Frozen ground thermal rod and repair method for failed frozen ground thermal rod

Abstract

This invention discloses a permafrost heat pipe and a method for repairing failed permafrost heat pipes. The permafrost heat pipe includes: a heat pipe shell with a filling cavity and a sealing element at the upper opening, the filling cavity being filled with phase change material; a working heat pipe, the lower end of which passes through the sealing element and is coaxially inserted into the filling cavity, the upper end of which is located above the sealing element; and a volume expansion absorption unit, which is an elastically expandable strip structure. The lower end of the volume expansion absorption unit passes through the sealing element but is not coaxially inserted into the filling cavity, so as to absorb the volume change of the phase change material during the phase change process through its own volume expansion and contraction. The upper end of the volume expansion absorption unit extends out of the sealing element and is located outside the heat pipe shell. This invention achieves 24-hour long-term cooling of permafrost through a composite mode of phase change material cold storage and relay heat transfer, and is suitable for the repair of failed heat pipes and the protection of permafrost foundations in roadbeds, pipelines, and other projects in permafrost areas.

Description

Technical Field

[0001] This invention belongs to the field of basic technology of frozen soil engineering, specifically relating to frozen soil heat pipes and methods for repairing failed frozen soil heat pipes. Background Technology

[0002] In permafrost regions, heat pipes, as a highly efficient active cooling device, have been widely used in various permafrost projects such as highways, railways, bridges, and power transmission towers due to their core advantages of unidirectional heat transfer, no need for external energy, and stable operation. They have become a key technical means to alleviate permafrost degradation and ensure the stability of projects.

[0003] The working principle of the heat pipe is based on gas-liquid two-phase circulating heat transfer. Its lower heat-absorbing section (also known as the evaporation section) is buried in the permafrost layer, while the upper heat-releasing section is exposed above the ground. The interior is filled with a low-boiling-point working fluid such as liquid ammonia (also known as the condensation section). In winter, the heat in the permafrost layer is absorbed by the working fluid, causing it to evaporate into a gaseous state and rise to the heat-releasing section. The heat is then dissipated into the air through the heat-releasing section. After the gaseous working fluid condenses into a liquid state, it flows back to the heat-absorbing section under the action of gravity, forming a cyclical one-way cooling process. This continuously removes heat from the permafrost layer, increasing the upper limit of the permafrost, maintaining the frozen state and mechanical strength of the permafrost.

[0004] Despite their excellent cooling performance and long-term service potential, heat pipes inevitably age and deteriorate under the long-term effects of the complex and extreme environment of permafrost regions (low temperatures, freeze-thaw cycles, strong ultraviolet radiation, and wind and sand erosion), ultimately leading to failure. The core causes of heat pipe failure fall into three main categories: First, the working fluid inside the pipe undergoes a chemical or electrochemical reaction with the shell material, producing non-condensable gases that form gas locks, reducing the effective condensation area, increasing thermal resistance, and deteriorating heat transfer performance. Second, the organic working fluid decomposes under extreme temperatures over a long period or reacts with the shell material, leading to a deterioration of the working fluid's thermophysical properties and loss of heat transfer capacity. Third, the shell material dissolves, corrodes, or even perforates under freeze-thaw cycles and media corrosion, causing working fluid leakage and complete heat pipe failure. Furthermore, installation deviations during construction and a lack of subsequent maintenance can also accelerate heat pipe aging and shorten their service life.

[0005] When the heat pipe fails, its protective function for permafrost engineering is completely lost, which in turn triggers a series of chain reactions.

[0006] Therefore, the failure of heat pipes after long-term service has become a key hidden danger restricting the long-term stability of permafrost engineering. Summary of the Invention

[0007] The purpose of this invention is to overcome the limitations of the existing technology and provide a method for repairing frozen soil heat pipes and failed frozen soil heat pipes that can improve the repair of failed heat pipes in frozen soil areas and protect frozen soil foundations.

[0008] To achieve the above objectives, the present invention proposes a permafrost heat pipe, comprising: a heat pipe shell having a filling cavity and a sealing element at the upper opening, wherein the filling cavity is filled with a phase change material; a working heat pipe, the lower end of which passes through the sealing element and is coaxially inserted into the filling cavity, the upper end of which is located above the sealing element; and a volume expansion absorption unit, which is an elastically expandable strip structure, wherein the lower end of the volume expansion absorption unit passes through the sealing element but is not coaxially inserted into the filling cavity, so as to absorb the volume change of the phase change material during the phase change process through its own volume expansion and contraction, and the upper end of the volume expansion absorption unit extends out of the sealing element and is located outside the heat pipe shell.

[0009] In one alternative embodiment, the phase change material is one or more combinations of organic alkanes, polyols, inorganic eutectic salts, or brine systems.

[0010] In one optional embodiment, the phase change material has a phase change point of -10°C to -20°C.

[0011] In one optional embodiment, the volume expansion absorption unit includes: a shrink tube inserted into the filling cavity and in contact with the phase change material; and an expansion bladder disposed at the other end of the shrink tube and located outside the heat rod shell, the expansion bladder and the shrink tube forming a closed cavity.

[0012] In one alternative embodiment, the shrink tube is a thin-walled metal tube or a plastic hose, and the expansion bladder is a cuboid or elliptical structure made of metal or plastic.

[0013] In one optional embodiment, the working heat rod includes: an evaporation section inserted into the filling cavity; and a condensation section disposed at one end of the evaporation section and located on the upper part of the heat rod shell; wherein the outer surfaces of the evaporation section and the condensation section are respectively provided with a plurality of fins along the axial direction.

[0014] In one alternative implementation, the condensation section includes at least two branch structures.

[0015] In one alternative embodiment, the end of the evaporation section is integrally formed with a V-shaped structure to connect the two branch structures.

[0016] In one alternative embodiment, the outer diameter of the evaporation section is 30% to 60% of the inner diameter of the heat pipe shell.

[0017] On the other hand, the present invention also proposes a method for repairing a failed permafrost heat pipe, comprising: cutting off the failed permafrost heat pipe, leaving the buried part as the heat pipe shell; inserting a working heat pipe and a volume expansion absorption unit into the filling cavity respectively; filling the filling cavity of the heat pipe shell with phase change material; sealing the upper end of the buried part with a sealing element, such that the lower end of the working heat pipe passes through the sealing element and is coaxially inserted into the filling cavity, and the upper end of the working heat pipe is located above the sealing element; the lower end of the volume expansion absorption unit passes through the sealing element but is not coaxially inserted into the filling cavity, so as to absorb the volume change of the phase change material during the phase change process through its own volume expansion and contraction, and the upper end of the volume expansion absorption unit extends out of the sealing element and is located outside the heat pipe shell. The beneficial effects of this invention are: (1) It is simple and quick, and can effectively repair failed heat pipes; (2) The working state of the repaired heat pipe is more stable and long-lasting. Through the coordinated design of the heat pipe shell, working heat pipe and volume expansion absorption unit, a composite mode of phase change material cold storage + relay heat transfer is used to realize 24-hour long-lasting cooling of frozen soil: at night, the working heat pipe quickly collects pulsed cold energy and stores it in the phase change material, and during the day, the phase change material slowly releases cold energy to continuously cool the frozen soil. At the same time, the volume expansion absorption unit compensates for the volume change of the phase change material to ensure stable operation of the device. It solves the technical limitation of conventional heat pipes that only cool at night in winter. It is suitable for the repair of failed heat pipes and the protection of frozen soil foundations in roadbeds, pipelines and other projects in frozen soil areas. Attached Figure Description

[0018] Figure 1 This is a cross-sectional view of a frozen soil heat pipe provided in one embodiment of the present invention. Figure 2 This is a schematic front view of the expansion absorption unit of the frozen soil heat pipe provided in one embodiment of the present invention. Figure 3 This is a schematic diagram of the working structure of the frozen soil heat pipe provided in one embodiment of the present invention.

[0019] Explanation of reference numerals in the attached drawings: 1-Hot rod shell; 2-Phase change material; 3-Bulk expansion absorption unit; 31-Contraction tube; 32-Expansion bladder; 4-Sealing element; 5-Working hot rod; 51-Condensation section; 52-Condensation section fins; 53-Evaporation section; 54-Evaporation section fins. Detailed Implementation

[0020] In related technologies, the failure of heat pipes completely negates their protective function for permafrost engineering, triggering a series of chain reactions that seriously threaten the stability and safety of engineering structures. The main impacts are manifested in four aspects: First, the thermal balance of permafrost is disrupted, the cooling mechanism of the permafrost layer fails, and against the backdrop of intensified climate warming and humidification, the rate of permafrost degradation accelerates significantly, the upper limit of permafrost continues to shift downwards, the thickness of the permafrost layer decreases, and ice-rich and ice-saturated permafrost melts, leading to a significant decrease in the bearing capacity and shear strength of the permafrost, making it unable to effectively support the superstructure. Second, it exacerbates frost heave and thaw settlement disasters in the roadbed. In summer, the roadbed in sections where the failed heat pipe is located will experience uneven settlement due to permafrost thawing, resulting in pavement cracking, potholes, and structural loosening. In winter, uneven expansion of the permafrost layer will cause frost heave, leading to roadbed deformation and pavement damage, severely affecting the traffic efficiency and safety of transportation engineering, exhibiting characteristics similar to those of untreated permafrost roadbeds. Third, it causes irreversible damage to structures such as bridges, culverts, and power transmission towers. Permafrost thawing leads to foundation settlement and tilting, causing cracks, misalignment, and even structural instability, increasing maintenance costs and shortening the service life of the project. Fourth, it damages the permafrost ecosystem surrounding the project. Permafrost thawing can lead to surface subsidence and vegetation degradation, further exacerbating the ecological deterioration of the permafrost region. Additionally, corrosion of the casing and leakage of the working fluid from failed heat pipes may cause minor pollution to the surrounding soil and water, increasing the difficulty of ecological restoration.

[0021] Because heat pipes are high-vacuum containers filled with volatile working fluids, damage to the pipes, corrosion of the welds, and cracks can all cause heat pipe failure. Due to the complex manufacturing process of heat pipes and the need for specialized equipment, on-site handling and restoration are difficult. Heat pipe restoration technology has always been a challenge in permafrost engineering and has remained unresolved for a long time.

[0022] This application addresses this problem primarily through phase change heat absorption, intermittent and relay heat transfer modes, and long-term cooling modes. Research indicates that heat pipes mainly cool the permafrost beneath the foundations of highways, railways, and power transmission lines in permafrost regions. This means the heat pipes can only operate under specific environmental and permafrost conditions, namely, in winter and at night when the ambient temperature is lower than the permafrost temperature, allowing them to dissipate heat from the permafrost. However, the characteristics of winter temperatures in cold regions like the Qinghai-Tibet Plateau are large temperature fluctuations. Furthermore, the heat transfer process between the evaporation section of the heat pipe buried in the permafrost and the permafrost is conduction, a slow heat transfer process within the soil. This results in the heat pipes only being able to operate in winter, and specifically at night. This leads to a significant contradiction between the heat pipes' pulsed super-forced cooling and the slow heat transfer of the soil. While nighttime temperatures can reach -20°C to -30°C, or even -40°C, the surface temperature of the heat pipes during the day is only a few degrees below zero, or even slightly above zero, under intense sunlight. Thus, the pulsed cooling at night lasts only 8 to 10 hours. Furthermore, the cold energy generated during this cooling period is difficult to transfer quickly to the surrounding frozen soil, resulting in the heat pipes' operating efficiency being only 30% to 40% of the designed efficiency.

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 As shown, according to an embodiment of the present invention, in one aspect, a permafrost heat pipe is provided, including a heat pipe shell 1, a working heat pipe 5, and a volume expansion absorption unit 3. The heat pipe shell 1 has a filling cavity and a sealing element 4 is provided at the upper opening. The filling cavity is filled with a phase change material 2. The working heat pipe 5 has its lower end penetrating through the sealing element 4 and coaxially inserted into the filling cavity. The upper end of the working heat pipe 5 is located above the sealing element 4. The volume expansion absorption unit 3 is an elastically expandable strip structure. The lower end of the volume expansion absorption unit 3 penetrates through the sealing element 4 but is not coaxially inserted into the filling cavity, so as to absorb the volume change of the phase change material 2 during the phase change process through its own volume expansion and contraction. The upper end of the volume expansion absorption unit extends out of the sealing element 4 and is located outside the heat pipe shell 1.

[0025] In this embodiment, the heat pipe shell 1 can be the shell of a failed heat pipe. The heat pipe shell 1 is typically a cylindrical structure with one open end and one closed end, with a sealing element 4 at the open end for sealing. One end of the working heat pipe 5 passes through the sealing element 4 and is inserted into the filling cavity formed by the heat pipe shell 1. The lower end of the working heat pipe 5 extends to the lower middle part of the filling cavity to ensure full contact with the phase change material 2, while the upper end extends out of the sealing element 4 and is exposed to the atmosphere above the ground surface. The closed end of the heat pipe shell 1 is buried in the permafrost layer, and the open end is located above the ground surface. A filling cavity is formed inside the shell. The volume of the filling cavity is designed according to the on-site permafrost cooling requirements and the phase change volume change rate of the phase change material 2 to ensure that the amount of phase change material 2 filled meets the cold storage requirements, while reserving sufficient space to accommodate the volume expansion absorption unit 3.

[0026] The working heat pipe 5 is a high-efficiency heat-conducting component, a uniquely shaped gravity-fed heat pipe with an internal vacuum, filled with a working medium, accounting for approximately 30% of its internal space. The working medium is one or more combinations of liquid nitrogen and Freon. The working heat pipe 5 possesses superconducting heat transfer capabilities, particularly its rapid heat release performance at night. Cold energy is rapidly conducted through the tube wall and fins 54 of the evaporation section 53 of the working heat pipe 5 to the interior of the phase change material 2 within the filling cavity, achieving rapid cold energy input through large-area contact.

[0027] The cavity is filled with phase change material 2, which can store a large amount of cold energy through the latent heat of the liquid-to-solid phase change process of phase change material 2; and the working heat pipe 5 is in contact with phase change material 2, which can transfer heat quickly. Thus, through the combination of the two, the pulsed cold energy transferred by the heat pipe at night can be absorbed quickly and efficiently.

[0028] The volume expansion absorption unit 3 also penetrates the seal 4 and is inserted into the filling cavity, arranged parallel to the working heat pipe 5. The lower end of the volume expansion absorption unit 3 is inserted into the phase change material 2, and the upper end extends out of the seal 4. The volume expansion absorption unit 3 is an elastically deformable cavity structure, which can be filled with inert gas or use an elastic metal bellows structure. Its core function is to absorb the volume change of the phase change material 2: the phase change material 2 will shrink in volume during the liquid to solid phase change process and expand in volume during the solid to liquid phase change process. The volume expansion absorption unit 3 offsets the volume fluctuation of the phase change material 2 through its own elastic expansion and contraction (cavity volume change), avoiding excessive pressure in the filling cavity that could cause the seal 4 to fail and the heat pipe shell 1 to deform, thus ensuring the long-term stable operation of the device.

[0029] The sealing element 4 is a conventional sealing structure, which can be a threaded sealing structure or a seal can be formed by on-site welding.

[0030] This invention breaks through the limitation of conventional heat pipes that only provide pulsed cooling during winter nights. By using a composite mode of phase change material 2 for cold storage and relay-type heat transfer, it achieves 24-hour long-term cooling of frozen soil. Phase change material 2 can quickly absorb and store the pulsed cold energy transferred by the working heat pipe 5 at night, and then continuously transfer the cold energy to the surrounding frozen soil in the form of slow heat release. This solves the core contradiction of conventional heat pipes, which suffer from untimely cold energy transfer and slow heat transfer in the soil. This significantly improves the actual working efficiency of the heat pipe from 30% to 40% of the design efficiency, effectively enhances the freezing effect of frozen soil, and delays frozen soil degradation.

[0031] The segmented process of relay heat transfer is as follows: During the nighttime phase, the working heat pipe 5 directly captures the pulsed cold energy of the underground permafrost, completing the first stage of heat absorption; Cold energy is transferred to phase change material 2, which absorbs cold energy and undergoes a phase change to store cold energy, serving as an intermediate energy storage buffer section. During the day when there is no pulsed cold source, phase change material 2 slowly releases the stored cold energy, which continues to act on the permafrost to complete the second stage of long-term heat transfer.

[0032] In this way, the limitation of traditional heat pipes, which can only provide centralized cooling at night, can be overcome. By relying on the relay cooperation of rapid cooling by the working heat pipe 5, cold storage by the phase change material 2, and slow release of cold, the peak utilization of cold energy can be achieved, and 24-hour uninterrupted temperature control can be realized.

[0033] Furthermore, the phase change material 2 is one or more combinations of organic alkanes, polyols, inorganic eutectic salts, or brine systems. This type of low-temperature phase change substrate is suitable for low-temperature operating environments, exhibits excellent chemical stability, is not easily volatilized or corroded by supporting components, and has sufficient latent heat of phase change, stable energy storage and release performance, and can be used in a long-term cycle.

[0034] Furthermore, the phase change material 2 has a phase change point of -10℃ to -20℃. The phase change material 2 primarily involves a liquid-to-solid phase change process; its main function is to rapidly receive the cold energy transferred by the working heat pipe 5 during short periods at night; then slowly absorb heat and cool the surrounding soil. The critical phase change point of the phase change material 2 is controlled within the low-temperature range of -20℃ to -10℃, allowing for smooth bidirectional reversible phase change between solid and liquid states within this temperature range. This material can efficiently receive the cold energy continuously transferred by the working heat pipe 5 during short periods of low-temperature conditions at night, storing the cold energy as latent heat; after the ambient temperature rises during the day, it slowly and steadily releases the stored cold energy to the surrounding environment, continuously achieving balanced heat dissipation and long-term cooling effects, effectively balancing the ambient temperature difference, and ensuring the operational stability of the low-temperature system.

[0035] Furthermore, such as Figure 2As shown, the volume expansion absorption unit 3 includes a shrink tube 31 and an expansion bladder 32. The shrink tube 31 is inserted into the filling cavity and is in contact with the phase change material 2. The expansion bladder 32 is located at the other end of the shrink tube 31 and outside the heat rod shell 1. The expansion bladder 32 and the shrink tube 31 form a closed cavity.

[0036] The volume expansion absorption unit 3 is mainly composed of two parts: a contraction tube 31 and an expansion bladder 32. One end of the contraction tube 31 extends through and is inserted into the filling cavity, with its outer wall in direct contact with the phase change material 2 filled within the cavity. This allows for real-time sensing of the volume expansion and contraction deformation of the phase change material due to temperature changes. The expansion bladder 32 is fixedly positioned at the other end of the contraction tube 31, away from the filling cavity, and is arranged entirely on the outer side of the heat pipe shell 1, avoiding internal space constraints. The contraction tube 31 and the expansion bladder 32 are interconnected and form a complete sealed cavity structure. A buffer space can be reserved inside the cavity. When the low-temperature phase change material 2 undergoes a solid-liquid phase change and experiences volume expansion and compression, the pressure can be transmitted to the contraction tube 31. The expansion bladder 32 then adaptively absorbs the volume increase through elastic deformation, thereby buffering the internal stress generated by the phase change expansion, preventing shell deformation and cracking under pressure, maintaining the overall sealing performance of the filling cavity, preventing leakage of the phase change medium, and ensuring long-term stable operation of the device.

[0037] Furthermore, the contraction tube 31 is a thin-walled metal tube or a plastic hose, and the expansion bladder 32 is a cuboid or elliptical structure made of metal or plastic.

[0038] The shrink tube 31 is made of thin-walled metal tube or flexible plastic hose, which has excellent deformation adaptability and low temperature resistance. The tube wall thickness is uniform and the flexibility is moderate. It can undergo slight expansion and contraction deformation in response to pressure changes in the cavity. It can sensitively respond to volume fluctuations of phase change material 2. At the same time, it is corrosion resistant and anti-aging, and can be adapted to low temperature closed working conditions for a long time, avoiding low temperature brittleness and media erosion.

[0039] The expansion bladder 32 is made of metal or engineering plastic and features a closed rectangular or elliptical structure with excellent structural mechanical properties, strong pressure resistance, and stable deformation rebound. The rectangular shape is regular and compact, facilitating external placement and installation positioning, while the elliptical structure provides uniform stress distribution, effectively avoiding localized stress concentration. Both component materials are resistant to low temperatures and have good sealing properties. They are interconnected to form a sealed buffer cavity, which can stably absorb the volume expansion generated during the solid-liquid phase change of the phase change material by relying on its own deformation space, buffering internal extrusion pressure, and improving the overall structural adaptability and service life. Furthermore, such as Figure 3As shown, the working heat rod 5 includes an evaporation section 53 and a condensation section 51. The evaporation section 53 is inserted into the filling cavity; the condensation section 51 is located at one end of the evaporation section 53 and at the upper part of the heat rod shell 1; wherein, the outer surfaces of the evaporation section 53 and the condensation section 51 are respectively provided with multiple fins along the axial direction.

[0040] In this embodiment, the evaporation section 53 extends into and is fixed inside the filling cavity, completely submerged in or attached to the phase change material 2, and can fully contact the low-temperature phase change medium; the condensation section 51 is connected to the upper end of the evaporation section 53 and is exposed in the external environment of the heat rod shell 1 for heat exchange with the outside air.

[0041] Both the evaporation section 53 and the condensation section 51 have several arrayed fin structures uniformly arranged along the axial direction on their outer surfaces. The evaporation section 53 is equipped with evaporation section fins 54, and the condensation section 51 is equipped with condensation section fins 52. By expanding the heat exchange area and enhancing the convective heat transfer efficiency through the fins, the conduction and migration of cold and hot energy are accelerated.

[0042] In this embodiment, evaporation section fins 54 are integrated on the outer side of evaporation section 53, which can significantly increase the contact area between evaporation section and phase change material, quickly absorb the cold energy stored in phase change material, and improve the heat exchange rate. Condensation section fins 52 are correspondingly arranged on the outer side of condensation section 51, which can increase the heat dissipation contact surface between condensation section and external atmosphere, accelerate heat dissipation, and enhance heat exchange cycle. The segmented fin layout is specifically adapted to the heat exchange requirements of different operating conditions, effectively reducing thermal resistance, improving the overall heat conduction and cooling efficiency of working heat pipes, and ensuring continuous and stable operation of the system.

[0043] Firstly, regarding phase change heat absorption, the phase change material 2 placed around the evaporation section 53 of the working heat rod 5 can store a large amount of cold energy through the latent heat of the phase change process from liquid to solid; and the large-area contact between the fins of the working heat rod 5 and the phase change material 2 allows for rapid heat transfer. Thus, through the combination of these two factors, the pulsed cold energy transferred by the heat rod at night can be absorbed quickly and efficiently.

[0044] Secondly, in terms of intermittent and relay heat transfer, the cooled phase change material 2 continues to cool the surrounding permafrost as a cold source.

[0045] Third, regarding long-term cooling, since the accumulated cold energy of phase change material 2 is always present, it absorbs a large amount of heat from the surrounding environment through the solid-to-liquid phase change process. This allows for long-term, long-term cooling of the surrounding permafrost, enabling the heat pipe to operate for the vast majority of the time, even 24 hours a day, thus providing 24-hour cooling of the permafrost. Consequently, the operating time of the heat pipe can be significantly increased, greatly improving the cooling effect on the surrounding permafrost.

[0046] Furthermore, the condensation section 51 includes at least two branch structures.

[0047] The condensing section 51 is provided with at least two or more branch structures, with multiple branches extending in a parallel and bifurcated manner. Compared with the single-section structure, the branch design can significantly broaden the coverage of condensing heat exchange, effectively increase the overall surface heat exchange area of ​​the condensing section, and enhance the convective heat exchange and radiative heat dissipation effect with the external environment.

[0048] Meanwhile, the multi-branch structure can distribute the heat exchange load, avoid the problems of concentrated heat exchange and uneven heat dissipation in a single pipeline, effectively reduce local thermal resistance, accelerate the condensation and reflux rate of the internal working fluid, and ensure smooth gas-liquid phase change circulation inside the working heat rod.

[0049] The evaporation section 53 features an integrally formed V-shaped structure at its end to connect the two branch structures. The working heat pipe 5 is essentially the same as a conventional heat pipe, but both the condensation section 51 and the evaporation section 53 have fins. Furthermore, to increase heat dissipation efficiency, the condensation section 51 has a V-shaped structure, which significantly increases the efficiency of heat dissipation and the heat pipe itself. The V-shaped structure of the condensation section 51 not only improves efficiency but also prevents the working heat pipe 5 from bending due to its thinness. Its length ranges from 1.5m to 3.0m.

[0050] The outer diameter of the evaporation section 53 is 30% to 60% of the inner diameter of the heat pipe shell 1.

[0051] The diameter of the working heat pipe 5 is 30% to 60% of the inner diameter of the original failed heat pipe, thus achieving optimal heat transfer with the phase change material 2. The working heat pipe 5 adopts a Y-shaped structure, which not only significantly increases the heat dissipation area but also effectively avoids the problem of easy bending of small-diameter heat pipes. At the same time, fins are distributed in both the evaporation section 53 and the condensation section 51, further improving the heat exchange efficiency. The shrinkage unit can adapt to the volume changes of the phase change material 2, eliminating the structural damage to the original heat pipe metal tube caused by its freeze-thaw expansion and contraction, and ensuring the long-term stable operation of the device under extreme freeze-thaw cycle environments.

[0052] This invention also proposes a method for repairing failed permafrost heat pipes, comprising the following steps: Step S101: Cut off the failed frozen soil heat pipe and leave the part buried underground as the heat pipe shell 1; Step S103: Insert the working heating rod and the body expansion absorption unit into the filling cavity respectively; Step S105: Fill the filling cavity of the heat pipe shell with phase change material; Step S107: The upper end of the buried part is sealed with a sealing element, so that the lower end of the working heat rod passes through the sealing element and is coaxially inserted into the filling cavity, and the upper end of the working heat rod is located above the sealing element; the lower end of the volume expansion absorption unit passes through the sealing element but is not coaxially inserted into the filling cavity, so as to absorb the volume change of the phase change material during the phase change process through its own volume expansion and contraction, and the upper end of the volume expansion absorption unit extends out of the sealing element and is located outside the heat rod shell.

[0053] In this embodiment, for the discovered and confirmed failed heat pipes, the metal tube of the heat pipe is cut off at a height of 10-30cm above the ground surface, while the lower part of the heat pipe metal tube is retained.

[0054] The pipe openings of the remaining heat pipes are ground and smoothed. If necessary, the pipe openings can be pre-treated by wire drawing or welding. The remaining underground metal pipes are cleaned and dried. New working heat pipes 5 are implanted and inserted, and the body expansion absorption unit 3 is inserted simultaneously. At the same time, the expansion bladder 32 of the shrinkage unit is buried in shallow soil. The prepared phase change material 2 is poured in and filled. The original heat pipe openings are sealed with sealing components 4.

[0055] The sealing element can be a threaded sealing cap. The sealing element is a split-type threaded sealing cap, comprising two symmetrically arranged half-caps and a threaded fastening sleeve. Each half-cap has a semi-circular groove for the working heat pipe and the expansion absorption unit to fit together. After the two half-caps are joined from the side of the working heat pipe, they are locked in place by the threaded fastening sleeve. The fastening sleeve has internal threads to hold the two half-caps together and simultaneously engages with the external threads of the heat pipe's outer casing. Low-temperature resistant sealant is used to fill the joints, threaded connections, and gaps between the pipe and the semi-circular grooves.

[0056] During sealing, the two half-covers can be pre-assembled from the left and right sides of the working hot rod straight pipe section to wrap around the straight pipe section. The sides of the half-covers also wrap around the body expansion absorption unit to complete the positioning. Then, tighten the outer threaded fastening sleeve to hold and fix the split cover. Finally, fill all the threaded joints, the splicing gaps of the half-covers, and the gaps between the pipe and the tank with low-temperature resistant sealant to achieve a complete seal.

[0057] Of course, sealing elements can also be achieved using flange welding or clamp sealing, which will not be elaborated upon here.

[0058] Addressing the challenges of excavating failed heat pipes in permafrost regions, the high cost of replacement, and the potential engineering hazards posed by their abandonment, this device eliminates the need for complete removal of the failed heat pipe. Instead, it involves a simple truncation of the surface section, utilizing the existing metal casing as a carrier to implant the working heat pipe 5, phase change material 2, and shrinkage unit, thus completing the repair. This approach preserves the fundamental structural value of the failed heat pipe while avoiding secondary damage to the permafrost subgrade and surrounding ecosystem caused by large-scale excavation, effectively solving the industry-wide problem of handling failed heat pipes in permafrost engineering.

[0059] In addition, the repair process of the device only requires surface cutting of the failed heat pipe, internal cleaning, component implantation, phase change material injection and sealing treatment. No large construction equipment is required throughout the process. The construction steps are simple and convenient to operate. It can be quickly implemented on the site of existing permafrost projects such as the Qinghai-Tibet Highway and Qinghai-Tibet Railway. It is suitable for repairing failed heat pipes of different specifications in various permafrost projects such as highways, railways, bridges, and power transmission towers. The construction has little interference and a short construction period.

[0060] Compared to the traditional method of replacing the entire failed heat pipe, this invention only requires the replacement of core components such as the working heat pipe 5 and the phase change material 2, significantly reducing the costs of material procurement, engineering excavation, transportation, and installation, and substantially lowering the operation and maintenance investment for permafrost projects. Simultaneously, the construction process involves no large-scale earthwork, avoiding damage to surface vegetation and soil structure in permafrost areas. Furthermore, the device poses no risk of working fluid leakage throughout the entire process, preventing pollution of surrounding soil and water bodies. This approach balances engineering benefits with ecological protection, meeting the development requirements for green operation and maintenance in permafrost regions.

[0061] This invention, through its continuous and stable cooling effect, can effectively maintain the frozen state of permafrost, increase the upper limit of permafrost, increase the thickness of the permafrost layer, and ensure the bearing capacity and shear strength of permafrost. It can fundamentally alleviate engineering problems such as frost heave and thaw settlement of roadbeds and settlement and tilting of foundations of structures, reduce the frequency of engineering maintenance, extend the service life of permafrost projects, and provide continuous protection for the long-term safe operation of transportation, energy and other infrastructure in permafrost areas.

[0062] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A frozen soil heat pipe, characterized in that, include: The outer shell of the heat pipe has a filling cavity and a sealing element at the upper opening, wherein the filling cavity is filled with a phase change material; The working heating rod has its lower end passing through the seal and coaxially inserted into the filling cavity, with its upper end located above the seal. The volume expansion absorption unit is an elastically expandable strip structure. The lower end of the volume expansion absorption unit passes through the seal and is not coaxially inserted into the filling cavity, so as to absorb the volume change of the phase change material during the phase change process through its own volume expansion and contraction. The upper end of the volume expansion absorption unit extends out of the seal and is located outside the heat rod shell.

2. The frozen soil heat pipe according to claim 1, characterized in that, The phase change material is one or more combinations of organic alkanes, polyols, inorganic eutectic salts, or brine systems.

3. The permafrost heat pipe according to claim 1, characterized in that, The phase change material has a phase change point of -10℃ to -20℃.

4. The permafrost heat pipe according to claim 1, characterized in that, The volume expansion absorption unit includes: A shrink tube is inserted into the filling cavity and comes into contact with the phase change material; An expansion bladder is located at the other end of the contraction tube and outside the outer shell of the heat rod, forming a closed cavity with the contraction tube.

5. The permafrost heat pipe according to claim 4, characterized in that, The contraction tube is a thin-walled metal tube or a plastic flexible tube, and the expansion bladder is a cuboid or elliptical structure made of metal or plastic.

6. The frozen soil heat pipe according to any one of claims 1 to 5, characterized in that, The working heat pipe includes: The evaporation section is inserted into the filling cavity; A condensation section is located at one end of the evaporation section and at the upper part of the heat pipe shell; The outer surfaces of the evaporation section and the condensation section are respectively provided with multiple fins along the axial direction.

7. The frozen soil heat pipe according to claim 6, characterized in that, The condensation section includes at least two branch structures.

8. The frozen soil heat pipe according to claim 7, characterized in that, The end of the evaporation section is integrally formed with a V-shaped structure to connect the two branch structures.

9. The permafrost heat pipe according to claim 6, characterized in that, The outer diameter of the evaporation section is 30% to 60% of the inner diameter of the heat pipe shell.

10. A method for repairing a failed permafrost heat pipe, characterized in that, include: The failed permafrost heat pipe is cut off, leaving the part buried underground as the outer shell of the heat pipe; A working heating rod and a body expansion absorption unit are respectively inserted into the filling cavity; A phase change material is filled into the filling cavity of the heat pipe shell; The upper end of the buried part is sealed with a sealant, so that the lower end of the working heat rod passes through the sealant and is coaxially inserted into the filling cavity, and the upper end of the working heat rod is located above the sealant; the lower end of the volume expansion absorption unit passes through the sealant but is not coaxially inserted into the filling cavity, so as to absorb the volume change of the phase change material during the phase change process through its own volume expansion and contraction, and the upper end of the volume expansion absorption unit extends out of the sealant and is located outside the heat rod shell.

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