fan and proving its potential for practical application.

[0090] (4) 24-hour continuous power generation capacity

[0091] like Figure 17 As shown, the voltage output of the thermoelectric device was calculated based on the temperature difference data between the composite thermal storage layer 2 and the environment obtained from outdoor measurements under clear weather conditions. The results show that the device can continuously output electrical energy around the clock and has the potential to provide uninterrupted power for low-power electronic devices.

[0092] The aforementioned photothermal storage efficiency is used to measure the efficiency of converting solar energy into thermal energy and storing it effectively. It is defined as the ratio of the latent heat stored by the phase change material to the solar radiation energy transmitted through the spectrally selective aerogel layer 1, and its expression is as follows:

[0093]

[0094] Where m is the mass of the composite thermal storage layer 2, ΔH is the latent heat, and P solar denoted as solar irradiance, S as the area of ​​the composite thermal storage layer exposed to sunlight, Δt as the phase transition duration, and T as the transmittance of the aerogel in the solar spectral band.

[0095] The temperature fluctuation coefficient of the composite thermal storage layer 2 relative to the ambient temperature is defined as the ratio of the temperature drop of the composite thermal storage layer 2 during the period when the sun is blocked by clouds to the difference between its temperature and the ambient temperature at the beginning of the cooling phase. Its expression is as follows:

[0096]

[0097] Where ΔT f ΔT represents the temperature decrease of the composite thermal storage layer 2 during one illumination fluctuation cycle (i.e., the temperature change during the fluctuation process); dThis represents the difference between the starting point of the cooling phase and the ambient temperature.

Claims

1. A 24 / 7 bidirectional cold and heat energy harvesting device with a ginkgo leaf-like structure, characterized in that, The structure consists of a spectrally selective aerogel layer and a composite heat storage layer loaded with phase change material, arranged sequentially from top to bottom. An air gap is provided between the spectrally selective aerogel layer and the composite heat storage layer. The overall structure formed by the spectrally selective aerogel layer and the composite heat storage layer is wrapped with an insulation shell. The spectrally selective aerogel layer is fixed to the top inner side of the insulation shell by interference fit, and the composite heat storage layer is detachably installed inside the insulation shell.

2. The apparatus according to claim 1, characterized in that, The thickness of the spectrally selective aerogel layer is 5-8 mm, with a transmittance of over 85% in the solar spectrum band of 0.25-2.5 μm and an emissivity of over 95% in the mid-infrared atmospheric window band of 8-13 μm.

3. The apparatus according to claim 1, characterized in that, The configuration of the composite thermal storage layer is dynamically switched according to the solar radiation intensity. When the solar irradiance is higher than or equal to 50 W·m -2 When the irradiation intensity is below 50 W·m, the composite thermal storage layer loaded with the first phase change material is activated; -2 When the first phase change material has a phase change temperature higher than the average daytime ambient temperature, it is used to absorb and store solar thermal energy during the day; the second phase change material has a phase change temperature lower than the average nighttime ambient temperature, and is used to absorb ambient cold energy at night to achieve cold energy storage.

4. The apparatus according to claim 1, characterized in that, The phase transition temperature of phase change materials is 280-420K.

5. The apparatus according to claim 1, characterized in that, The thermal conductivity of the insulation shell is 0.05 W·m. -1 ·K -1 The inner wall of the insulation shell is provided with a high-reflectivity layer.

6. The apparatus according to claim 1, characterized in that, The thickness of the air gap layer is 3-5mm, and the thickness of the composite thermal storage layer is 3-5mm.

7. The apparatus according to any one of claims 1-6, characterized in that, The method for preparing a spectrally selective aerogel layer includes the following steps: (1) Sol preparation: Tetramethoxysilane, water and methanol are mixed to promote the hydrolysis of methoxy groups to generate silanols, and a sol is obtained; (2) Catalytic gelation: Ammonia methanol solution is added to the sol to catalyze the condensation reaction, forming a three-dimensional Si-O-Si network structure, and a gel is obtained; (3) Hydrophobic modification and drying: The gel was immersed in a hexamethyldisilazane solution to replace the surface hydroxyl groups with -Si(CH3)3 groups; then it was transferred to an ethanol solution for room temperature aging; and then subjected to supercritical CO2 drying and heat treatment.

8. The apparatus according to claim 7, characterized in that: In step (1), the mass ratio of tetramethoxysilane, water, and methanol is 1.0:(0.47-0.48):(1.3-1.4); in step (2), a concentration of 2.0-3.0 mol·L⁻¹ is used. -1 Ammonia in methanol solution is used as catalyst, the volume ratio of sol to ammonia in methanol solution is 1:(60-65), the condensation reaction time is 1-2 min; in step (3), the gel is immersed in hexamethyldisilazane (HMDS) solution for more than 12 h, and the aging time is more than 7 days; the supercritical CO2 drying conditions are: 35℃, 5MPa, drying for 5-6 h; the heat treatment is to raise the temperature to 400℃ at a heating rate of 0.5℃ / min and keep it at that temperature for more than 48 h.

9. An all-weather thermoelectric power generation system based on bidirectional thermal energy capture, characterized in that, The device includes an all-weather bidirectional thermal energy collection device, a thermoelectric conversion module, and a heat dissipation structure as described in any one of claims 1-8. The thermoelectric conversion module is disposed between the all-weather bidirectional thermal energy collection device and the heat dissipation structure to convert the thermal gradient formed by the alternation of day and night into electrical energy. In daytime mode, the hot end of the thermoelectric conversion module is in close contact with the bottom of the all-weather bidirectional thermal energy collection device, and the cold end is connected to the heat dissipation structure. The thermoelectric power generation is carried out by utilizing the temperature difference between the high-temperature surface of the composite thermal storage layer and the heat dissipation structure. In nighttime mode, the thermoelectric conversion module is flipped so that its cold end is in close contact with the bottom of the all-weather bidirectional thermal energy collection device, and its hot end is connected to the heat dissipation structure. The thermoelectric power generation is carried out by utilizing the temperature difference between the low temperature generated by the composite thermal storage layer through radiative cooling and the heat dissipation structure.

10. The all-weather thermal power generation system according to claim 9, characterized in that, The thermoelectric conversion module uses thermoelectric materials based on the Seebeck effect, and the heat dissipation structure is a high thermal conductivity metal heat sink.

Images