Enhanced hot rod for protecting permafrost

Abstract

The invention discloses an enhanced thermal rod for protecting permafrost, which belongs to the technical field of permafrost protection, and comprises a gravity thermal rod unit, a loop heat pipe bundling unit and a radiation refrigeration unit, the gravity thermal rod unit is a thermal rod filled with a heat transfer working medium, and is divided into a condensation section, a heat insulation section and an evaporation section from top to bottom in sequence; the two layers are respectively positioned above the ground, on an active layer and on a permafrost layer; the loop heat pipe bundling unit comprises a plurality of loop heat pipes radially arranged around the hot rod, the loop heat pipes formed by sequentially connecting an evaporator, a gas pipeline, a condenser and a liquid pipeline are filled with nano fluid working media, the evaporator and the liquid pipeline are arranged inside the hot rod, and the condenser and the gas pipeline are arranged outside the hot rod; and the radiation refrigeration unit is coated outside the condensation section and the condenser corresponding to the condensation section. The gravity heat rod is combined with the loop heat pipe technology and the radiation refrigeration technology, the internal heat resistance of the heat rod can be reduced, the external cold energy capturing capacity is improved, and cooling protection of permafrost is achieved.

Description

Technical Field

[0001] This invention belongs to the field of permafrost protection technology, and specifically relates to an enhanced heat pipe for protecting permafrost. Background Technology

[0002] Under conditions of global warming, permafrost is showing a trend of warming and degradation, and its melting, settlement, and deformation pose a significant threat to infrastructure such as buildings, power tower foundations, oil pipelines, and transportation structures. Therefore, how to cool and protect permafrost and maintain its thermal stability is a major challenge facing engineering construction and operation in permafrost regions. Especially when foundation damage extends to infrastructure, efficient and rapid cooling protection is required. Currently, heat pipes are the primary cooling measure for permafrost. Essentially, they are enlarged coreless gravity heat pipes filled with liquid ammonia. The evaporation section is placed below the permafrost layer, and the condensation section is placed above the ground in the air. When the air temperature is lower than the permafrost temperature, the liquid working fluid in the evaporation section absorbs heat, vaporizes, and rises to the condensation section. After dissipating heat and liquefying in the condensation section, it flows back to the evaporation section by gravity, thus cyclically absorbing heat from the permafrost foundation. It is evident that the circulation power of gravity heat pipes mainly relies on the buoyancy of the gas and the gravity of the liquid, and its advantage is that it is passively driven and consumes zero energy.

[0003] Many years of application show that the hot stick mainly has the following defects: (1) carrying limit. In order to meet the one-way heat dissipation requirement of permafrost, compared with the conventional heat pipe, the first change of the hot stick is to cancel the capillary liquid core, see "hot stick and hot stick type pipe rack" (GB / T 27880). This leads to the fact that the hot stick cannot be arranged horizontally and must be vertical or inclined, and the liquid phase working medium returns by gravity to maintain one-way heat conduction, and the evaporation heat absorption effect is concentrated in the lower part of the evaporation section. On the other hand, the gaseous and liquid working medium is in contact, which leads to the fact that when the ascending speed of the gaseous working medium in the hot stick is large enough, the shear force of the liquid-gas interface will slow down the return speed of the liquid working medium, and even the liquid working medium will be wrapped into the gas flow, thereby reducing the working medium return amount. When the entrainment is serious, it will cause the evaporation section to dry up, that is, the carrying heat transfer limit is formed, which leads to the defects of low working medium circulation efficiency and poor evaporation section uniformity. (2) Starting limit. In order to meet the heat dissipation efficiency and temperature reduction requirement of permafrost, compared with the conventional heat pipe, the second change of the permafrost hot stick is to enlarge the structure size, the working medium filling amount is increased, and the migration pressure drop is also increased. Due to the low phase change activity of the working medium, combined with the small pressure difference between the condensation section and the evaporation section in the hot stick, therefore, only when the atmospheric temperature is greatly reduced to a certain threshold (generally about 5 DEG C) higher than the temperature difference between the permafrost, the working medium can start phase change heat transfer. The hot stick is usually in a fluctuating operation state from the middle of October to the middle of March of the next year, which leads to the defects of large hot stick starting temperature difference and short effective operation time. (3) Condensation limit. The outer wall of the hot stick adopts conventional metal material spiral blade, and the heat dissipation efficiency is restricted by air temperature and wind speed, and the natural cold energy capturing capacity is insufficient, and the maximum heat transfer capacity is limited by the condensation capacity, which leads to the fact that the hot stick cannot maintain stable heat transfer power. Moreover, in the warm season, the metal pipe material is easy to heat up under solar radiation, and the heat is transferred to the permafrost layer. The above defects lead to the fact that the cooling range and influence range of the hot stick are small, and the effective cooling radius of the hot stick is usually only about 1.5 m, which is easy to cause differential deformation. Especially on the Qinghai-Tibet Highway, due to the insufficient cooling efficiency of the hot stick in winter, combined with the heat accumulation effect in the warm season, a chain reaction of heat runaway is easily triggered, which leads to serious longitudinal cracking of the highway. Under the background of continuous expansion of infrastructure construction scale and quality improvement of existing facilities in the Qinghai-Tibet Plateau, the optimization and improvement of the hot stick are imminent. SUMMARY

[0004] The purpose of the present application is to provide an enhanced hot stick for protecting permafrost, which aims to solve the technical problems of the carrying limit, the starting limit and the condensation limit of the existing permafrost hot stick.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: The application discloses an enhanced heat rod for protecting permafrost, which comprises a gravity heat rod unit, a loop heat pipe cluster unit and a radiation refrigeration unit. The loop heat pipe cluster unit comprises a plurality of loop heat pipes which are sequentially connected by an evaporator, a gas pipeline, a condenser and a liquid pipeline. The radiation refrigeration unit is coated on the outer part of the condenser of the loop heat pipe corresponding to the condenser of the heat rod.

[0006] Preferably, the heat rod is a sealed hollow pipe which is filled with heat transfer working medium and has a vacuum cavity.

[0007] Further, the heat transfer working medium filled in the heat rod is liquid ammonia, and the phase transition critical temperature of the phase change energy storage material is between the gasification heat absorption temperature of the heat transfer working medium and the temperature threshold corresponding to the stable state of the permafrost.

[0008] Further, the outer wall of the condenser is provided with a spiral spoiler.

[0009] Further, the spiral spoiler is an aluminum alloy plate which is spirally wound on the outer part of the condenser.

[0010] Further, the upper and lower ends of the loop heat pipe are respectively a U-shaped bend I and a U-shaped bend II. The curvature radius of the U-shaped bend I is 50 mm, the pipe diameter is 20 mm, the pipe wall thickness is 1 mm and the inner diameter is 18 mm.

[0011] Preferably, the evaporator is divided into two sections, the lower section is a plurality of parallel capillary bundles, the upper section is a straight-through pipe, and a capillary core is installed on the inner wall of the capillary bundle.

[0012] Further, the evaporators and condensers of a plurality of loop heat pipes are connected in parallel, the evaporators and liquid pipes of the plurality of loop heat pipes are connected through a liquid reservoir, the outlet of the liquid pipe is connected to the top of the liquid reservoir, and the inlet of the evaporator is connected to the bottom of the liquid reservoir.

[0013] Further, the nanofluid working medium selects a nanomagnetic fluid, and the nanoparticles in the nanomagnetic fluid are nanoscale metal or metal oxide particles. The inside of the heat rod is provided with a float valve, the top of the float valve is provided with a permanent magnet, and the permanent magnet and the float valve are arranged at the lower part of the capillary bundle of the evaporator and can change with the rise and fall of the liquid ammonia level at the bottom of the heat rod.

[0014] Further, the radiation refrigeration unit is a dielectric / polymer composite radiation refrigeration film with a 3D porous structure.

[0015] Compared with the prior art, the technical progress achieved by the present application is that: The present application combines the gravity heat rod with the loop heat pipe technology and the radiation refrigeration technology, separates the gas pipe and the liquid pipe of the loop heat pipe, reduces the flow resistance of the internal heat transfer working medium of the heat rod, improves the phase change efficiency of the internal heat transfer working medium, and improves the external cold energy capture capacity of the heat rod, thereby realizing the cooling protection of permafrost. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, illustrate the present application together with the embodiments thereof, and explain the present application, but do not constitute a limitation of the present application.

[0017] In the drawings: Figure 1 An external shape of an enhanced heat rod for protecting permafrost is provided for the embodiments of the present application. Figure 2 For Figure 1The scene schematic diagram of the enhanced heat rod applied to the railway subgrade; Figure 3 For Figure 2 The section schematic diagram of the railway subgrade; Figure 4 The structure schematic diagram of the heat rod in the embodiment of the present application; Figure 5 The structure schematic diagram of the loop heat pipe in the embodiment of the present application; Figure 6 The arrangement schematic diagram of the several loop heat pipes in the embodiment of the present application; Figure 7 The structure schematic diagram of the combination of the heat rod and the loop heat pipe in the embodiment of the present application; Figure 8 For Figure 1 The cooperation schematic diagram of the upper spiral spoiler and the condenser of the enhanced heat rod; Figure 9 The structure schematic diagram of the lower part of the enhanced heat rod in the embodiment of the present application; Figure 10 For Figure 9 The cooperation schematic diagram of the liquid accumulator and the loop heat pipe; Figure 11 For Figure 9 The cooperation schematic diagram of the permanent magnet, the float valve and the loop heat pipe; In the figure: 100-heat rod, 101-condensing section, 102-heat insulation section, 103-evaporating section, 104-liquid ammonia; 105-threaded end cap, 106-spiral spoiler, 107-heat preservation sleeve, 108-phase change energy storage sleeve; 400-loop heat pipe, 401-straight-through pipe, 402-capillary tube bundle, 403-gas pipeline, 404-condenser, 405-liquid pipeline, 406-U-shaped bend I, 407-U-shaped bend II; 5-liquid accumulator; 6-nanofluid working medium; 7-permanent magnet; 8-float valve; 9-active layer of foundation; 10-permafrost layer; 11-subgrade. DETAILED DESCRIPTION

[0018] The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present application will be described below with reference to the accompanying drawings.

[0019] In view of the problems of carrying limit, starting limit and condensation limit of the current permafrost heat rod, the optimization means of the heat rod are mostly from the external structure aspects such as liquid filling rate and inclination angle, but the essence of the heat rod work is heat transfer based on the phase change of the working medium, and the optimization effect is limited. Therefore, in recent years, the industry has introduced active refrigeration technology to improve the performance of the heat rod. For example, the application number CN202311599322.8 discloses a full-time heat rod system, which adds a power-driven semiconductor refrigeration piece on the condensation section of the heat rod, which eliminates the operation empty period in the warm season, but needs to additionally increase external power supply supporting equipment, has the limitations of high energy consumption, high investment and unreliable durability, is mainly suitable for scenes with serious heat melting diseases and emergency disposal, and is difficult to popularize on a large scale.

[0020] In general, the heat rod is still the main measure for permafrost protection in the future due to its technical advantages of zero energy consumption, natural cold energy utilization and high phase change heat carrying efficiency. In view of the technical limitations of the active driven refrigeration component, it is the key to improve the heat transfer performance of the heat rod body to improve the technical level of permafrost protection.

[0021] As shown in Figure 1 , Figure 2 and Figure 3 , the enhanced heat rod for protecting permafrost provided by the embodiment of the present application comprises a gravity heat rod unit, a loop heat pipe cluster unit and a radiation refrigeration unit. The gravity heat rod unit is a cylindrical heat rod 100 filled with heat transfer working medium inside. The heat rod 100 is sequentially divided into a condensation section 101, an adiabatic section 102 and an evaporation section 103 from top to bottom. The adiabatic section 102 and the evaporation section 103 are inserted into the permafrost, the condensation section 101 extends above the ground, the length of the adiabatic section 102 is consistent with the thickness of the active layer 9 of the foundation, and the length of the evaporation section 103 is consistent with the warming degradation depth in the permafrost layer 10. The heat transfer working medium filled in the heat rod is liquid ammonia 104. The normal pressure boiling point of the liquid ammonia is -33.5℃, which is much lower than the temperature of the permafrost layer. First, the liquid ammonia will absorb heat and evaporate into gas when it is in the evaporation section, realizing the cooling and protection effect on the permafrost around the pipe; then, the ammonia gas flows to the upper condensation section under a small pressure difference, and releases heat when it condenses in the condensation section; then, the condensed liquid flows back to the evaporation section by gravity, completing the whole cycle. The loop heat pipe cluster unit comprises a plurality of loop heat pipes 400, which are sequentially connected by an evaporator (consisting of a straight-through pipe 401 and a capillary pipe cluster 402), a gas pipe 403, a condenser 404, and a liquid pipe 405. The inside of the loop heat pipe 400 is a fluid loop filled with nanofluid working medium 6. The plurality of loop heat pipes 400 are radially arranged around the periphery of the heat rod 100 with the central axis of the heat rod 100 as the center. The evaporator and the liquid pipe 405 are arranged inside the heat rod 100, and the condenser 404 and the gas pipe 403 are arranged outside the heat rod 100. The radiation cooling unit is coated on the outside of the condensing section 101 of the heat rod 100 and the outside of the condenser 404 corresponding to the height range of the condensing section 101.

[0022] The working principle of the enhanced heat rod is as follows: taking the gravity heat rod unit as the main body, the loop heat pipe and the radiation cooling unit are used to optimize and improve the cooling protection effect of permafrost. Specifically, a plurality of loop heat pipes are radially arranged around the heat rod, and the evaporator and the liquid pipe of the loop heat pipe are arranged inside the heat rod, and the condenser and the gas pipe are arranged outside the heat rod. The gas pipe and the liquid pipe of the loop heat pipe are designed to be separated to focus on improving the carrying limit and starting limit of the gravity heat rod unit. The radiation cooling unit is coated on the outside of the condensing section of the heat rod and the outside of the condenser corresponding to the height range of the condensing section to focus on improving the condensing limit of the gravity heat rod unit.

[0023] As a preferred structure, as shown in Figure 4 The heat rod 100 is a sealed hollow pipe, and the top end and the bottom end of the pipe are threaded end caps 105. The inside of the heat rod 100 is filled with liquid ammonia 104, and the cavity part is in a vacuum state. The loop heat pipe 400 is provided with a heat preservation sleeve 107 and a phase change energy storage sleeve 108. The heat preservation sleeve 107 corresponds to the heat insulation section 102 of the heat rod 100. The phase change energy storage sleeve 108 corresponds to the evaporation section 103 of the heat rod 100, and the inside of the phase change energy storage sleeve 108 is filled with phase change energy storage material. The phase change critical temperature of the phase change energy storage material should be between the gasification heat absorption temperature of the liquid ammonia 104 and the temperature threshold corresponding to the stable state of the permafrost.

[0024] In specific production, the heat rod 100 is produced according to the requirements of “Heat Rod and Heat Rod Type Pipe Rack” (GB / T 27880) for material selection, size design and production. The material of the heat rod 100 pipe is carbon steel, the outer diameter is 89 mm, the wall thickness is 2 mm, and the inner diameter is 85 mm. The height of the condensing section 101 is set to 2.0-4.0 m. Generally, the heights of the condensing section 101, the heat insulation section 102, and the evaporation section 103 of the heat rod 100 are set to 3.0 m, 2.0 m, and 4.0 m, respectively. The filling mass of the liquid ammonia 104 is 2500 g.

[0025] Preferably, the critical temperature value of the phase change energy storage material is determined according to the relevant standards or specifications corresponding to the application scenario. For example, when applied to permafrost protection of highway engineering, according to the provisions of the Technical Code for Design and Construction of Highway in Permafrost Regions (JTG / T 3331-04), the temperature threshold corresponding to the stable state of permafrost is-3.0℃, and the critical temperature of the phase change energy storage material should be lower than-3℃. The purpose is to overcome the defects of low specific heat capacity and low thermal conductivity of permafrost, and to improve the heat exchange amount when the heat rod starts to transfer heat in low temperature and severe cold weather, which can prevent the temperature of the outer wall of the evaporation section from being too low to cause cold accumulation and cold energy diffusion not timely, and can store energy and maintain appropriate temperature gradient, which is beneficial to improve the continuity of cold diffusion and effective cold output. At the same time, the outer sleeve of the phase change energy storage material is made of stainless steel pipe to protect the internal material from deformation and damage of the foundation.

[0026] In specific production, the phase change energy storage material uses ammonium nitrate (NH4NO3) dissolved in crystalline hydrated salt, and its phase change temperature is controlled at-5~ -10℃, which is between the evaporation temperature of liquid ammonia in the heat rod and the low temperature stable threshold of permafrost. Its beneficial effect is to improve the mismatch between the short operation time of the heat rod and the poor thermal conductivity of permafrost, and to realize continuous heat absorption of permafrost and rapid heat release of the heat rod through its high thermal conductivity and large specific heat capacity, that is, to realize cascade cold storage and optimize the cooling effect of the heat rod on permafrost.

[0027] At the same time, the heat preservation sleeve 107 adopts an elastic plastic heat preservation pipe which can adapt to low temperature and water-rich conditions, and the height of the heat insulation section corresponds to the thickness of the active layer of permafrost foundation, so as to prevent the condensed section from absorbing heat and gasifying in the heat insulation section, and to avoid affecting the evaporation rate of the evaporation section and the protection effect of permafrost. At the same time, the elastic plastic heat preservation pipe is sleeved with a stainless steel pipe to protect the internal material from deformation and damage of the foundation. In production, the thickness of the heat preservation sleeve and the phase change energy storage sleeve is 40mm, which is convenient for drilling and implantation with a standard specification drill bit (diameter 175mm) of a conventional drilling machine, ensures that the pipe body is closely attached to the stratum, ensures the heat transfer efficiency between the interfaces, and prevents surface water from seeping in.

[0028] Further optimize the above structure, such as Figure 4As shown, the outer wall of the condensing section 101 is provided with a spiral spoiler 106, and the condenser 404 of the loop heat pipe 400 penetrates the spiral spoiler 106 from top to bottom. The spiral spoiler 106 is a wavy aluminum alloy plate with a width of 40 mm and a spiral pitch of 10 cm, and a circular hole with a diameter of 3 mm is drilled in the aluminum alloy plate. The spiral spoiler can increase the heat exchange area, enhance the induction and turbulence of the air, and form a turbulent flow on the outer wall of the condensing section. Compared with the spiral heat dissipation blades on the outer wall of the traditional heat rod, the turbulent flow makes the air contact with the condensing section for a longer time, and can capture more cold energy under the same air temperature and flow rate conditions.

[0029] In a specific embodiment of the present application, as shown in Figure 5 、 6 The upper and lower ends of the loop heat pipe 400 are respectively a U-shaped bend I 406 and a U-shaped bend II 407. The two ends of the U-shaped bend I 406 are respectively connected with the condenser 404 and the liquid pipeline 405, forming a condensing end U-shaped pipe. The two ends of the U-shaped bend II 407 are respectively connected with the evaporator and the gas pipeline 403, forming an evaporating end U-shaped pipe. The evaporator and the condenser respectively play the roles of heat absorption and heat dissipation, i.e. absorbing the heat of permafrost to cool it down and dissipating the heat to the outside. The condenser 403 is connected with the spiral spoiler 106 on the outer wall of the condensing section 101 of the gravity heat rod unit, which helps to increase the heat exchange area of the condenser 403 and the surrounding atmosphere and improve the heat exchange efficiency.

[0030] As a preferred structure, as shown in Figure 5 The evaporator is divided into two sections, the lower section is a plurality of parallel capillary tube bundles 402, and the upper section is a straight-through pipe 401. The inner wall of the capillary tube bundle 402 is provided with a capillary core, which provides capillary power for the migration of the nanofluid working medium 6. The capillary core is made of a mixture of metal fibers and ceramic whiskers, and has the following performance specifications: average pore size <1 μm (0.8-1.2 μm accounts for >95%), open porosity >70%, equivalent thermal conductivity <3 W / (m·K), and compressive strength >50 MPa. The capillary core 405 is arranged inside the evaporator 401. The capillary core provides capillary driving force for the migration of the liquid nanofluid working medium 6, so that it flows uniformly and evaporates in the height range of the capillary tube bundle 402 to produce a cooling effect. The beneficial effects brought by this are as follows: First, the carrying limit problem of the evaporation section 103 of the heat rod 100 is improved, and the liquid ammonia 104 in the condensation section 101 is prevented from being affected by the overheat gas flow of the liquid ammonia 104 in the upper part of the adiabatic section 102 and the evaporation section 103 during the gravity backflow process after condensation; second, when the gasification heat absorption effect of the liquid ammonia 104 in the heat rod 100 is limited to the bottom of the evaporation section 103, or when the heat transfer cannot be transmitted due to the start limit, the loop heat pipe 400 can still work normally with the assistance of the capillary core 405, thereby improving the start limit problem of the heat rod 100 and the uniformity of heat absorption and cooling; third, the anti-gravity capability is improved, and the limitation that the traditional heat rod 100 can only be vertically arranged and arranged at a large inclination angle is overcome, so that the loop heat pipe can stably operate at any installation position.

[0031] In the specific design, the size of the straight-through pipe 401 is: a pipe diameter of 30 mm, a wall thickness of 1 mm, an inner diameter of 28 mm, and a height of 2.0 m, which corresponds to the range of the adiabatic section 101 of the gravity heat rod unit, and the purpose is to reduce the flow resistance and gasification heat absorption rate of the nanofluid working medium. The size of the capillary tube bundle 402 is: a pipe diameter of 6 mm, a wall thickness of 1 mm, an inner diameter of 4 mm, and a height of 4.0 m, which corresponds to the range of the evaporation section 103 of the gravity heat rod unit, and the purpose is to increase the gasification heat absorption rate of the nanofluid working medium.

[0032] The condenser 404 is a copper pipe with a fixed pipe diameter, a pipe diameter of 20 mm, a wall thickness of 1 mm, an inner diameter of 18 mm, and a height of 5.0 m. The purpose of the condenser pipe diameter (20 mm) being lower than the evaporator pipe diameter (30 mm) is to create differences in the flow speed and environmental pressure of the nanofluid working medium 6 inside the condenser and the evaporator under the same circulation flow rate, to improve the pressure difference, to meet the nanofluid working medium circulation requirements of low-pressure environment for evaporation heat absorption and high-pressure environment for condensation heat dissipation, thereby reducing the start-up temperature difference required for the nanofluid working medium phase change cycle to overcome the start-up limit of the existing heat rod.

[0033] The gas pipeline 403 is a copper pipe with a gradually changing diameter, the pipe diameter decreases from 30 mm to 20 mm, the wall thickness is 1 mm, and the height is 4.0 m. The diameter gradually decreases along the gas flow direction, and the purpose is to increase the moving speed of the gaseous nanofluid working medium, overcome the influence of gravity, and ensure that the gaseous nanofluid working medium can spontaneously migrate upward into the condenser.

[0034] The liquid pipeline 405 is a copper pipe with a gradually changing diameter, the pipe diameter increases from 20 mm to 30 mm, the wall thickness is 1 mm, and the height is 3.0 m. The diameter gradually expands along the liquid flow direction, and the purpose is to improve the backflow efficiency of the liquid nanofluid working medium, so that the liquid droplets can overcome the influence of the pipe wall flow resistance after being collected and quickly flow downward or drop, thereby ensuring that the nanofluid working medium can quickly backflow and directly drop after condensation, return to the evaporator, and promote the nanofluid working medium circulation.

[0035] The loop heat pipe is made as follows: firstly, the condenser 404 is connected with the liquid pipeline 405 to form a condensing end U-shaped pipe through a U-shaped bend I with a curvature radius of 50 mm, a pipe diameter of 20 mm, a pipe wall thickness of 1 mm and an inner diameter of 18 mm; then, the evaporator capillary bundle 402 is connected with the gas pipeline 403 to form an evaporating end U-shaped pipe through a U-shaped bend II with a curvature radius of 50 mm, a pipe diameter of 30 mm, a pipe wall thickness of 1 mm and an inner diameter of 28 mm; then, the evaporating end U-shaped pipe is connected with the condensing end U-shaped pipe to form a closed loop, wherein the inlet of the straight-through pipe 401 of the evaporator is connected with the outlet of the liquid pipeline 405, and the outlet of the gas pipeline 403 is connected with the inlet of the condenser 404, that is, the two U-shaped pipes are connected in an up-down manner to form a closed circulation loop.

[0036] The working principle of the loop heat pipe is as follows: firstly, when the capillary core inside the evaporator capillary bundle 402 flows into the liquid nanofluid working medium 6, the nanofluid working medium vaporizes due to the low boiling point temperature of the nanofluid working medium, a large amount of heat (latent heat) is absorbed in the phase change process, and a refrigeration effect is generated; secondly, the gaseous nanofluid working medium 6 moves upward in the vacuum environment due to its low density, is transported to the condenser 404 through the gas pipeline 403, and then condenses into a gas-liquid mixed state or a liquid state after releasing heat in the condenser 404, and enters the liquid pipeline 405; then, the liquid nanofluid working medium 6 moves downward through the liquid pipeline 405 under the action of gravity and returns to the straight-through pipe 401 of the evaporator; finally, the liquid nanofluid working medium 6 reenters the capillary core inside the capillary bundle 402 through the straight-through pipe 401 and covers the inner wall of the entire capillary bundle 402 under the action of capillary force, and continues to absorb heat and evaporate. Thus, the phase change process of the nanofluid working medium 6 is repeated, and efficient heat transfer is achieved. It can be seen that, compared with the gravity heat rod 100, the nanofluid working medium is driven to circulate by capillary force and gravity in the loop heat pipe 400.

[0037] It can be seen that, compared with the straight-through structure of the traditional heat rod 100, the closed circulation loop structure of the loop heat pipe 400 and the structure form in which the evaporation section 101 and the condensation section 103 are directly communicated are different, the gas pipeline 403 and the liquid pipeline 405 of the loop heat pipe 400 are relatively separated, and the entrainment effect caused by the contact between the upward airflow and the downward liquid flow in the circulation process of the nanofluid working medium 6 is avoided. At the same time, combined with the capillary core of the evaporator capillary bundle 402 and the special design of the gas pipeline 403 and the liquid pipeline 405 with gradually changing diameters, the entrainment limit defect is comprehensively improved.

[0038] In the specific embodiment of the present application, the structure of the loop heat pipe cluster unit is that the evaporators (consisting of straight-through pipes 401 and capillary pipe bundles 402) and condensers 404 of a plurality of loop heat pipes 400 are connected in parallel to operate; the outlets of the liquid pipes 405 of all loop heat pipes 400 are connected to the upper top surface of the liquid reservoir 5, and the inlets of the evaporators of all loop heat pipes 400 are connected to the lower bottom surface of the liquid reservoir 5. The loop heat pipes 400 are evenly distributed on the cylindrical liquid reservoir 5, and form a whole annular column structure. The beneficial effects of using the above loop heat pipe cluster unit are that each loop heat pipe operates independently and does not affect each other, and collectively shares the cooling load of permafrost, the circulating amount of the nanofluid working medium 6 is automatically and dynamically distributed according to the impedance of each branch, the overall impedance is reduced, the fault tolerance is high, and the capacity expansion is easy, etc.

[0039] In the specific implementation, the liquid reservoir 5 is a cylindrical storage tank with an inner diameter of 50 mm and a height of 100 m; the number of loop heat pipes 400 is 6, that is, the 6 loop heat pipes 400 are evenly distributed on the cylindrical storage tank at an angle of 60°.

[0040] In the specific embodiment of the present application, the nanofluid working medium 6 is selected as a nanomagnetic fluid, and the nanometer particles in the nanomagnetic fluid are nanometer metal or metal oxide particles. The nanofluid working medium is a new type of phase change heat carrier, which is a ternary suspension liquid composed of nanometer particles, base fluid and dispersant. The base fluid is selected as liquid ammonia, the dispersant is anhydrous methanol, and the concentration of liquid ammonia should be controlled between 23% and 27%, so as to ensure that the evaporation temperature of ammonia water is lower than the minimum temperature of permafrost. Compared with liquid ammonia 104, the nanofluid working medium 6 has a higher thermal conductivity, and can increase the active nucleation site through the particle effect of the nanometer particles deposited on the wall surface, which is a heat transfer enhancement technology. At the same time, the mass fraction of metal or metal oxide particles is 3.0%, which can prevent high-concentration nanofluid from increasing the viscosity of the base fluid and avoiding excessive flow resistance.

[0041] The nanometer metal or metal oxide particles in the nanomagnetic fluid in the embodiment of the present application have magnetism, and the beneficial effect is that the migration force can be adjusted by applying a magnetic field. In this embodiment, the nanometer particles are preferably ferric oxide.

[0042] The magnetic field is applied by a permanent magnet 7, which is a cylinder with a diameter of 40 mm and a height of 20 mm. The magnetic field of the permanent magnet 7 has two effects. First, before the internal heat transfer of the loop heat pipe 400 is started, the migration activity of the nanoparticles in the magnetic field is high, which can reduce the starting power of the nanofluid working medium 6 from static to dynamic, play a blocking role in the starting stage, enhance the rate of nucleate boiling, bubble generation and growth, and improve the starting performance and heat transfer efficiency. Second, after the nanofluid working medium 6 in the loop heat pipe starts to generate a phase change cycle, under the action of the magnetic field, the nanoparticles are pulled to the evaporation end, so that the nanoparticles create more active nucleation sites.

[0043] As a preferred solution, a float valve 8 is installed inside the hot stick 100, and a permanent magnet 7 is installed on the top of the float valve 8. The permanent magnet 7 and the float valve 8 are arranged at the lower part of the capillary bundle 402 of the evaporator and can change with the liquid level of the liquid ammonia 104 at the bottom of the hot stick 100. The change rule of the magnetic field environment of the loop heat pipe 400 is that the farther the distance between the permanent magnet 7 and the loop heat pipe, the better the circular nature of the magnetic field, the worse the unidirectional nature, and the smaller the magnetic force. The effect of the magnetic field on the nanomagnetic fluid is mainly to reduce the starting resistance and stimulate the phase change activity. When the distance between the permanent magnet 7 and the loop heat pipe is closer, the circular nature of the magnetic field is worse, the unidirectional nature is better, and the magnetic force is larger. The effect of the magnetic field on the nanomagnetic fluid is mainly to reduce the running resistance and improve the circulation efficiency. Therefore, when the air environment temperature is high, the liquid ammonia 104 in the hot stick 100 is mainly accumulated in the upper condensation section 101 in a gaseous state (ammonia gas) and is difficult to liquefy and return, i.e., the hot stick 100 stops running, the liquid level of the liquid ammonia 104 at the bottom of the evaporation section 103 is low, the average distance between the permanent magnet 7 and the loop heat pipe is far, and the magnetic field has a beneficial effect on the loop heat pipe 400, which stimulates the phase change activity and starts the cycle heat transfer. When the air environment temperature is low, the ammonia gas in the condensation section 101 of the hot stick 100 liquefies and returns quickly, i.e., the hot stick 100 is normally running, the liquid level of the liquid ammonia 104 at the bottom of the evaporation section 101 is high, the average distance between the permanent magnet and the loop heat pipe is close, the magnetic field has a beneficial effect on the loop heat pipe 400, which reduces the running resistance and accelerates the cycle heat transfer, and cooperates with the capillary core to drive the liquid nanofluid working medium 6 to move downward, thereby improving the distribution coverage and heat absorption and cooling uniformity of the liquid nanofluid working medium 6 in the evaporation section 103 and improving the permafrost cooling effect.

[0044] Therefore, the beneficial effects of the combination of the loop heat pipe and the nanometer magnetic fluid + permanent magnet are: on the one hand, the high thermal conductivity of nanometer metal or metal oxide particles and the large heat transfer area are used to strengthen heat transfer, especially the active nucleation sites can be increased by the nanometer particles to improve the heat exchange and phase change rate of the working medium; on the other hand, the phase change activity and circulation efficiency of the nanofluid working medium 6 are further improved through the cooperation of the nanofluid and the magnetic field of the permanent magnet. In combination with the difference in the pipe diameter of the evaporator and the condenser 404, the startup limit defect is improved, the requirement for the low temperature value of the atmospheric temperature corresponding to the cold season startup temperature is reduced, and the effective operation time is improved.

[0045] The application adopts the combination of the gravity heat rod unit and the loop heat pipe cluster unit: the gravity heat rod unit is used as the framework, and the loop heat pipe cluster unit is fixed on the gravity heat rod unit, as shown in FIG. 1. Figures 7-11 The specific manufacturing process is as follows: First, the installation position of the liquid reservoir 5 is located at the center position of the bottom end inside the heat rod 100, which is fixed by cross support welding. Secondly, the U-shaped bend I 406 of the loop heat pipe passes through the side wall of the threaded end cap 105 at the top end of the condensing section 101 of the heat rod 100, and the U-shaped bend II 407 of the loop heat pipe 400 passes through the side wall of the threaded end cap 105 at the bottom end of the evaporating section 103 of the heat rod 100, and the passing mode is welding sealing to prevent leakage of the heat transfer working medium 104 in the heat rod 100. Then, the evaporator and the liquid pipeline 405 of each set of loop heat pipe 400 are located inside the heat rod 100, and the condenser 404 and the gas pipeline 403 are located outside the heat rod 100. The gas pipeline 403 is located in the phase change energy storage sleeve 108 outside the evaporating section 103 of the heat rod 100. The condensers 404 of the plurality of loop heat pipes 400 are evenly arranged on the outer wall of the condensing section 101 of the outer heat rod 100, and are fixed on the spiral spoiler 106, and cooperate with the spiral spoiler 106 to form air vortex near the condensing section 101 of the heat rod 100, thereby improving the heat exchange efficiency.

[0046] The heat transfer mode of the combination of the gravity heat rod unit and the loop heat pipe cluster unit is: the technical advantages of the gravity heat rod are large heat transfer capacity and high efficiency, and the technical advantages of the loop heat pipe are low heat resistance and good uniformity. Therefore, on the one hand, the loop heat pipe compensates for the carrying limit and the startup limit defect of the gravity heat rod, so that the startup temperature difference of the enhanced heat rod is significantly lower than that of the conventional gravity heat rod. On the other hand, the high efficient heat transfer performance of the gravity heat rod after starting the phase change cycle in the low temperature atmospheric environment is fully utilized. Therefore, the atmospheric temperature range corresponding to the operation of the enhanced heat rod is widened, and the effective operation time and the cumulative heat exchange of the enhanced heat rod are improved.

[0047] In a specific embodiment of the present application, the radiation refrigeration unit is a dielectric / polymer composite radiation refrigeration film with a 3D porous structure. The film material is used in the following way: it is directly brushed on the outer wall of the condensation section 101 of the heat rod 100, the spiral spoiler 106 and the outer wall of the condenser 404 located outside the condensation section 101.

[0048] The above-mentioned radiation refrigeration film is a zero-energy and zero-pollution cooling technology, whose principle is the internal wide-spectrum selective precise regulation of the material to achieve passive refrigeration. The material improves the spectral performance (solar radiation band reflectivity 98.26%, atmospheric window band emissivity 97.56%) through randomly dispersed aluminum oxide particles and layered disordered micro-nano pores to reduce the solar radiation heat gain of the metal material. The beneficial effects of using the above-mentioned radiation refrigeration film are as follows: On the one hand, the reflectivity to solar radiation is improved, which avoids the rapid warming of the metal pipe material under the action of high-temperature weather and solar radiation, prevents the natural heat energy from being transmitted to the permafrost layer through the metal pipe material when the heat rod stops working in the warm season, and alleviates the negative effects of natural heat erosion in the warm season. On the other hand, the outward emissivity of the metal pipe material is improved, creating a one-way heat transfer path and enhancing the efficiency of capturing natural cold in the cold season. Combined with the special design of the spiral spoiler 106 of the heat rod 100, the condensation limit defect is comprehensively improved, and the heat transfer efficiency is improved.

[0049] In summary, the present application has the following advantages on the basis of fully utilizing the zero-energy consumption, high heat flux density and high capacity heat transfer capability of the gravity heat rod: First, the loop heat pipe cluster is introduced. Firstly, the gas pipeline and the liquid pipeline adopt a separated design, which reduces the flow resistance and utilizes the low thermal resistance heat transfer capability of the loop heat pipe to achieve remote heat transfer cooling of deeper permafrost. Secondly, the evaporator is embedded with a capillary core. Due to the capillary uniform distribution effect, the evaporator cooling and uniform temperature effect is reliable, and the inverse gravity heat transfer capability is utilized, which can operate in microgravity and be used freely between 0°-90°. Second, the radiation refrigeration film and the air spoiler part are introduced, which can capture more natural cold energy under the same air temperature and wind speed conditions, effectively overcome the condensation limit defect, and form a more effective self-cooling heat control system. When applied to permafrost protection, on the one hand, the air temperature range corresponding to effective heat absorption and cooling is widened, overcoming the carrying limit problem of the traditional gravity heat rod when the heat transfer temperature difference is too large, and the starting limit defect when the heat transfer temperature difference is too small, improving the climate environment adaptability. On the other hand, the arrangement angle range of the heat rod is widened, overcoming the deficiency that a single gravity heat rod cannot be arranged horizontally, and improving the permafrost protection scene adaptability.

[0050] The manufacturing process of the enhanced heat rod provided by the present application is as follows: Step 1: Preparation of the pipe body of the heat rod. According to the material and size requirements described above, the pipe body of the gravity heat rod is prepared, as well as the threaded end caps at the top and bottom ends.

[0051] Step 2: Preparation of the components of the loop heat pipe. The evaporator, gas pipeline, condenser and liquid pipeline, liquid reservoir, and U-bend I and U-bend II are prepared respectively.

[0052] Step 3: Welding of the threaded end caps and U-bends. A 20mm diameter hole is drilled at a 60° angle on the side wall of the top threaded end cap, and the U-bend I is inserted into the hole to seal the gap; a 30mm diameter hole is drilled at a 60° angle on the side wall of the bottom threaded end cap, and the U-bend II is inserted into the hole to seal the gap.

[0053] Step 4: Sealing of the gravity heat rod. First, the outlets of the six liquid pipelines are connected to the top inlet of the liquid reservoir, and the inlets of the six evaporator straight pipes are connected to the bottom outlet of the liquid reservoir, and inserted into the pipe body of the heat rod. Second, the inlets of the six liquid pipelines are connected to the outlets of the U-bend I on the top threaded end cap, and the outlets of the six evaporator capillary bundles are connected to the inlets of the U-bend II on the bottom threaded end cap. Then, the top threaded end cap and the bottom threaded end cap are connected and sealed to the pipe body of the gravity heat rod.

[0054] Step 5: Sealing of the loop heat pipe. The outlets of the six condensers are connected to the inlets of the U-bend I on the top threaded end cap, the inlets of the six gas pipelines are connected to the outlets of the U-bend II on the bottom threaded end cap, and the outlets of the six gas pipelines are connected to the inlets of the six condensers one by one. The external condensers are fixed by spiral baffles.

[0055] Step 6: Nanomagnetic fluid working medium filling of the loop heat pipe. First, the nanomagnetic fluid working medium is prepared by a two-step method, i.e., first preparing the nanoparticles, then mixing with the base fluid, and dispersing the nanofluid by adding a dispersant to ensure its stability. At room temperature (25°C), a sol-gel method is used to prepare 10-20nm diameter magnetite particles, which is a mature technology known in the art and will not be described here; second, the prepared magnetite particles are dispersed in liquid ammonia to form a suspension; then the suspension is mixed with anhydrous methanol and a magnetic stirrer and ultrasonic oscillation equipment are used for 30min of dispersion stirring respectively to complete the preparation. Then, a vacuum filling technique is used to inject 350g of nanomagnetic fluid working medium into the loop heat pipe cluster.

[0056] Step 7: Liquid ammonia filling of the gravity heat rod. A vacuum filling technique is used to add a one-way valve to the top threaded end cap, and 2500g of liquid ammonia working medium is injected into the gravity heat rod.

[0057] Step 8, installation of the gravity heat rod outer jacket pipe. The heat preservation jacket pipe and the phase change energy storage jacket pipe are respectively installed and fixed on the outer wall of the heat insulation section and the evaporation section of the gravity heat rod.

[0058] In specific applications, the enhanced heat rod is arranged in the same plane as the ordinary heat rod. As shown in FIGS. Figure 2 、 3 As shown in FIGS. 1-3, the enhanced heat rod is arranged symmetrically on both sides of the roadbed. According to the provisions of the heat rod and heat rod type pipe rack (GB / T 27880), the longitudinal spacing of the ordinary heat rod is generally 3.0-5.0 m, and preferably, the longitudinal spacing of the new heat rod is increased to 5.0-8.0 m. The evaporation section of the enhanced heat rod can be arranged vertically, obliquely or horizontally.

[0059] Compared with the existing heat rod technology, the enhanced heat rod for protecting permafrost has the following beneficial effects: the gravity heat rod is combined with the loop heat pipe technology and the radiation refrigeration technology, the gas pipeline and the liquid pipeline of the loop heat pipe are designed to be separated on the basis of maintaining the zero energy consumption technical feature, a new heat rod device capable of significantly reducing the thermal resistance is formed, the working medium circulation is driven by gravity and capillary force and magnetic force, the technical defects such as the carrying limit, the starting limit and the condensation limit of the conventional gravity heat rod are overcome, the climate adaptability to the atmospheric temperature range in the cold season is widened, the scene adaptability to the permafrost protection of different structures is improved, and the more real-time and effective maintenance of the thermal stability of the permafrost engineering is realized.

[0060] Finally, it should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some technical features. Any modification, equivalent substitution or improvement made within the spirit and principles of the present application shall be included in the scope of protection of the claims of the present application.

Claims

1. An enhanced heat rod for protecting permafrost, characterized by: The application relates to a heat dissipation device for permafrost, which comprises a gravity heat rod unit, a loop heat pipe cluster unit and a radiation refrigeration unit. The loop heat pipe cluster unit comprises a plurality of loop heat pipes which are sequentially connected by an evaporator, a gas pipeline, a condenser and a liquid pipeline. The radiation refrigeration unit is coated on the outer part of the condenser section of the heat rod and the condenser of the loop heat pipe.

2. The reinforced heat rod for protecting permafrost according to claim 1, characterized in that: The heat rod is a sealed hollow pipe which is filled with heat transfer working medium and has a vacuum state in the cavity.

3. The reinforced heat rod for protecting permafrost according to claim 2, characterized in that: The heat transfer working medium in the heat rod is liquid ammonia.

4. The reinforced heat rod for protecting permafrost according to claim 1, wherein: The phase change critical temperature of the phase change energy storage material is between the gasification heat absorption temperature of the heat transfer working medium and the temperature threshold corresponding to the stable state of the permafrost.

5. The reinforced heat probe for protecting permafrost according to claim 4, characterized in that: The outer wall of the condenser section is provided with a spiral spoiler.

6. The reinforced heat rod for protecting permafrost according to claim 1, wherein: The spiral spoiler is an aluminum alloy plate which is spirally wound on the outer part of the condenser section.

7. The reinforced heat rod for protecting permafrost according to claim 1, wherein: The evaporator is divided into two sections, the lower section is a plurality of parallel capillary bundles, and the upper section is a straight-through pipe.

8. The reinforced heat probe for protecting permafrost according to claim 7, characterized in that: The evaporator and the condenser of the plurality of loop heat pipes are connected in parallel.

9. The reinforced heat probe for protecting permafrost according to claim 8, characterized in that: The liquid pipeline of the plurality of loop heat pipes is connected through a liquid storage device. The nanofluid working medium is nanomagnetic fluid.

10. The reinforced heat stick for protecting permafrost according to any one of claims 1-9, characterized in that: The inner part of the nanomagnetic fluid is nanoscale metal or metal oxide particles. The inner part of the heat rod is provided with a float valve. The radiation refrigeration unit is a dielectric / polymer composite radiation refrigeration film with a 3D porous structure.

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