Self-powered device and method based on natural temperature difference

Abstract

The present application relates to the technical field of temperature difference power supply, and particularly relates to a self-powered device and method based on natural temperature difference, which comprises an air-side heat exchange unit, a temperature difference power generation unit, a bidirectional heat transfer unit, a soil heat exchange unit, an energy management unit and an energy storage unit arranged in sequence from near-surface air to deep soil. The bidirectional heat transfer unit comprises a heat transfer shell and a composite capillary core coaxially arranged, and the two ends of the composite capillary core are respectively provided with a first vapor-liquid distribution cavity and a second vapor-liquid distribution cavity which are structural mirror images. Working medium is vaporized by absorbing heat at the high-temperature end, and then flows to the low-temperature end through the central vapor channel to condense. The condensed liquid returns to the high-temperature end through the vapor-liquid distribution cavity under the action of the composite capillary core, so as to realize a phase change cycle of self-adaptive heat transfer in double working conditions. The present application does not need a mechanical reversing valve, can adapt to bidirectional temperature difference changes, is compatible with variable-polarity electric energy output in opposite temperature difference directions, and is suitable for self-power supply of field low-power-consumption equipment. A corresponding temperature difference self-power supply method is also disclosed.

Description

Technical Field

[0001] This invention relates to the field of temperature difference self-powered technology, and in particular to a self-powered device and method based on natural temperature difference. Background Technology

[0002] Numerous environmental sensors, condition monitoring nodes, and low-power communication terminals are distributed in remote areas such as forests, grasslands, farmland, deserts, photovoltaic power stations, and power transmission corridors. These devices are often unattended, requiring low power for single measurements and short message communications, but the long-term power supply and maintenance costs are significant. Disposable batteries need to be replaced periodically, which is costly and poses environmental pollution risks in remote forest areas; rechargeable batteries have self-discharge and lifespan issues, making it difficult to meet the needs of continuous operation for several years; sunlight under the forest canopy is significantly affected by tree canopy shading, weather, and seasons, making a single solar power supply solution extremely unstable in dense forest environments.

[0003] Forest surface air temperature varies significantly with diurnal and seasonal changes, while deep soil temperature changes more slowly due to its greater thermal inertia. In winter and parts of spring and autumn, shallow soil temperature is higher than air temperature; in summer, air temperature may be higher than soil temperature. Studies have shown that soil temperature at a depth of 2 meters below the surface can be about 10°C higher than surface temperature in January. Researchers have explored using the natural temperature difference between soil and air, based on the Seebeck effect, for thermoelectric conversion to power forest wireless sensors. Experimental results show that, under conditions consistent with the natural forest soil-air temperature difference, the output power can reach 3.5mW. Another study, in a six-month field experiment, achieved a daily energy harvesting level of 128.74J and a peak power of 3.7mW, corresponding to a temperature difference of 6.2°C between the two sides of the thermoelectric power generation module and a soil-air temperature difference of 26.5°C. These studies verify the feasibility of using soil-air thermoelectric power generation to power low-power field devices.

[0004] Existing soil-air thermoelectric power generation devices mostly use solid heat-conducting rods, gravity-type thermosiphons, or fixed-direction heat pipes as heat transfer elements to draw underground heat to the surface and drive the thermoelectric power generation device. Two-phase closed thermosiphons rely on gravity for liquid return, with the evaporation end typically located at the bottom and the condensation end at the top, suitable for unidirectional heat transfer conditions. However, directly applying existing structures to forest environments with naturally reversed diurnal temperature variations still has the following shortcomings: Firstly, in a typical two-phase closed thermosiphon, gravity is used to return the condensate, with the evaporator end fixed at the bottom and the condenser end fixed at the top. When the heat source is moved to the surface (where the air temperature is higher than the soil temperature in summer), the direction of gravity is opposite to the direction of liquid return, severely restricting the reverse two-phase heat transfer cycle and even causing the evaporator end to dry out and heat transfer to deteriorate.

[0005] Secondly, when the circular heat pipe comes into direct contact with the planar thermoelectric power generation module, the contact area is small, which can easily generate large interfacial thermal resistance and local stress, affecting the uniform flow of heat through the thermocouple working array and potentially damaging the ceramic substrate of the thermoelectric power generation module. Summary of the Invention

[0006] To address at least one of the aforementioned technical problems, this invention proposes a self-powered device and method based on natural temperature difference, which solves the problems that existing heat transfer elements cannot adapt to changes in bidirectional temperature difference direction, leading to heat transfer failure under reverse operating conditions, and that a single thermoelectric power generation unit cannot be compatible with the variable polarity electrical energy output from two opposite temperature difference directions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention proposes a self-powered device based on natural temperature difference, comprising an air-side heat exchange unit, a thermoelectric power generation unit, a bidirectional heat transfer unit, and a soil heat exchange unit arranged sequentially from near-surface air to deep soil. The soil heat exchange unit is buried in the target soil layer underground and is used to exchange heat with the deep soil. The air-side heat exchange unit is located in the air near the ground surface and is used to absorb heat from the air for heat exchange. A thermoelectric power generation unit is used to output a low voltage with variable polarity by utilizing the bidirectional temperature difference between soil and air. The thermoelectric power generation unit has a first heat exchange surface that is thermally coupled to the air-side heat exchange unit and a second heat exchange surface that is thermally coupled to the bidirectional heat transfer unit. A bidirectional heat transfer unit includes a cylindrical heat transfer shell with one end open and containing a working medium inside, and a composite capillary core coaxially arranged inside the heat transfer shell and having a central vapor channel. A first vapor-liquid distribution cavity is formed between the open end of the heat transfer shell and the second heat exchange surface, and a second vapor-liquid distribution cavity is provided at the bottom of the heat transfer shell. The working medium is used to absorb heat and vaporize at the high-temperature end to form steam. The steam flows through the central steam channel to the low-temperature end to release heat and condense to form condensate. The condensate flows back to the high-temperature end through the first vapor-liquid distribution chamber or the second vapor-liquid distribution chamber under the action of the composite capillary, realizing a phase change cycle in which heat is adaptively transferred from the high-temperature end to the low-temperature end under dual working conditions. An energy management unit is electrically connected to the output terminal of the thermoelectric generator unit. It is used to receive the positive and negative polarity voltages output by the thermoelectric generator unit under different temperature difference directions, and to perform polarity adaptation, voltage boosting conversion and charging management. An energy storage unit, connected to the output of the energy management unit, is used to store electrical energy.

[0008] Preferably, the thermoelectric power generation unit includes a first heat exchange plate thermally coupled to the air-side heat exchange unit, a second heat exchange plate thermally coupled to the bidirectional heat transfer unit, and a thermoelectric power generation module disposed between the first heat exchange plate and the second heat exchange plate for converting thermal energy into electrical energy using the Seebeck effect. The side of the second heat spreader away from the thermoelectric power generation module is a concave arc surface. The opening end of the heat transfer shell is enclosed by a gradually widening conical connecting section and the concave arc surface to form the first vapor-liquid distribution cavity, which facilitates vapor condensation and reflux.

[0009] Preferably, the thermoelectric power generation module has a first heat exchange surface and a second heat exchange surface on both sides. A thermally conductive interface layer is provided between the first heat exchange surface and the first heat exchange plate and between the second heat exchange surface and the second heat exchange plate. The thermally conductive interface layer is used to fill the micro-unevenness of the assembly surface, reduce the contact thermal resistance, and make the heat evenly distributed. The thermoelectric power generation unit is provided with a heat insulation ring around its periphery, which is used to prevent heat from being transferred to the outside of the thermoelectric power generation unit.

[0010] Preferably, the composite capillary core includes a fine-pore capillary layer that is attached to the inner wall of the heat transfer shell to provide a capillary pressure differential for driving the condensate backflow, and a high-permeability liquid-conducting layer that is coaxially attached to the inner wall of the fine-pore capillary layer to reduce the flow resistance of the condensate along the long-distance backflow path; the fine-pore capillary layer and the high-permeability liquid-conducting layer cooperate to enable the condensate to continuously backflow from the low-temperature end to the high-temperature end to vaporize and form a phase change cycle.

[0011] Preferably, the device further includes a heat insulation layer sleeved on the outer periphery of the heat transfer shell located in the deep soil layer, the heat insulation layer being located on the upper part of the soil heat exchange unit and not in contact with it; The insulation layer divides the heat transfer shell into a first heat exchange section buried in the soil and exchanging heat with the soil heat exchange unit, a second heat exchange section located in the near-surface air, and an insulating transmission section located between the first heat exchange section and the second heat exchange section. The first vapor-liquid distribution cavity and the second vapor-liquid distribution cavity are located at the ends of the first heat exchange section and the second heat exchange section, respectively, away from the adiabatic transmission section.

[0012] Preferably, the soil heat exchange unit includes heat exchange fins connected to the first heat exchange section and a thermally conductive backfill layer filled between the heat exchange fins.

[0013] Preferably, the energy management unit includes: The polarity adapter module has its input terminal electrically connected to the output terminal of the thermoelectric generator unit, and is used to convert the bidirectional voltage with bidirectional polarity change output by the thermoelectric generator unit into a rectified voltage with fixed polarity. The cold start and boost module has its input terminal electrically connected to the output terminal of the polarity adapter module, and is used to perform boost conversion when the input voltage reaches the preset start-up condition. The output regulation unit has its input terminal electrically connected to the output terminal of the cold start and boost module, and its output terminal electrically connected to the input terminal of the energy storage unit. It is used to charge the energy storage unit and limit the output voltage. The energy storage status detection and load control unit has its input terminal electrically connected to the output of the output regulation unit, and is used to control the on / off state of the controlled load according to the energy storage voltage and the available energy of the energy storage.

[0014] Preferably, the energy storage unit includes a supercapacitor, a rechargeable battery, or a hybrid energy storage unit of a supercapacitor and a rechargeable battery.

[0015] A second aspect of the present invention provides a self-powered method based on natural temperature difference, applied to the self-powered device based on natural temperature difference as described in the first aspect, comprising the following steps: Obtain the variable polarity low voltage output from the thermoelectric generator unit; The variable polarity low voltage is converted into a fixed polarity rectified voltage through a polarity adaptation module; Determine whether the rectified voltage reaches the cold start voltage and whether the available input power reaches the cold start power; If any condition is not met, the system remains in a low-power waiting state; if all conditions are met, the boost conversion is initiated. It performs boost conversion, voltage limiting and regulation, and charging control to charge the energy storage unit; Real-time monitoring of the energy storage unit's energy storage voltage and estimation of available energy storage capacity; When the energy storage voltage reaches the start-up threshold and the available energy storage is not less than the sum of the energy consumption of a single task and the reserved energy, the controlled load is allowed to start. When the task is completed or the energy storage voltage drops to the shutdown threshold, the controlled load is disconnected and the charging state is returned; wherein the startup threshold is higher than the shutdown threshold.

[0016] Preferably, when the temperature of the deep soil is higher than the temperature of the near-surface air, the temperature of the second heat exchange surface of the thermoelectric generator unit thermally coupled with the soil heat exchange unit is higher than the temperature of the first heat exchange surface thermally coupled with the air-side heat exchange unit, forming a temperature difference and outputting a low voltage of the first polarity. When the temperature of the deep soil is lower than that of the near-surface air, the temperature of the second heat exchange surface of the thermoelectric generator is lower than that of the first heat exchange surface, forming a temperature difference and outputting a low voltage with the second polarity opposite to the first polarity.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention, by setting a composite capillary core continuously extending along a first heat exchange section, an adiabatic transmission section, and a second heat exchange section in a bidirectional heat transfer unit, and by setting a first vapor-liquid distribution cavity and a second vapor-liquid distribution cavity with mirrored structures in the first and second heat exchange sections respectively, enables both ends of the heat transfer unit to have vapor collection, condensate collection, and capillary return functions. The fine-pore capillary layer in the composite capillary core provides the capillary pressure difference to drive the condensate return flow, and the high-permeability liquid-conducting layer reduces the flow resistance of the condensate along the long return path. The two work together to enable the condensate to continuously return from the low-temperature end to the high-temperature end to form a stable phase change cycle, thereby realizing the adaptive heat transfer from the high-temperature end to the low-temperature end under dual operating conditions, without the need for mechanical reversing valves or external active control, and solving the problem of heat transfer failure in existing heat pipes when the temperature difference direction is reversed.

[0018] 2. This invention automatically converts the bidirectional polarity-changing voltage output by the thermoelectric generator unit into a fixed polarity rectified voltage through the polarity adaptation module in the energy management unit. In conjunction with the cold start and boost module, output regulation unit, and energy storage status detection and load control unit, it completes the boost conversion, charging management, and load on / off control, so that a single thermoelectric generator unit can be compatible with the electrical energy output from two opposite temperature difference directions without the need for external switch switching or additional thermoelectric module groups.

[0019] 3. In this invention, the side of the second heat spreader of the thermoelectric generator unit that connects to the bidirectional heat transfer unit is set as a concave arc surface, and is connected to the open end of the heat transfer shell through a gradually widening conical connecting section. The concave arc surface, the gradually widening conical connecting section and the open end of the heat transfer shell together form a first vapor-liquid distribution cavity. This structure provides a large condensation area at the condensation end, which is conducive to uniform vapor condensation. At the same time, it facilitates the return of condensate to the composite capillary wick along the arc surface, effectively reducing the interfacial thermal resistance and improving the heat transfer efficiency. Attached Figure Description

[0020] Figure 1 A three-dimensional diagram of a self-powered device based on natural temperature difference; Figure 2 A front view of a self-powered device based on natural temperature difference; Figure 3 for Figure 2 Sectional view along axis AA; Figure 4 An isometric sectional view of a self-powered device based on natural temperature difference; Figure 5 This is a schematic diagram of the structure of the first vapor-liquid distribution chamber in this invention; Figure 6 An exploded view of a self-powered device based on natural temperature differences; Figure 7 This is a system block diagram of the energy management unit in this invention; Figure 8 This is a flowchart of a dual-condition power generation method based on natural temperature difference.

[0021] In the diagram: 10. Air-side heat exchange unit; 20. Thermoelectric power generation unit; 21. First heat spreader; 22. Second heat spreader; 221. Concave arc surface; 23. Thermal interface layer; 24. Thermal insulation ring; 25. Thermoelectric power generation module; 30. Bidirectional heat transfer unit; 31. Heat transfer shell; 311. First heat exchange section; 312. Second heat exchange section; 313. Insulating transmission section; 32. Composite capillary core; 321. Fine-pore capillary layer; 322. High-permeability liquid guiding layer; 33. Central vapor channel; 34. First vapor-liquid distribution chamber; 35. Second vapor-liquid distribution chamber; 36. Insulation layer; 37. Connecting section; 40. Soil heat exchange unit; 50. Energy Management Unit; 51. Polarity Adaptation Module; 52. Cold Start and Boost Module; 53. Output Regulation Unit; 54. Energy Storage Status Detection and Load Control Unit; 60. Energy storage unit. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments of the present invention.

[0023] Example 1

[0024] Please refer to Figures 1-6 As shown, this embodiment provides a dual-condition adaptive thermoelectric power generation device based on the temperature difference between deep soil and air. The device is vertically buried, using ambient air above the surface and relatively stable soil at the target depth as two heat exchange boundaries. From top to bottom, the device includes an air-side heat exchange unit 10, a thermoelectric power generation unit 20, a bidirectional heat transfer unit 30, an insulation layer 36, and a soil heat exchange unit 40; an energy management component and an energy storage unit 60 are also electrically connected to the thermoelectric output side.

[0025] The structure of each component of this device and their interconnections are described in detail below with reference to the accompanying drawings.

[0026] Please refer to Figures 1-5As shown, in this embodiment, the air-side heat exchange unit 10 is disposed above the ground surface and includes an air-side heat exchanger for exchanging heat with the ambient air through natural convection, radiation, or an auxiliary heat exchange structure. The air-side heat exchanger may have a structure with densely packed fins. The base is thermally connected to the first heat spreader 21 of the thermoelectric generator unit 20 below, and the vertical fins extend upwards to increase the effective heat exchange area with the air.

[0027] Meanwhile, the air-side heat exchanger is preferably made of a metal with good thermal conductivity, such as copper, aluminum, or their alloys. When the air temperature is low, the air-side heat exchanger acts as the heat release end, discharging heat from the ground to the ambient air; when the air temperature is high, the air-side heat exchanger acts as the heat absorption end, absorbing heat from the ambient air and sending the heat to the thermoelectric power generation unit 20. Regardless of the direction of heat flow, the air-side heat exchanger establishes a thermal connection with the upper side of the thermoelectric power generation module 25 through the first heat spreader 21, rather than directly bridging to the deep end of the bidirectional heat transfer unit 30.

[0028] Please refer to Figures 1-4 As shown, in this embodiment, the thermoelectric power generation unit 20 is disposed between the air-side heat exchanger and the first heat exchange section 311 of the bidirectional heat transfer unit 30, and is a sandwich-type component through which heat must pass and be converted into electrical energy. Specifically, the thermoelectric power generation unit 20 includes a first heat spreader 21, a thermoelectric power generation module 25, a second heat spreader 22, a heat insulation ring 24, and a thermally conductive interface layer 23.

[0029] Specifically, the first heat exchanger 21 is located above the thermoelectric power generation module 25 and is thermally connected to the air-side heat exchanger; the second heat exchanger 22 is located below the thermoelectric power generation module 25 and is thermally connected to the first heat exchange section 311 of the bidirectional heat transfer unit 30. The first heat exchanger 21 and the second heat exchanger 22 respectively constitute large-area planar heat exchange components on both sides of the thermoelectric module, used to spread heat from the air side or the soil side on the module contact surface, reducing local heat flow concentration and interfacial thermal resistance caused by point contact. The first heat exchanger 21 and the second heat exchanger 22 are preferably made of copper or a high thermal conductivity composite material.

[0030] To compensate for microscopic unevenness of the assembly surface, increase the actual contact area, reduce contact thermal resistance, and ensure that heat enters and leaves the thermoelectric power generation module 25 more evenly, in this embodiment, a thermally conductive interface layer 23 is provided between the first heat exchange plate 21 and the first heat exchange surface of the thermoelectric power generation module 25; another thermally conductive interface layer 23 is also provided between the second heat exchange surface of the thermoelectric power generation module 25 and the second heat exchange plate 22.

[0031] It is understood that the thermal interface layer 23 can be made of thermal grease, thermal pad, thermal phase change material, graphite thermal sheet or metal thermal foil, etc., preferably a high-performance thermal interface material with a thermal conductivity of not less than 3W / (m·K), and the thickness is controlled between 0.1mm and 0.5mm.

[0032] It should be noted that the thermoelectric power generation module 25 is the core component that utilizes the Seebeck effect to convert the temperature difference between the two sides into a low DC voltage. It mainly includes a first ceramic substrate and a second ceramic substrate, multiple sets of P-type and N-type thermoelectric arms disposed between the two ceramic substrates, and metal interconnecting electrodes connecting adjacent P-type and N-type thermoelectric arms. The P-type and N-type thermoelectric arms are connected in series in the circuit and in parallel in the heat transfer direction. The two ceramic substrates provide electrical insulation, mechanical support, and heat transfer for the internal thermoelectric arms and interconnecting electrodes. The outer surface facing the first heat spreader 21 constitutes the first heat exchange surface of the thermoelectric power generation module 25, and the outer surface facing the second heat spreader 22 constitutes the second heat exchange surface of the thermoelectric power generation module 25. The thermoelectric power generation module 25 is preferably made of Bi2Te3-based thermoelectric material.

[0033] In this embodiment, the effective heat exchange area of ​​the thermoelectric power generation module 25 can be defined as the orthographic projection area of ​​the thermocouple working array inside the thermoelectric power generation module 25 on the first and second heat exchange surfaces. The areas where the ceramic substrate edge encapsulation strip, fastening holes, and thermal insulation ring 24 are located are not part of the effective heat exchange area. Therefore, the area that needs to ensure uniform heating, uniform pressure, and stable temperature difference is the area in the center of the module corresponding to the thermocouple array.

[0034] Please refer to Figure 2 and Figure 3 As shown, in this embodiment, the aforementioned heat insulation ring 24 is arranged around the thermoelectric power generation module 25, outside the effective heat exchange area. Specifically, the heat insulation ring 24 can be made of a heat insulation material with a low thermal conductivity (such as polyurethane foam, phenolic foam, aerogel felt, etc.) to prevent the periphery of the module from becoming a bypass for preferential heat conduction.

[0035] It should be noted that the spatial sequence of the main heat path in this embodiment is: air-side heat exchanger → first heat spreader 21 → thermal interface layer 23 → thermoelectric generator module 25 → thermal interface layer 23 → second heat spreader 22 → first heat exchange section 311. It can be understood that the first heat exchange section 311 only terminates and is thermally connected to the lower side of the second heat spreader 22, does not penetrate the thermoelectric generator module 25, and does not form a continuous metal thermal bridge with the air-side heat exchanger that bypasses the thermoelectric generator module 25. This forces the main heat between the air end and the soil end to undergo thermoelectric conversion through the thermoelectric generator module 25.

[0036] As an optimized solution of this embodiment, the thermoelectric power generation unit 20 may further include a sealing element, a pre-tightening connection element, an elastic pre-tightening element, and an insulating bushing.

[0037] Specifically, the sealing element provides a seal or protection for the adjacent interfaces of the laminated assembly, preventing external environmental factors such as moisture and sediment from directly entering the module edge or interface. The pre-tightening connector and the elastic pre-tightening element are located on the outer periphery of the effective heat exchange area, bridging the upper and lower laminated components, and applying controlled clamping force to the first heat spreader 21, the thermally conductive interface layer 23, the thermoelectric power generation module 25, and the second heat spreader 22. The elastic pre-tightening element compensates for thermal expansion and contraction, processing errors, and minor deformations of the assembly surface, ensuring the module maintains a relatively stable interface compression state during long-term thermal cycling. An insulating bushing is placed between the pre-tightening connector and the adjacent thermally conductive element, preventing the metal fastening path from directly becoming a high-thermal-conductivity bypass between the air and soil sides, thereby reducing the thermal bridge formed by the fasteners.

[0038] Please refer to Figure 3 and Figure 4 As shown, the bidirectional heat transfer unit 30 described above in this embodiment is a key structure for achieving continuous energy harvesting even when the temperature difference direction is reversed. Specifically, the bidirectional heat transfer unit 30 includes a heat transfer shell 31, a continuous composite capillary core (including a fine-pore capillary layer 321 and a high-permeability liquid-conducting layer 322), a central vapor channel 33 working medium, and a first vapor-liquid distribution chamber 34 and a second vapor-liquid distribution chamber 35 located at both ends of the heat transfer shell 31.

[0039] Specifically, the heat transfer shell 31 constitutes the sealed outer shell and mounting frame of the bidirectional heat transfer unit 30, and internally contains the working medium, continuous composite capillary core and central steam channel 33. Among them, the heat transfer shell 31 is divided axially by the insulation layer 36 into a first heat exchange section 311 near the thermoelectric power generation unit 20, an insulated transmission section 313 in the middle and a second heat exchange section 312 located in the target soil layer underground.

[0040] As a preferred embodiment, the first heat exchange section 311 and the second heat exchange section 312 can be made of different materials than the adiabatic transmission section 313. Specifically, the first heat exchange section 311 and the second heat exchange section 312 can be made of metal materials with high thermal conductivity (such as copper, oxygen-free copper, or silver-copper alloy, with a thermal conductivity of not less than 300 W / (m·K)) to achieve efficient heat exchange with external heat sources (the second heat spreader 22 of the thermoelectric power generation unit 20 or deep soil), ensuring that heat can quickly pass through the pipe wall into the internal working medium or be transferred from the internal working medium to the outside of the pipe wall. The adiabatic transmission section 313 can be made of metal materials with relatively low thermal conductivity (such as stainless steel, titanium alloy, or nickel-based alloy, with a thermal conductivity in the range of 10 W / (m·K) to 50 W / (m·K)), whose thermal conductivity is much lower than that of the first and second heat exchange sections 312.

[0041] Understandably, the use of differentiated materials in the heat transfer shell 31 allows external heat from the first heat exchange section 311 and the second heat exchange section 312, made of high thermal conductivity materials, to pass through the pipe wall into the interior of the heat transfer shell 31 with minimal temperature difference loss (at the evaporation end), or allows internal heat to be efficiently transferred through the pipe wall to the outside (at the condensation end), thus improving end heat exchange efficiency. Simultaneously, the adiabatic transmission section 313, made of low thermal conductivity materials, significantly reduces the solid thermal conductivity along the axial direction of the heat transfer shell 31, allowing heat to be transferred primarily in the form of latent heat of phase change of the working medium within the adiabatic transmission section 313, rather than through direct conduction via the metal pipe wall. Furthermore, the adiabatic transmission section 313 is covered with an insulation layer 36. The low thermal conductivity pipe wall material and the outer insulation layer 36 form a double insulation barrier, further reducing radial heat loss to the surrounding environment when traversing shallow soil, ensuring that heat is concentrated inside the heat transfer shell 31 and transferred axially. In terms of manufacturing process, the first heat exchange section 311, the heat transfer section 313 and the second heat exchange section 312 can be reliably connected by brazing, friction welding or laser welding and other connection processes to ensure the overall sealing and structural strength of the heat transfer shell 31.

[0042] In this embodiment, the working medium is filled inside the heat transfer shell 31, absorbing heat and vaporizing at the high-temperature end and releasing heat and condensing at the low-temperature end. Specifically, the working medium is preferably water, ethanol, acetone, ammonia, or a mixture of the aforementioned substances, more preferably deionized water or ultrapure water. The filling amount can be determined according to the internal volume of the heat transfer shell 31 and the porosity of the continuous composite capillary core, and is usually 30% to 60% of the total pore volume of the composite capillary core.

[0043] The first vapor-liquid distribution chamber 34 is located within the first heat exchange section 311, and the second vapor-liquid distribution chamber 35 is located within the second heat exchange section 312. Both the first vapor-liquid distribution chamber 34 and the second vapor-liquid distribution chamber 35 are connected to the central steam channel 33 and the continuous composite capillary wick.

[0044] Specifically, the side of the second heat spreader 22 connected to the bidirectional heat transfer unit 30 is a concave arc surface 221. The open end of the heat transfer shell 31 is connected to the concave arc surface 221 through a gradually widening conical connecting section 37. The concave arc surface 221, the gradually widening conical connecting section 37 and the open end of the heat transfer shell 31 together form the first vapor-liquid distribution cavity 34.

[0045] Understandably, when the concave arc surface 221 of the first vapor-liquid distribution chamber 34 serves as the condensation end, it provides a large condensation area, which is conducive to the uniform condensation of vapor on the arc surface. After the condensed liquid is collected on the concave arc surface 221, the droplets flow naturally along the arc surface to the wall of the gradually widening conical connecting section 37 under the assistance of gravity, and then flow into the continuous composite capillary wick. This structure facilitates the return of condensate and avoids liquid stagnation. At the same time, the gradually widening conical connecting section 37 makes the vapor channel gradually widen. After the vapor enters the distribution chamber, the flow rate gradually decreases, which is conducive to the full diffusion of vapor and contact with the concave arc surface 221, thereby improving the condensation efficiency. When the first vapor-liquid distribution chamber 34 serves as the evaporation end, the concave arc surface 221 receives heat uniformly from the second heat spreader 22. The space between the arc surface and the end of the composite capillary wick provides sufficient phase change space for the vaporization of the working medium. The vapor can smoothly flow into the central vapor channel 33 through the gradually widening conical connecting section 37.

[0046] It should be noted that the structure of the second vapor-liquid distribution chamber 35 can be mirror-symmetrical with that of the first vapor-liquid distribution chamber 34, so that when the temperature difference direction is reversed, the second vapor-liquid distribution chamber 35 can perform the same function as the first vapor-liquid distribution chamber 34, thereby realizing adaptive phase change cycle under bidirectional operating conditions.

[0047] Please refer to Figure 4 As shown, in this embodiment, the aforementioned continuous composite capillary extends continuously along the first heat exchange section 311, the adiabatic transmission section 313, and the second heat exchange section 312, and maintains continuous liquid flow at the two closed ends. The continuous composite capillary includes a fine-pore capillary layer 321 close to the inner wall of the heat transfer shell 31 and a high-permeability liquid-conducting layer 322 located between the fine-pore capillary layer 321 and the central vapor channel 33.

[0048] Specifically, the fine-pore capillary layer 321 is disposed on the outside of the high-permeability liquid-conducting layer 322 (i.e., on the side near the inner wall of the heat transfer shell 31), and the high-permeability liquid-conducting layer 322 is disposed on the inside of the fine-pore capillary layer 321 (i.e., on the side near the central vapor channel 33). The inner and outer layer arrangement of the fine-pore capillary layer 321 and the high-permeability liquid-conducting layer 322 in this example is mainly based on the following considerations: First, the fine-pore capillary layer 321 is closely attached to the inner wall of the heat transfer shell 31, enabling it to maximize the use of the entire circumferential wall surface of the heat transfer shell 31 for liquid collection and transfer. Specifically, since the inner wall of the heat transfer shell 31 is the surface where the condensate first contacts and adheres, arranging the fine-pore capillary layer 321 here ensures that the condensate is captured by the capillary structure as soon as it forms, eliminating the possibility of liquid stagnation or the formation of dead zones on smooth wall surfaces. Simultaneously, the fine-pore capillary layer 321 is arranged circumferentially around the entire heat transfer shell 31, resulting in an effective liquid collection circumference far greater than that of point-like or strip-like capillary structures, significantly improving liquid capture efficiency.

[0049] Second, the fine-pore capillary layer 321 needs to provide sufficient capillary driving force to overcome the reverse gravity (up to several meters of liquid column). Specifically, the arrangement close to the inner wall of the heat transfer shell 31 ensures that the direction of the capillary force is consistent with the axis of the heat transfer shell 31, enabling the liquid to directly drive the liquid to flow back from the condenser end to the evaporator end along the entire length of the heat transfer shell 31. If the fine-pore capillary layer 321 is arranged on the inner side and the high-permeability layer is arranged on the outer side, the condensate must first penetrate the high-permeability layer to reach the fine-pore capillary layer 321, which not only increases the liquid migration path and flow resistance, but also may form a liquid stagnation zone between the high-permeability layer and the inner wall of the heat transfer shell 31, weakening the continuity of capillary return.

[0050] Third, the high-permeability liquid-conducting layer 322 is disposed inside the fine-pore capillary layer 321, close to the central vapor channel 33, enabling it to receive liquid seeping from the inner wall of the fine-pore capillary layer 321 and providing a low-resistance axial return channel for the liquid. Specifically, the large pore size and high porosity of the high-permeability liquid-conducting layer 322 ensure minimal pressure drop when the liquid flows a long distance axially. Simultaneously, the high-permeability liquid-conducting layer 322 is adjacent to the central vapor channel 33, and its inner wall actually forms part of the boundary of the vapor channel. This arrangement allows the vapor to exert shear force on the liquid surface of the high-permeability liquid-conducting layer 322 when flowing within the central channel, assisting the liquid's axial movement and, under specific operating conditions, helping to improve the return liquid capacity.

[0051] Fourth, the fine-pore capillary layer 321 and the high-permeability liquid-conducting layer 322 are closely bonded (surface contact or partial interlocking), forming a "fine outer, coarse inner" composite structure in the radial direction. Specifically, the condensate is first captured by the outer fine-pore capillary layer 321 and capillary driving force is established. Subsequently, under the action of radial capillary pressure difference, it naturally permeates into the inner high-permeability liquid-conducting layer 322. This radially series liquid path design allows the liquid to obtain both the high capillary driving force provided by the fine-pore capillary layer 321 and low-resistance long-distance transport in the high-permeability liquid-conducting layer 322, thus superimposing the functional advantages of the two different pore size levels.

[0052] Understandably, the composite capillary core in this embodiment serves to distribute the two contradictory functional requirements of "generating capillary driving force" and "reducing liquid reflux pressure drop" to different layers. Specifically, the outer fine-pore capillary layer 321 is responsible for liquid absorption and establishing capillary pressure difference, while the inner high-permeability liquid-conducting layer 322 is responsible for forming a liquid reflux channel with low resistance. Since these two layers continuously extend to both ends of the component, the reflux direction of the working medium can be reversed along with the heat flow direction, without relying on the gravity reflux conditions at the fixed upper or lower end.

[0053] In this embodiment, the continuous composite capillary core, composed of the fine-pore capillary layer 321 and the high-permeability liquid-conducting layer 322, extends almost the entire length of the heat transfer shell 31, and is connected to the first vapor-liquid distribution chamber 34 and the second vapor-liquid distribution chamber 35 at both ends, respectively. The continuity of the composite capillary core ensures that, regardless of the direction of heat flow, the condensate can always flow continuously back from the low-temperature end to the high-temperature end along the inner wall of the heat transfer shell 31 under capillary drive, without any interruption of the return flow due to capillary core interruption.

[0054] In this embodiment, the high-permeability liquid-conducting layer 322 has a hollow channel at its center, naturally forming a central vapor channel 33 for vapor circulation. Specifically, the vapor generated at the high-temperature end mainly flows to the other end through this central channel (a very small amount of vapor may flow through the fine-pore capillary layer 321 and the high-permeability liquid-conducting layer 322), while the liquid generated by condensation at the low-temperature end mainly enters the composite capillary core surrounding the central channel for reflux, forming a spatial separation between the forward transport of vapor and the reverse reflux of condensate, reducing the interference of the opposite flow of vapor and liquid.

[0055] Understandably, the central steam channel 33 provides a low-resistance channel for steam, enabling it to flow quickly from the high-temperature end to the low-temperature end. Its flow cross-sectional area is much larger than the pore size of the composite capillary core, ensuring that the steam pressure drop is much smaller than the capillary driving pressure difference and does not become a limiting factor for heat transfer capacity.

[0056] The synergistic effect of the above structures enables the bidirectional heat transfer unit 30 to adaptively switch the flow direction of vapor and condensate according to the change in temperature difference without the need for external mechanical valves or active control elements, thus completing a stable bidirectional phase change heat transfer cycle.

[0057] It should be noted that, in this embodiment, the bidirectional heat transfer unit 30 needs to simultaneously meet the requirements for heat transfer and capillary return capacity during actual operation. Specifically: First, the temperature difference between the two sides of the thermoelectric power generation module 25 and the total thermal resistance of the entire heat transfer path jointly determine the heat flow rate required to be transferred through the bidirectional heat transfer unit 30, and this heat flow rate must match the maximum heat transfer capacity of the heat transfer unit; Second, in the phase change cycle of the working medium, the driving force required for the condensate to flow back from the condensation end to the evaporation end is entirely provided by the capillary pressure difference provided by the fine-pore capillary layer 321. This capillary pressure difference must be greater than the sum of all resistances on the return path (including liquid phase flow resistance, vapor pressure drop, gravity head, and necessary safety margins), otherwise the capillary wick will dry out and heat transfer will deteriorate. Therefore, the size design of the bidirectional heat transfer unit 30 must simultaneously meet the following two sets of constraints.

[0058] Specifically, for any heat transfer direction ( ,in" "This indicates the first operating condition where the temperature of the deep soil is higher than the ambient air temperature." "This indicates the second operating condition where the ambient air temperature is higher than the deep soil temperature." The necessary condition for capillary liquid return is:

[0059] in, The capillary driving pressure differential provided to the fine-pore capillary layer, in Pa; The liquid phase flow pressure drop of the condensate flowing back from the condensing end to the evaporating end along the composite capillary core, in Pa; The vapor pressure drop along the central vapor channel from the evaporator to the condenser, expressed in Pa. The gravitational head required to overcome for condensate reflux in this direction, in Pa; This is a safety margin and a local loss margin, measured in Pa, used to cover uncertainties such as deviations in working fluid properties, manufacturing tolerances, and long-term performance degradation.

[0060] The capillary-driven pressure differential is determined by the equivalent pore size of the fine capillary layer:

[0061] in, The surface tension of the working medium liquid, in N / m; The effective contact angle between the working medium and the capillary wick material, in rad; The equivalent capillary radius of the fine capillary layer is expressed in meters (m).

[0062] This formula shows that the equivalent aperture The smaller the pore size, the greater the capillary driving force. However, excessively small pore sizes will increase the resistance to liquid flow, so they need to be used in conjunction with a high-permeability liquid-conducting layer.

[0063] The liquid phase pressure drop, which is the flow resistance of the condensate flowing back from the condensation end to the evaporation end along the composite capillary, is approximately:

[0064] in, The dynamic viscosity of the working medium liquid, in Pa·s; This is the reflux length of the liquid in the composite capillary core in this direction, in meters. It can be taken as [value missing] when the liquid flow path is equal to the length of the entire heat transfer unit. ; The mass flow rate of the liquid phase circulation in this direction is expressed in kg / s. The density of the working medium liquid, in kg / m³ 3 ; The equivalent permeability of the composite capillary core in this direction, in meters. 2 ; The effective liquid flow area of ​​the composite capillary core in this direction, in meters (m²). 2 .

[0065] This equation shows that the liquid phase pressure drop is related to the reflux length. and mass flow It is directly proportional to the equivalent permeability of the composite capillary core. and effective circulation area Inversely proportional. The purpose of setting up a high-permeability liquid-conducting layer is precisely to increase... and This is to reduce the liquid phase pressure drop during long-distance reflux.

[0066] The vapor pressure drop is the flow resistance of vapor along the central vapor channel from the evaporation end to the condensation end.

[0067] in, Let be the Darcy friction factor of the vapor channel in this direction, which is dimensionless; This represents the length of the vapor flow along the central channel in this direction, in meters (m). This is the hydraulic diameter of the steam channel in this direction, in meters (m). For a circular channel... That is, the inner diameter of the channel; This represents the density of the working medium vapor in this direction, in kg / m³. 3 ; This represents the average steam velocity in this direction, in m / s. The central steam passage uses a larger diameter to increase... This reduces the vapor pressure drop, preventing it from becoming a limiting factor for heat transfer.

[0068] Among them, hydraulic diameter It can be further written as:

[0069] in, The cross-sectional area of ​​the steam passage in this direction, in meters (m²). 2 ; The wetted perimeter of the steam passage cross-section in this direction, in meters. Average steam velocity. It can be written as:

[0070] in, This represents the steam mass flow rate in this direction, expressed in kg / s.

[0071] The gravitational pressure drop is the gravitational head that needs to be overcome when the condensate returns.

[0072] in, Acceleration due to gravity, unit: m / s² 2 Take 9.8 m / s2 ; This represents the unfavorable upward rise of the condensate in this direction, expressed in meters (m). In a vertically arranged device, when the evaporator is located above the condenser (e.g., in the first operating condition, the condenser is above and the evaporator is below, and the condensate flows downward against gravity due to capillary force), the condensate flows back down. A positive value indicates that capillary force needs to overcome gravity; when the evaporator is below the condenser, gravity actually helps the liquid return. It can take negative values ​​or zero. This formula is used to calculate the gravitational effect in the most unfavorable direction.

[0073] On the other hand, the heat transfer capacity must meet the heat flow requirements. The required heat transfer is determined by the available temperature difference across the thermoelectric power generation module and the total thermal resistance.

[0074] in, The effective heat transfer temperature on the deeper soil side in this direction, in K (or °C). The effective heat transfer temperature on the ambient air side in this direction, in K (or °C). This represents the total thermal resistance along the entire heat transfer path from deep soil to ambient air in this direction, expressed in K / W. This formula shows that the heat transfer is directly proportional to the temperature difference and inversely proportional to the total thermal resistance.

[0075] The total thermal resistance is the sum of the thermal resistances of each stage along the heat transfer path:

[0076] in, The thermal resistance of air-side heat transfer in this direction (including the convective thermal resistance between the air-side heat exchanger and the environment), in K / W; The sum of the contact thermal resistances of each heat-conducting interface layer (including the interfaces between the first and second heat-spreading plates and the thermoelectric power generation module, and between the thermoelectric power generation module and the bidirectional heat transfer unit) in this direction, in K / W. The equivalent thermal resistance of the thermoelectric power generation module in this direction is expressed in K / W. The equivalent thermal resistance of the bidirectional heat transfer unit in this direction is expressed in K / W. The thermal resistance on the soil side in this direction (including the thermal resistance of the heat exchange fins, the thermally conductive backfill layer, and the thermal conductivity and convection of the deep soil) is expressed in K / W. The above thermal resistances can only be directly added when they are in the same series thermal path; therefore, the main heat transfer path of this device is a series structure.

[0077] In this embodiment, the equivalent thermal resistance of the bidirectional heat transfer unit is approximately:

[0078] in, The effective heat transfer length of the bidirectional heat transfer unit in this direction, in meters; The equivalent thermal conductivity of the bidirectional heat transfer unit in this direction is expressed in W / (m·K). This equivalent thermal conductivity takes into account the combined contributions of heat transfer due to phase change of the working fluid, heat conduction of the composite capillary wick, and heat conduction of the tube wall, and is much higher than the thermal conductivity of a single metal material. This represents the equivalent heat transfer cross-sectional area of ​​the bidirectional heat transfer unit in this direction, in meters (m²). 2 .

[0079] In this embodiment, the maximum heat transfer capacity of the heat transfer unit is limited by the capillary limit—that is, the amount of heat transfer corresponding to the maximum circulating working fluid flow rate that can be driven by the capillary pressure difference.

[0080] in, The latent heat of vaporization of the working medium is expressed in J / kg. This represents the maximum circulating mass flow rate that satisfies the capillary pressure difference constraint in this direction, expressed in kg / s. It can be fully defined as:

[0081] This definition shows that, To achieve capillary pressure difference Driven by this, it can overcome the liquid phase pressure drop. (follow) Increase and increase), vapor pressure drop (follow) (increases and increases), gravitational pressure drop and safety margin The maximum mass flow rate of the sum.

[0082] The structural design of the bidirectional heat transfer unit must ensure that the required heat transfer in both heat transfer directions does not exceed the capillary limit heat transfer.

[0083] If a conservative heat transfer capability is required for both operating conditions, it can be written as:

[0084] The above formulas together constitute the design criteria for bidirectional heat transfer units. Specifically, the required heat transfer is first determined based on the temperature difference conditions of the target site and the total thermal resistance of the heat transfer path. Then select an appropriate capillary pore size. (Determines capillary driving force), composite capillary core permeability and circulation area (Determines liquid phase resistance), vapor channel diameter (Determines the vapor pressure drop) so that even in the most unfavorable direction (the direction of greatest gravitational resistance), the capillary pressure difference is still sufficient to overcome all resistance and maximize heat transfer capacity. Not less than .

[0085] When both of the above conditions are met, the bidirectional heat transfer unit can maintain stable phase change cycle heat transfer in both opposite temperature difference directions, thereby ensuring that the thermoelectric power generation module can obtain usable temperature difference for power generation in different seasons throughout the year.

[0086] Please refer to Figure 4 As shown, in this embodiment, the aforementioned insulation layer 36 covers the outside of the heat transfer section 313 of the bidirectional heat transfer unit 30, mainly used to isolate the interference of shallow soil temperature fluctuations on the main heat path. The insulation layer 36 is made of a low thermal conductivity insulation material, such as rigid polyurethane foam, extruded polystyrene board (XPS), aerogel insulation felt, or vacuum insulation board, etc., preferably a closed-cell foam material with a thermal conductivity not exceeding 0.04 W / (m·K) and good water resistance. The insulation layer 36 does not cover the second heat exchange section 312 that needs to exchange heat with the target soil layer, so that the second heat exchange section 312 can still fully exchange heat with the target depth soil layer through the soil heat exchange unit 40.

[0087] Please refer to Figures 1-3 As shown, in this embodiment, the soil heat exchange unit 40 is installed within the target underground soil layer and includes heat exchange fins and a heat-conducting backfill layer. Specifically, the second heat exchange section 312 is thermally connected to the heat exchange fins. The heat exchange fins can be annular, longitudinal, or spiral fins, preferably a combination of annular and longitudinal fins. The material is copper, aluminum, or their alloys, the fin thickness is 0.5mm to 3mm, and the fin spacing is 5mm to 30mm. The heat-conducting backfill layer fills the gaps between the heat exchange fins, the second heat exchange section 312, and the surrounding undisturbed soil. It uses a high thermal conductivity backfill material (such as thermally conductive cement mortar, bentonite mixture mixed with graphite powder, etc.), preferably with a thermal conductivity of not less than 1.5W / (m·K), so that heat can be transferred from the second heat exchange section 312 to the deep soil, or from the deep soil to the second heat exchange section 312.

[0088] Please refer to Figure 7 As shown, in this embodiment, the energy management component is electrically connected to the output terminal of the thermoelectric generator module 25, and is used to process the variable polarity weak electrical energy under two heat flow directions into stable electrical energy that can be stored and used. The energy management component consists of a polarity adaptation unit, a cold start and boost unit, an output regulation unit 53, and an energy storage status detection and load control unit 54.

[0089] Specifically, the polarity adaptation unit includes a low-loss polarity conversion network and a reverse current blocking branch. The low-loss polarity conversion network is used to convert inputs of opposite polarities in two operating states into a fixed polarity output acceptable to the subsequent stage, preferably using a synchronous rectifier with low on-state voltage drop or an ideal diode rectifier bridge; the reverse current blocking branch is used to prevent reverse discharge from the energy storage terminal to the thermoelectric module side.

[0090] The cold start and boost unit includes an input voltage or input power detection branch, a start-up energy storage branch, and a self-starting boost conversion branch. The input voltage or input power detection branch is used to determine whether the rectified voltage reaches the cold start voltage. Does the available input power reach the cold start power? And whether the duration has been reached The starting energy storage branch establishes starting energy when the starting conditions are met; the self-starting boost conversion branch uses a boost DC-DC converter with low input voltage start-up capability, and starts boost conversion when the input voltage is as low as 0.3V to 0.5V.

[0091] The output regulation unit 53 includes a charging control branch, a voltage limiting and regulating branch, and an anti-backflow branch. The charging control branch executes the corresponding charging strategy according to the type of energy storage unit 60 (constant current-constant voltage charging for supercapacitors and pre-charge-constant current-constant voltage charging for batteries); the voltage limiting and regulating branch clamps the output voltage within a safe range; and the anti-backflow branch prevents the energy storage terminal from discharging backwards to the previous stage.

[0092] The energy storage status detection and load control unit 54 includes an energy storage detection branch, a hysteresis comparison branch, a load switch, and a control signal interface. The energy storage detection branch acquires the energy storage status and estimates the available energy. ; Hysteresis comparison branch setting start threshold and the closing threshold and To avoid frequent start-stop cycles when energy storage is at its critical point; the load switch connects or disconnects the downstream controlled load based on the energy storage voltage and available energy; the control signal interface is used to interact with external controllers.

[0093] The energy storage unit 60 can be a supercapacitor, a rechargeable battery, or a hybrid energy storage unit of both, used to absorb the long-term, low-power, fluctuating output of the thermoelectric power generation module, and to provide energy buffer for the downstream stage during short-term high-power tasks or when the temperature difference is insufficient.

[0094] It is understood that the device in this embodiment has two operating conditions during operation: First operating condition: The temperature of the deep soil is higher than the ambient air temperature. Specifically, when the temperature of the deep soil is higher than the ambient air temperature, heat is transferred from the underground end to the air end. The external heat path is: deep soil → heat-conducting backfill layer → heat exchange fins → second heat exchange section 312 → inside the bidirectional heat transfer unit 30 → first heat exchange section 311 → second heat spreader 22 → thermoelectric generator module 25 → first heat spreader 21 → air-side heat exchanger → ambient air. Under this condition, the working medium absorbs heat and vaporizes near the second heat exchange section 312 and the second vapor-liquid distribution chamber 35. The vapor flows upward along the central vapor channel 33 to the first vapor-liquid distribution chamber 34 and the first heat exchange section 311, where it releases heat and condenses at the lower temperature at the upper end. The condensate enters the high-permeability liquid-conducting layer 322 and the fine-pore capillary layer 321, and returns to the second heat exchange section 312 along the inner wall of the heat transfer shell 31 under the capillary pressure difference provided by the fine-pore layer. The thermoelectric generator module 25 outputs a low voltage of the first polarity at this time.

[0095] Second operating condition: The ambient air temperature is higher than the deep soil temperature. Specifically, when the ambient air temperature is higher than the deep soil temperature, the flow directions of all heat, vapor, and liquid are reversed compared to the above operating condition. Heat enters from the air-side heat exchanger, passes through the first heat spreader 21, the thermoelectric generator module 25, the second heat spreader 22, and the first heat exchange section 311 to the bidirectional heat transfer unit 30, and then enters the deep soil through the second heat exchange section 312, heat exchange fins, and thermally conductive backfill layer. The working medium absorbs heat and vaporizes near the first heat exchange section 311 and the first vapor-liquid distribution chamber 34. The vapor flows downward along the central vapor channel 33 to the second vapor-liquid distribution chamber 35 and the second heat exchange section 312 and condenses. The condensate enters the high-permeability liquid-conducting layer 322 and the fine-pore capillary layer 321 from the second vapor-liquid distribution chamber 35, and flows back to the first heat exchange section 311 by relying on the capillary pressure difference. The output polarity of the thermoelectric generator module 25 reverses as the hot and cold surfaces are interchanged, but it still enters the energy storage unit 60 through the same polarity adaptation and energy management link.

[0096] The switching between the two operating conditions does not require mechanical valves or active control. The basis for this is: the first and second vapor-liquid distribution chambers 35 are set; the continuous composite capillary core is continuously connected; the central vapor channel 33 is separated from the capillary return liquid channel; and both ends can respectively undertake the functions of evaporation and condensation.

[0097] In summary, the dual-condition adaptive thermoelectric power generation device based on the temperature difference between deep soil and air provided in this embodiment, through a bidirectional heat transfer unit 30 with vapor-liquid distribution chambers at both ends and a through-type continuous composite capillary core, combined with an energy management component capable of accepting bipolar voltage input, achieves spontaneous, continuous, and efficient thermoelectric conversion and power management under two opposite operating conditions: soil temperature higher than air temperature and air temperature higher than soil temperature. This device has a compact structure, no moving parts, and requires no external energy input, making it particularly suitable for providing a long-term, stable power supply for low-power outdoor equipment.

[0098] Example 2

[0099] Please refer to Figure 8 As shown, this embodiment provides a self-powered method based on natural temperature difference, applied to the self-powered device based on natural temperature difference described in Embodiment 1. The self-powered method includes the following steps: S1: Obtain the variable polarity low voltage output from the thermoelectric generator module 25.

[0100] Specifically, the thermoelectric power generation module 25 utilizes the temperature difference between the first heat exchange surface and the second heat exchange surface to generate a thermoelectric voltage. As the relationship between soil temperature and air temperature varies with the seasons and day and night, the polarity of this voltage changes with the direction of the temperature difference, and the amplitude changes with the magnitude of the temperature difference, typically ranging from 0.5V to 5V.

[0101] When the temperature of the deep soil is higher than the temperature of the ambient air, heat is transferred from the deep soil to the air through the soil heat exchange unit 40, the bidirectional heat transfer unit 30, the thermoelectric power generation module 25, and the air-side heat exchange unit 10. The thermoelectric power generation module 25 outputs a first polarity voltage. When the temperature of the ambient air is higher than the temperature of the deep soil, heat is transferred from the air-side heat exchange unit 10 to the deep soil through the thermoelectric power generation module 25, the bidirectional heat transfer unit 30, and the soil heat exchange unit 40. The thermoelectric power generation module 25 outputs a second polarity voltage.

[0102] S2: A fixed polarity rectified voltage is obtained through a low-loss polarity conversion network, and reverse current blocking branch is used to prevent backflow at the energy storage end.

[0103] Specifically, regarding polarity adaptation, the two output terminals of the thermoelectric generator unit 20 are connected to the two input terminals of the polarity adaptation circuit. The polarity adaptation circuit preferably employs a low-voltage rectifier structure with full-wave polarity conversion capability (e.g., an active rectifier bridge composed of four low-threshold NMOS transistors or an ideal diode bridge). Internally, it includes a first conduction path and a second conduction path. When the input is a voltage of the first polarity, the first conduction path is activated, outputting the input voltage with a fixed polarity (e.g., the positive terminal of the output is a fixed terminal); when the input is a voltage of the second polarity, the second conduction path is activated, similarly converting the input voltage to the same fixed polarity output. This implementation, through path-selective conduction, ensures that the subsequent boost circuit and energy storage circuit do not need to switch connection directions with changes in temperature difference direction, achieving "polarity-insensitive" energy input.

[0104] Specifically, regarding reverse current blocking, a reverse current blocking unit is connected in series in the energy transmission path from the thermoelectric generator unit 20 to the energy storage module. It should be noted that this unit can employ an ideal diode controller in conjunction with a MOSFET with low on-resistance.

[0105] S3: Determine whether the rectified voltage has reached the cold start voltage, whether the available input power has reached the cold start power, and whether the duration has reached the set time; if any condition is not met, maintain the low power waiting state; if all conditions are met, allow cold start and perform boost conversion.

[0106] Specifically, the input voltage or input power detection branch monitors the rectified voltage and input power output by the polarity adapter unit in real time. The rectified voltage value is then compared with a preset cold start voltage threshold. The input power value is compared with the preset cold start power threshold. Compare and detect whether the duration has been reached. If any condition is not met, the cold start and boost unit maintains a low-power standby mode (static current controlled below 1μA); when all conditions are met, the energy storage branch is started to build up startup energy, and the self-starting boost conversion branch activates the boost conversion.

[0107] Cold start voltage Cold start power and duration The calibration is based on cold start characteristics, measured energy consumption of a complete mission, and environmental derating factor.

[0108] S4: Performs boost conversion, voltage limiting and regulation, and charging regulation to charge the energy storage unit 60.

[0109] Specifically, the self-starting boost converter branch boosts the rectified voltage to the target output voltage (e.g., set as the charging voltage of the energy storage unit). The output regulation unit 53 performs voltage limiting and regulation on the boosted voltage: the voltage limiting and regulation branch clamps the output voltage within a safe range (e.g., limiting a single lithium-ion battery to 4.2V±1%), and the charging control branch executes the corresponding charging strategy according to the type of energy storage unit (constant current-constant voltage charging for supercapacitors, and pre-charge-constant current-constant voltage charging for batteries). The backflow prevention branch prevents the energy storage terminal from discharging backwards to the front stage.

[0110] S5: Estimate the available energy storage capacity and allow the load to start when the energy storage voltage reaches the start-up threshold and the available energy storage capacity is not less than the sum of the energy consumption of a single task and the reserved energy.

[0111] Specifically, the energy storage detection branch continuously monitors the terminal voltage of the energy storage unit 60 and estimates the available energy storage. When the energy storage unit is a capacitor, the available energy within the hysteresis interval is calculated according to... The estimation is performed, where C is the capacitance of the capacitor; when the energy storage unit is a battery, it is estimated based on the state of charge, available capacity, and allowable depth of discharge. The above estimation method can reflect the actual energy that the energy storage unit can release within the hysteresis interval between the start-up threshold and the shutdown threshold, and is used to determine whether it is sufficient to support a complete load task.

[0112] The hysteresis comparison branch in the energy storage state detection and load control unit 54 compares the current energy storage voltage with a preset start-up threshold. Compare and estimate the available energy storage Energy consumption per mission and reserved energy The sums are compared. Only when the energy storage voltage reaches the activation threshold... and Only when the load is started is the load allowed to start.

[0113] Energy consumption per mission The power required for a single working cycle of the load can be determined by actual measurement; reserve energy. Used to cover static loss, low-temperature derating, retry transmission, or task interruption preservation. Startup threshold. and the closing threshold satisfy The difference between the two constitutes the hysteresis interval, which avoids the load from frequently starting and stopping and oscillating near the critical point of the energy storage voltage.

[0114] S6: Connect the load and wake up the external controller.

[0115] Specifically, when all conditions in step S5 are met, the load switch closes, the energy storage unit is connected to the external controlled load, and the external controller is activated to execute a predetermined task. It should be noted that in this embodiment, the controlled load includes, but is not limited to, wireless sensing nodes, including a controller, environmental sensors, and a wireless communication unit.

[0116] S7: Performs the scheduled task while continuously monitoring the energy storage voltage.

[0117] Specifically, after the external controller is woken up, it executes a predetermined task (such as data acquisition, processing and transmission). During the execution of the task, the energy storage detection branch continuously detects the terminal voltage of the energy storage unit.

[0118] S8: When the task is completed or the energy storage voltage drops to the shutdown threshold, disconnect the controlled load and return to the charging process.

[0119] Specifically, after the controlled load completes its predetermined task, the energy storage status detection and load control unit controls the load switch to disconnect, cutting off the power supply to the load, and the device returns to the charging process (i.e., restarting from step S1). If the energy storage voltage drops to the shutdown threshold during load operation... If the energy storage status detection and load control unit forcibly disconnects the load switch to protect the energy storage unit from over-discharge, it then returns to the charging process.

[0120] Taking the energy storage unit as a capacitor as an example, the start-up threshold With the closing threshold The available energy corresponding to the hysteresis interval between them is:

[0121] This estimate is used for load initiation determination in step S5 to ensure that the energy stored in the hysteresis interval is sufficient to complete at least one full task.

[0122] The energy management method provided in this embodiment achieves reliable and controllable power supply to downstream loads under conditions of extremely unstable thermoelectric power input through automatic polarity adaptation, cold start condition judgment, energy storage available energy budget, and hysteresis load control, thereby improving the overall energy utilization efficiency and long-term operational reliability of the device.

[0123] The above description is a specific implementation of the embodiments of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A self-powered device based on natural temperature difference, characterized in that, It includes an air-side heat exchange unit (10), a thermoelectric power generation unit (20), a bidirectional heat transfer unit (30), and a soil heat exchange unit (40) arranged sequentially from near-surface air to deep soil. Soil heat exchange unit (40) is buried in the target soil layer underground and is used to exchange heat with deep soil. An air-side heat exchange unit (10) is installed in the air near the ground surface and is used to absorb heat from the air for heat exchange. Thermoelectric generator unit (20) is used to output a low voltage with variable polarity by utilizing the bidirectional temperature difference between soil and air. The thermoelectric generator unit (20) is thermally coupled to the air-side heat exchange unit (10) and the bidirectional heat transfer unit (30). The bidirectional heat transfer unit (30) includes a cylindrical heat transfer shell (31) with one end open and containing a working medium inside, and a composite capillary core (32) coaxially arranged inside the heat transfer shell (31) and having a central vapor channel (33). The opening end of the heat transfer shell (31) and the thermoelectric generator unit (20) form a first vapor-liquid distribution chamber (34). The bottom of the heat transfer shell (31) is provided with a second vapor-liquid distribution chamber (35). The working medium is used to absorb heat and vaporize at the high temperature end to form steam. The steam flows through the central steam channel (33) to the low temperature end to release heat and condense to form condensate. The condensate flows back to the high temperature end through the first vapor-liquid distribution chamber (34) or the second vapor-liquid distribution chamber (35) under the action of the composite capillary (32), realizing the phase change cycle of adaptive heat transfer from the high temperature end to the low temperature end under dual working conditions. The energy management unit (50) is electrically connected to the output terminal of the thermoelectric generator unit (20) and is used to receive the positive and negative polarity voltages output by the thermoelectric generator unit (20) under different temperature difference directions, and to perform polarity adaptation, voltage boosting and charging management. An energy storage unit (60) is connected to the output terminal of the energy management unit (50) and is used to store electrical energy.

2. The self-powered device based on natural temperature difference according to claim 1, characterized in that, The thermoelectric power generation unit (20) includes a first heat exchange plate (21) thermally coupled to the air-side heat exchange unit (10), a second heat exchange plate (22) thermally coupled to the bidirectional heat transfer unit (30), and a thermoelectric power generation module (25) disposed between the first heat exchange plate (21) and the second heat exchange plate (22) for converting thermal energy into electrical energy using the Seebeck effect; The side of the second heat spreader (22) away from the thermoelectric power generation module (25) is a concave arc surface (221). The opening end of the heat transfer shell (31) is enclosed by the concave arc surface (221) through the gradually widening conical connecting section (37) to form the first vapor-liquid distribution cavity (34) which facilitates vapor condensation and reflux.

3. The self-powered device based on natural temperature difference according to claim 2, characterized in that, The thermoelectric power generation module (25) has a first heat exchange surface and a second heat exchange surface on both sides. A thermal interface layer (23) is provided between the first heat exchange surface and the first heat distribution plate (21) and between the second heat exchange surface and the second heat distribution plate (22). The thermal interface layer (23) is used to fill the micro-unevenness of the assembly surface, reduce the contact thermal resistance, and make the heat evenly distributed. The thermoelectric power generation unit (20) is provided with a heat insulation ring (24) on its outer periphery, which is used to block heat from being transferred to the outside of the thermoelectric power generation unit (20).

4. The self-powered device based on natural temperature difference according to claim 1, characterized in that, The composite capillary core (32) includes a fine-pore capillary layer (321) that is attached to the inner wall of the heat transfer shell (31) to provide a capillary pressure differential for driving the condensate backflow, and a high-permeability liquid-conducting layer (322) that is coaxially attached to the inner wall of the fine-pore capillary layer (321) to reduce the flow resistance of the condensate along the long-distance backflow path; the fine-pore capillary layer (321) and the high-permeability liquid-conducting layer (322) cooperate to enable the condensate to continuously backflow from the low-temperature end to the high-temperature end to vaporize and form a phase change cycle.

5. The self-powered device based on natural temperature difference according to claim 1, characterized in that, The device also includes a heat insulation layer (36) sleeved on the outer periphery of the heat transfer shell (31) located in the deep soil portion, the heat insulation layer (36) being located on the upper part of the soil heat exchange unit (40) and not in contact with each other; The insulation layer (36) divides the heat transfer shell (31) into a first heat exchange section (311) buried in the soil and exchanging heat with the soil heat exchange unit (40), a second heat exchange section (312) located in the near-surface air, and an insulating transmission section (313) located between the first heat exchange section (311) and the second heat exchange section (312). The first vapor-liquid distribution chamber (34) and the second vapor-liquid distribution chamber (35) are located at the ends of the first heat exchange section (311) and the second heat exchange section (312) away from the adiabatic transmission section (313), respectively.

6. The self-powered device based on natural temperature difference according to claim 5, characterized in that, The soil heat exchange unit (40) includes heat exchange fins connected to the first heat exchange section (311) and a heat-conducting backfill layer filled between the heat exchange fins.

7. The self-powered device based on natural temperature difference according to claim 1, characterized in that, The energy management unit (50) includes: The polarity adapter module (51) has its input terminal electrically connected to the output terminal of the thermoelectric generator unit (20) and is used to convert the bidirectional voltage with bidirectional polarity change output by the thermoelectric generator unit (20) into a rectified voltage with fixed polarity. The cold start and boost module (52) has its input terminal electrically connected to the output terminal of the polarity adapter module (51) and is used to perform boost conversion when the input voltage reaches the preset start condition; The output regulation unit (53) has its input terminal electrically connected to the output terminal of the cold start and boost module (52) and its output terminal electrically connected to the input terminal of the energy storage unit (60). It is used to charge the energy storage unit (60) and limit the output voltage. The energy storage status detection and load control unit (54) has its input terminal electrically connected to the output of the output regulation unit (53) and is used to control the on / off state of the controlled load according to the energy storage voltage and the available energy of the energy storage.

8. The self-powered device based on natural temperature difference according to claim 1, characterized in that, The energy storage unit (60) includes a supercapacitor, a rechargeable battery, or a hybrid energy storage unit (60) of a supercapacitor and a rechargeable battery.

9. A self-powered method based on natural temperature difference, applied to the self-powered device based on natural temperature difference as described in any one of claims 1-8, characterized in that, Includes the following steps: Obtain the variable polarity low voltage output from the thermoelectric generator unit (20); The variable polarity low voltage is converted into a fixed polarity rectified voltage by the polarity adapter module (51); Determine whether the rectified voltage reaches the cold start voltage and whether the available input power reaches the cold start power; If any condition is not met, the system remains in a low-power waiting state; if all conditions are met, the boost conversion is initiated. Perform boost conversion, voltage limiting and regulation and charging control to charge the energy storage unit (60); Real-time detection of the energy storage voltage of the energy storage unit (60) and estimation of the available energy storage; When the energy storage voltage reaches the start-up threshold and the available energy storage is not less than the sum of the energy consumption of a single task and the reserved energy, the controlled load is allowed to start. When the task is completed or the energy storage voltage drops to the shutdown threshold, the controlled load is disconnected and the charging state is returned; wherein the startup threshold is higher than the shutdown threshold.

10. The self-powered method based on natural temperature difference according to claim 9, characterized in that, When the temperature of the deep soil is higher than that of the near-surface air, the temperature of the second heat exchange surface of the thermoelectric generator unit (20) and the soil heat exchange unit (40) is higher than that of the first heat exchange surface of the heat exchange unit (10) on the air side, forming a temperature difference and outputting a low voltage of the first polarity. When the temperature of the deep soil is lower than that of the near-surface air, the temperature of the second heat exchange surface of the thermoelectric generator unit (20) is lower than that of the first heat exchange surface, forming a temperature difference and outputting a low voltage of the second polarity opposite to the first polarity.

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