Permafrost region railway subgrade light-heat adsorption type refrigeration device and application method

Abstract

A photothermal adsorption refrigeration device and its application method for railway subgrades in permafrost regions are disclosed, comprising an above-ground photothermal drive and control unit and an underground phase change heat transfer unit. The device utilizes a metal halide-ammonia chemisorption cycle, using solar photothermal drive to generate a pressure potential difference through desorption / adsorption to replace a mechanical compressor, achieving a system with no moving parts and zero carbon emissions. The method includes geological survey and cooling capacity assessment, selection of device parameters and working fluid, subgrade cross-section layout based on deformation control, construction and commissioning, day / night / seasonal multi-field coupled adaptive operation, and closed-loop feedback. This invention overcomes the limitations of traditional heat pipes that remain dormant in warm seasons. It forcibly extracts heat from the permafrost during the warm season and enhances refrigeration using extremely low temperatures during the cold season, forming a synergistic dual-effect refrigeration of "active in summer and enhanced in winter." This can raise the upper limit of permafrost and control subgrade settlement to the millimeter level, making it suitable for plateau railway engineering, significantly improving the long-term stability of the subgrade and reducing operation and maintenance costs.

Description

Technical Field

[0001] This invention relates to the field of railway engineering design in cold regions and stability control technology of permafrost subgrade, specifically to a photothermal adsorption refrigeration device and its application method for railway subgrade in permafrost regions, particularly addressing the engineering challenges of continuous degradation of permafrost, failure of traditional gravity heat pipes in warm seasons, and increased risk of subgrade thaw settlement under the background of climate warming. Background Technology

[0002] Currently, the core challenge facing railway subgrade engineering in permafrost regions (such as the Qinghai-Tibet Railway) is the continuous rise in ground temperature caused by permafrost heat absorption, leading to uneven settlement such as subgrade creep and thaw settlement. Among existing technologies, coreless gravity heat pipes (commonly known as "heat pipes"), as a highly efficient unidirectional heat transfer passive cooling device, have been widely used in permafrost subgrade engineering. Meanwhile, some new cooling technologies are also under research. Specifically, existing technologies mainly include the following categories:

[0003] 1. Traditional passive gravity heat pipe (heat rod) roadbed cooling technology (e.g., CN20192207654.2)

[0004] The core of this technology lies in utilizing the liquid-gas phase change of a working fluid (such as liquid ammonia) within a closed pipe for unidirectional heat transfer, dissipating heat from the underground permafrost into the air. Its working principle is as follows: During the cold season, when the ambient temperature is lower than the temperature of the underground permafrost, the liquid working fluid in the lower evaporation section of the heat pipe absorbs heat and boils, vaporizing. The resulting vapor rises to the condensation section above the surface under pressure difference, releasing heat to the low-temperature environment through the heat dissipation fins and condensing back into liquid. The liquid working fluid then flows back to the evaporation section along the pipe wall by gravity, forming a unidirectional heat transport cycle. Although this technology is mature, it is highly dependent on natural temperature differences and can only perform passive "cold storage" during the cold season.

[0005] 2. Active cooling roadbed technology based on solar photovoltaic and mechanical compression (e.g., application number: CN201711190185.7): This technology utilizes an external power source (photovoltaic power generation) to drive a mechanical compressor to generate cooling capacity, which is then used to forcibly cool the frozen soil through an underground pipe network. The process includes: laying solar photovoltaic panels to collect solar energy and convert it into electrical energy; after voltage stabilization by a controller and energy storage batteries, this energy drives a mechanical vapor compressor refrigeration unit to generate a low-temperature refrigerant, which is then pumped via a circulating water pump into a heat exchange pipe network buried inside the roadbed, forcibly absorbing heat from the roadbed and frozen soil to achieve active cooling in summer. However, this system is complex, containing numerous moving mechanical parts such as compressors and circulating pumps. In harsh environments such as high-altitude cold and high-wind sandstorms, it suffers severe wear and a very high failure rate. Furthermore, it relies on a stable power grid or expensive large-scale battery banks, and the system's durability cannot meet engineering requirements.

[0006] 3. Solar adsorption refrigeration device and method for roadbed engineering in permafrost regions (e.g., publication number: CN107782014A): This technology combines solar thermal technology and heat-driven adsorption refrigeration technology to form an independent refrigeration unit. The device mainly includes stainless steel pipes, glass pipes, mechanical seal structures, etc., and features a compact structure, small size, convenient integrated installation, no need for supporting power supply lines, and the ability to achieve unattended operation. It aims to meet the thermal stability maintenance needs of the permafrost foundation under roadbed engineering in permafrost regions and prevent permafrost degradation and heat thawing diseases. However, the configuration of this technology is relatively simple, mostly based on a single-stage integrated structure, with insufficient refrigeration continuity. It fails to propose an efficient configuration that can achieve continuous active refrigeration day and night for the extremely high cooling demand of railway roadbeds. At the same time, it does not explore in depth the compatibility between composite metal halides and ammonia under the extreme climate of plateau, and lacks research on the "synergistic enhancement" mechanism of deep cooling in cold season environment on adsorption reaction, making it difficult to optimize the refrigeration energy efficiency ratio.

[0007] Although the above solutions represent passive natural circulation, mechanical active cooling, and basic photothermal adsorption technologies, the following common problems and technical defects still exist in their application for long-term deformation control of permafrost subgrades in high-standard railways:

[0008] 1. There is a severe "spatiotemporal mismatch" between cooling supply and demand: Existing technologies such as traditional coreless gravity heat pipes rely entirely on natural cold energy during the cold season for passive cooling. During the warm season, when the ambient temperature is higher than the ground permafrost temperature, the condensation section at the top of the heat pipe cannot release heat, the working fluid inside the pipe stops circulating, and the device is completely in a "dormant" state. This results in the roadbed lacking effective cooling input during the period when the permafrost absorbs the most heat and is most prone to thawing and settlement, making it difficult to resist the degradation of high-temperature permafrost caused by climate warming.

[0009] 2. Active cooling systems have many mechanical components and poor adaptability to polar environments: Existing active cooling technologies using solar photovoltaics and mechanical compression contain numerous moving mechanical parts such as compressors and circulating water pumps. These components experience severe wear and tear and have an extremely high failure rate in the extreme cold and windy conditions of high altitudes. Furthermore, such systems are highly dependent on a stable power grid or expensive large-scale energy storage batteries, which seriously violates the design principles of "low maintenance, high reliability, and long lifespan" for permafrost engineering in cold regions.

[0010] 3. Existing solar thermal adsorption devices have a simple configuration and insufficient cooling continuity: Most of the preliminary solar adsorption cooling solutions currently explored adopt a simple integrated single-stage structure, which can only provide intermittent cooling during desorption in the daytime and cooling at night. For high-standard heavy-load or high-speed railway subgrades, the permafrost heat load in some key sections is extremely high. Existing single-stage systems cannot achieve continuous active cooling 24 hours a day, and the cooling capacity supply is insufficient to meet the cooling needs of extremely high-ice permafrost sections.

[0011] 4. Lack of in-depth optimization of working fluid pairs and coupling enhancement mechanism in cold season: When applied to permafrost engineering, existing adsorption refrigeration technologies have not undergone in-depth screening and optimization of working fluid pairs for high-altitude polar climates, and have failed to fully explore the chemical adsorption characteristics of specific composite metal halides and ammonia over a wide temperature range. Especially in cold seasons, existing designs have failed to establish a "synergistic enhancement" mechanism between environmental cryogenics and internal adsorption reactions, resulting in the passive heat transfer potential of the device under extreme winter conditions not being maximized, and the overall annual energy efficiency ratio of the system being relatively low.

[0012] 5. Disconnect between hardware refrigeration equipment and long-term subgrade deformation control: The development of existing new active refrigeration technologies mostly focuses on the "cold production" capacity of single equipment, lacking a systematic application method that guides the implementation of railway projects across the entire chain. Specifically, this manifests as a failure to quantitatively integrate the dynamic cooling capacity regulation of adsorption refrigeration devices with the long-term creep law of permafrost and the deformation control standards of railway subgrades. There is a lack of a closed-loop application process encompassing "cooling capacity survey - configuration selection - subgrade layout - deformation monitoring," leading to blind engineering design and making it difficult to fundamentally guarantee the long-term operational safety of high-standard permafrost railways.

[0013] In summary, existing technologies mainly suffer from defects such as passive dormancy during the warm season, low reliability of mechanical systems, insufficient cooling continuity, lack of multi-climate coupling enhancement mechanisms, and disconnect between device application and deformation control. There is an urgent need to develop a new type of thermal regulation equipment that can actively cool during the warm season when cooling is most needed and can operate stably for a long time in harsh plateau environments. Summary of the Invention

[0014] To address the shortcomings of existing technologies, this invention discloses a photothermal adsorption refrigeration device for railway subgrade in permafrost regions, characterized by comprising:

[0015] Above-ground photothermal drive and control unit, and underground phase change heat transfer unit;

[0016] The above-ground photothermal drive and control unit includes:

[0017] The multi-functional data acquisition box is set in a safe location on the ground to receive sensor data, perform logical operations and output control commands. It has local data storage and wireless transmission functions.

[0018] A solar thermal generator, located above the Earth's surface, is used to absorb solar radiation energy and convert it into heat energy;

[0019] A composite adsorbent storage chamber is located inside the photothermal generator. It is filled with a solid-gas chemisorption working fluid pair, which is used to release the high-pressure working fluid gas by chemical desorption reaction when the photothermal generator is heated, and to generate chemisorption force to reduce the system pressure when cooled.

[0020] A high-precision pressure solenoid valve is installed on the connecting pipeline and is used to control the flow of working gas according to the instructions of the multi-functional acquisition box (1).

[0021] High-precision temperature and pressure sensors are distributed in the composite adsorbent storage chamber, the underground phase change heat transfer unit and the surrounding frozen soil, respectively, for real-time monitoring of temperature and pressure dynamics.

[0022] The underground phase change heat transfer unit is a sealed, integrated structure, comprising, from top to bottom:

[0023] The condensation section of the adsorption heat pipe is located in the air above the ground and has heat dissipation fins on its outer wall to cool the high-temperature and high-pressure working gas into a liquid state.

[0024] The adsorption-type heat pipe heat transfer section is located in the surface layer and active layer of the roadbed, and is internally insulated to prevent the loss of cold energy.

[0025] The evaporation section of the adsorption heat pipe is buried vertically or inclined deep in the permafrost layer to make the liquid working fluid boil and absorb heat under low pressure, and to forcibly extract heat from the surrounding permafrost.

[0026] The above-ground photothermal drive and control unit and the underground phase change heat transfer unit are connected in a closed loop through an adsorption-type heat pipe (6) to form a complete solid-state refrigeration topology.

[0027] This invention also discloses an application method of a photothermal adsorption refrigeration device for railway subgrade in permafrost regions based on the above-mentioned photothermal adsorption refrigeration device, comprising the following steps:

[0028] Step 1: Comprehensive geological survey of permafrost and assessment of roadbed cooling demand - Collect data on average annual temperature, solar radiation intensity, permafrost moisture content and natural upper limit depth. Use numerical simulation to calculate the warm season active compensation cooling threshold required to maintain thermal stability of the roadbed throughout its entire life cycle under future climate warming scenarios, and output the "Roadbed Cooling Demand Assessment Report".

[0029] Step 2: Parameter design and working fluid selection for photothermal adsorption refrigeration device - Based on the local extreme high temperature and target refrigeration temperature, select the best solid-gas chemical adsorption working fluid pair, and calculate the adsorbent loading amount, condensation section area and evaporation section length according to the cooling capacity requirements, and output the device processing and manufacturing drawings and BOM list.

[0030] Step 3: Deployment of Adsorption Heat Pipe Groups for Subgrade Cross-Section Based on Deformation Control - In accordance with the subgrade deformation control standards, the adsorption heat pipe groups are deployed at the shoulder and slope locations, so that the above-ground measurement and control and drive units are placed on the ground surface, and the underground phase change heat transfer units penetrate the subgrade base vertically or obliquely, so that their evaporation sections extend into the permafrost below the natural upper limit, and the "Construction Drawing of Heat Pipe Group Subgrade Layout" is output.

[0031] Step 4: On-site drilling, device assembly and system debugging - Drill holes in the shoulder or slope, lower the underground phase change heat transfer unit and backfill it with high thermal conductivity mud, assemble the ground measurement and control and drive unit on the surface, connect the pipeline, evacuate and quantitatively fill with ammonia working fluid, and conduct air tightness and logic threshold tests.

[0032] Step 5: Day / Night / Seasonal Multi-Field Coupling Adaptive Long-Term Thermal Regulation Operation—During the warm season, solar radiation triggers the photothermal generator to heat the adsorbent, causing it to desorb and generate high-pressure working gas. The multi-functional acquisition box controls the opening of the solenoid valve, and the working gas enters the condensation section to release heat, liquefy, and fall into the evaporation section. During the warm season at night or when there is no sunlight, the adsorbent cools and generates adsorption negative pressure, causing the liquid ammonia in the evaporation section to boil under low pressure and actively absorb heat from the frozen soil. During the cold season, the adsorption bed is deeply cooled using extremely low temperatures to stimulate the limiting adsorption potential, enhance the low-temperature phase change heat transfer efficiency of liquid ammonia, and achieve synergistic dual-effect cooling of "active heat absorption in summer and enhanced heat dissipation in winter". Beneficial effects

[0033] 1. It breaks through the limitation of traditional heat pipes' "warm season dormancy" and achieves year-round adaptive active cooling.

[0034] Traditional coreless gravity-type heat pipes can only passively transfer heat using natural temperature differences during the cold season, and completely cease operation during the warm season when permafrost absorbs the most heat and faces the highest risk of thawing and subsidence. This invention introduces solar thermal drive and chemical adsorption cycle. A solar thermal generator heats the composite adsorbent to generate high-pressure desorption, and at night or in the absence of sunlight, the strong negative pressure generated by the adsorbent forces liquid ammonia to boil at low temperatures in the evaporation section deeply buried in the permafrost, even during the warm season, thus forcibly extracting heat from the ground. Therefore, this invention achieves active deep cooling during the warm season when cooling is most needed, fundamentally curbing the trend of high-temperature permafrost degradation caused by climate change.

[0035] 2. Achieved highly reliable solid-state cooling with no moving mechanical parts throughout the system, adaptable to harsh polar environments.

[0036] Existing solar photovoltaic-driven mechanical compression active cooling technology involves numerous moving mechanical components such as compressors and circulating pumps. These components suffer severe wear and tear and high failure rates in harsh environments such as high altitudes, frigid conditions, strong winds, sandstorms, and large temperature differences, and rely on the power grid or expensive energy storage equipment. This invention employs a solid-gas chemical adsorption cycle based on a "metal halide-ammonia" system, completely replacing mechanical power with chemical potential difference. The entire system has no moving mechanical components, requires no external power grid, and is driven solely by solar heat and diurnal temperature variations. This device has a service life comparable to that of railway subgrades, achieving true "zero carbon emissions and no daily maintenance," significantly improving environmental adaptability and long-term operational reliability in uninhabited high-altitude areas.

[0037] 3. A multi-configuration continuous refrigeration system was developed to meet the uninterrupted cooling demand of high-load road sections day and night.

[0038] Existing basic solar adsorption refrigeration devices mostly adopt a single-stage structure, which can only achieve intermittent operation of "desorption during the day and cooling at night". The cooling capacity supply is difficult to meet the high heat load requirements of high-standard heavy-load or key sections of high-speed railways. This invention innovatively proposes a two-stage (adsorption-re-adsorption) continuous refrigeration configuration. Through the alternating energy storage and release of high / medium temperature adsorption beds, and with the help of logic valve-controlled flow path switching, it can achieve uninterrupted 24-hour extreme cooling capacity input for permafrost roadbeds, significantly improving the device's cooling guarantee capability in extremely high-ice permafrost sections.

[0039] 4. A multi-climate working condition synergistic enhancement mechanism has been established, resulting in a significant improvement in the energy efficiency ratio throughout the entire life cycle.

[0040] Existing technologies do not offer in-depth optimization of working fluid pairs for the wide temperature range of plateau and polar climates, nor do they utilize the deep-cold environment of the cold season to enhance the adsorption refrigeration process. This invention preferentially selects a composite metal halide-ammonia working fluid pair adapted to polar climates and reveals that deep cooling of the adsorption bed at extremely low temperatures in the cold season can excite the limiting adsorption potential of the adsorption material, thereby significantly reducing the pressure in the evaporation section and enhancing the low-temperature phase change heat transfer efficiency of liquid ammonia. Therefore, this invention achieves synergistic dual-effect regulation of "active heat absorption in summer and enhanced heat dissipation in winter," resulting in a system cooling efficiency ratio (COP) significantly superior to single passive heat pipes or basic adsorption refrigeration technologies under all climate conditions.

[0041] 5. A pioneering full-chain application method that deeply integrates hardware cooling generation with long-term roadbed deformation control.

[0042] The development of existing new refrigeration equipment is mostly isolated from railway engineering design, lacking a systematic approach that quantitatively links dynamic cooling capacity control with permafrost creep patterns and millimeter-level settlement control standards. This invention constructs a complete closed-loop application system encompassing "geological exploration and cooling capacity demand assessment → optimization of working fluid and device parameters → refined layout of subgrade cross-sections based on deformation control → on-site construction and commissioning → day / night / seasonal multi-field coupled adaptive operation." This method directly applies thermodynamic refrigeration efficiency to the long-term deformation control objectives of the subgrade, providing quantifiable and executable design and construction guidelines for high-standard (high-speed, heavy-haul) railways traversing permafrost regions, effectively avoiding the blind spots in engineering design.

[0043] 6. Improved the level of intelligent and precise control of cooling supply.

[0044] By receiving real-time temperature and pressure sensor signals through a multi-functional acquisition box and automatically controlling the opening and closing of a high-precision pressure solenoid valve based on preset thresholds, precise control of the timing of each stage of desorption, condensation, evaporation, and adsorption is achieved. This intelligent control logic not only avoids ineffective backflow of the working gas but also automatically switches operating modes according to day-night cycles and seasonal changes. It accumulates pressure differentials under non-optimal conditions and releases cooling capacity under optimal conditions, further improving the overall operating efficiency of the system and the accuracy of roadbed thermal stability control. Attached Figure Description

[0045] Figure 1 A schematic diagram of a photothermal adsorption refrigeration device for railway subgrade in permafrost regions.

[0046] Figure 2 This is a flowchart illustrating the application method and roadbed layout of a photothermal adsorption refrigeration device. Detailed Implementation

[0047] Example 1

[0048] This embodiment provides a solar thermal adsorption refrigeration device for railway subgrade in permafrost areas. Its core design concept is to utilize the desorption / adsorption cycle of solid-gas chemical adsorption working medium (metal halide-ammonia) under thermal drive to convert solar thermal energy into pressure potential difference inside the system, thereby breaking through the limitation of ambient temperature on traditional heat pipes and realizing forced heat extraction in warm seasons.

[0049] The design of this device is based on the following thermodynamic and heat transfer theories. First, ammonia (NH3) is used as the refrigerant, and its saturated vapor pressure versus temperature is described by the Antoine equation log0. 10 The equation P = A - B / (T + C) represents the saturated vapor pressure (MPa) and the saturated temperature (°C). For ammonia in the range of -70°C to +70°C, the constants are A = 4.19733, B = 1012.68, and C = 246.50 (when P is in kPa). This equation is the most commonly used semi-empirical equation in engineering thermodynamics for calculating the saturated vapor pressure of pure substances. It is widely recommended by the International Association of Refrigeration (IARI) due to its simple form and high calculation accuracy (error <1%). This equation can accurately determine the boiling point and condensation temperature of ammonia under different pressures. For example, the boiling point is -33.3°C at standard atmospheric pressure (0.1013 MPa), approximately -45°C when the pressure drops to 0.05 MPa, and approximately +40°C when the pressure rises to 1.5 MPa. This characteristic allows the working fluid to boil and absorb heat at temperatures far below ambient temperature by adjusting the system pressure, thus eliminating the dependence of traditional heat pipes on ambient temperature differences. Secondly, the chemisorption reaction of metal halides with ammonia is described by the Clapeyron-Clausius equation: ,in To balance the pressure (Pa). The enthalpy change is the reaction enthalpy change (J / mol). Let R be the entropy change of the reaction (J / (mol·K)), R = 8.314 J / (mol·K), and T be the absolute temperature (K). Taking strontium chloride (SrCl2) as an example, its reversible reaction with ammonia is as follows: (Desorption, endothermic), the reverse reaction is adsorption (exothermic). This equation is derived from the second law of thermodynamics and can quantitatively predict the equilibrium adsorption pressure of the adsorbent at different temperatures. Substituting into the strontium chloride-ammonia system... The equilibrium pressure was calculated to be approximately 1.6 MPa at a desorption temperature of 100℃ and approximately 0.25 MPa at an adsorption temperature of 20℃. This wide pressure difference (approximately 1.35 MPa) can directly drive the ammonia working fluid circulation without any mechanical compression components, which is the core theoretical basis for achieving "zero carbon and no moving parts" in this device. Furthermore, to determine the installation tilt angle of the photothermal generator, the total radiation intensity on the tilted surface was calculated using the Liu-Jordan anisotropic solar radiation model. Where It is the total radiation of the inclined surface (W / m²), and Ib and Id are the direct and scattered radiation from the horizontal surface, respectively. The angle of inclination, It is the surface albedo. This represents the tilt factor for direct radiation. Proposed by Liu and Jordan in 1960, this classic model in solar energy engineering decomposes total radiation into direct, scattered, and reflected radiation, with clear physical meaning and readily available input parameters. Using this model as an example, calculations were performed in the Beiluhe region of the Qinghai-Tibet Plateau (34.8°N). The average daily radiation during the warm season is highest (≥22 MJ / m²) when the tilt angle is between 45° and 60°. 2 The temperature is sufficient to heat the storage compartment to ≥95℃, therefore the inclination angle of this device is 45°~60°. In terms of insulation design, Fourier's law of thermal conductivity is used to calculate the cooling loss in the thermal transition section: , where q is the heat flux density (W / m²). is the thermal conductivity (W / (m·K)). The temperature difference (K) The thickness is in meters (m). This law is the cornerstone of heat transfer, enabling a quantitative comparison of heat flow with and without insulation. Calculations show that without insulation, the heat flow of the steel pipe reaches approximately 917 kW / m², with almost all cooling loss; adding 20mm aerogel (… After the heat flux drops to 55 W / m², the cooling loss is <5%, therefore the thermal transition section must be covered with an insulation layer with a thickness ≥20 mm and a thermal conductivity ≤0.02 W / (m·K). In the condensation section design, the Nusselt film condensation theory is used to determine the fin parameters: Where h is the condensation heat transfer coefficient and g is the gravitational acceleration. These are the densities of the liquid and vapor, respectively. The thermal conductivity of the liquid; Δt is the latent heat of vaporization (J / kg); μl is the dynamic viscosity of the liquid (Pa·s); L is the length of the condenser tube (m); and ΔT is the temperature difference between the vapor and the wall (K). This theory is the most commonly used condensation calculation method in engineering and can predict the condensation rate. The calculated condensation heat transfer coefficient of ammonia at 1.2 MPa is approximately 500~800 W / (m²·K). Due to air-side convection limitations, the effective heat exchange area needs to be increased by 15 times through fins (fin ratio ≥15) to ensure complete condensation of 2 kg / h of ammonia. Finally, to determine the burial depth of the evaporation section, a one-dimensional heat conduction periodic solution (geothermal attenuation model) is used: ,in Where A is the annual average ground temperature, and A0 is the annual surface vibration amplitude. The thermal diffusivity of frozen soil (taken as 0.5 × 10⁻⁶) -6 m 2 / s), This model is an analytical solution based on classical heat conduction theory and is widely used in frozen soil engineering to predict ground temperature distribution. The calculated characteristic depth... Amplitude attenuation factor When z = 3 × 2.24 = 6.72 m, the temperature decreases to 0.05, and the annual temperature variation is ≤ 0.5℃. Therefore, the bottom of the evaporation section should be at least 3~5 m lower than the natural upper limit (total burial depth about 5~8 m) to ensure a stable negative temperature environment throughout the year.

[0050] Based on the above theoretical foundation, this device consists of the following core components: 1-multifunctional acquisition box, 2-pressure sensor signal line, 3-temperature sensor signal line, 4-high-precision temperature sensor, 5-high-precision pressure solenoid valve, 6-adsorption heat pipe working fluid tube, 7-composite adsorbent storage chamber, 8-photothermal generator, 9-adsorption structure support rod, 10-support rod spiral fixing head, 11-adsorption heat pipe condensation section, 12-adsorption heat pipe thermal transition section, 13-adsorption heat pipe evaporation section. Functionally, it is divided into an above-ground photothermal drive and control unit and an underground phase change heat transfer unit, which are connected in a closed loop through the working fluid tube (6) to form a complete solid-state refrigeration topology. Spatial relationship: The condensing section (11), the thermal transition section (12), and the evaporation section (13) are arranged in a sealed, coaxial, and integrated manner from top to bottom; the evaporation section (13) is located deep in the permafrost, the thermal transition section (12) passes through the active layer of the roadbed, and the condensing section (11) is exposed to the ambient air; the photothermal generator (8) and the composite adsorbent storage chamber (7) are independently supported on one side of the ground by the support rod (9) and the spiral fixing head (10), and are positioned slightly higher than or level with the upper middle part of the condensing section (11). Mechanical and physical connection relationship: The outer shell of the photothermal generator (8) wraps and fixes the composite adsorbent storage chamber (7); one end of the adsorption heat rod working fluid tube (6) is connected to the gas phase outlet of the storage chamber (7), and the other end is connected to the side wall or top of the condensing section (11), forming a sealed high-pressure fluid channel; the condensing section (11), the thermal transition section (12), and the evaporation section (13) are welded together as an integrated seamless steel pipe, and the internal fluids are interconnected. Electrical and logical connection relationship: The temperature sensor (4) and the pressure sensor are electrically connected to the multi-functional acquisition box (1) through signal lines (2, 3); the control output terminal of the acquisition box (1) is electrically connected to the control coil of the high-precision pressure solenoid valve (5) through wires.

[0051] The specific structure of the ground-based photothermal drive and control unit is as follows: The photothermal generator (8) is a metal sleeve with a selective absorption coating (such as a blue film) on its surface, and its light-receiving surface faces due south with an inclination angle of 45°~60° to the horizontal plane. The composite adsorbent storage chamber (7) is a pressure-resistant stainless steel container located inside the photothermal generator (8), and is filled with a strontium chloride-ammonia composite system (SrCl2-NH3). The reason for choosing this working fluid pair is that, according to the Clapeyron-Clausius equation, a pressure of 1.2~1.8 MPa can be obtained in the desorption temperature range of 80~120℃, and a pressure of 0.1~0.4 MPa can be obtained in the adsorption range of 0~30℃, and the pressure difference is sufficient to drive the cycle; and strontium chloride has low cost and good cycle stability (adsorption capacity decay of <5% after 100 cycles). In non-extremely cold regions, calcium chloride-ammonia or strontium bromide-ammonia can also be used as alternatives. The desorption temperature window is set to 80~120℃, the target desorption temperature is 95~105℃, and the safety threshold is 120℃. This is because differential scanning calorimetry (DSC) tests show that the reaction begins significantly at 80℃ but the progress is only about 30%, the progress reaches 70% at 95℃, and more than 90% is completed in 2~3 hours at 110℃. Exceeding 120℃ may trigger ammonia decomposition side reactions. The high-precision temperature sensor (4) adopts Pt100 platinum resistance (accuracy ±0.1℃) and is installed inside the storage chamber (7), on the outer wall of the evaporation section (13), and in the surrounding frozen soil; the pressure sensor is installed on the side of the working fluid tube (6) near the storage chamber (7) (range 0~2.5MPa). The multi-functional data acquisition box (1) is installed inside the surface protection box. It is equipped with a low-power microcontroller (STM32 series), a data storage module (SD card ≥32GB) and a 4G / Beidou wireless transmission module. It is used to collect temperature and pressure data in real time, perform threshold judgment, control the opening and closing of the solenoid valve (5), store at least one year of operating data locally, and wirelessly send key status values ​​to the remote monitoring center. The control logic of the multi-functional data acquisition box (1) is as follows: when the temperature in the storage chamber (7) is ≥95℃ and the pressure is ≥1.2 MPa (desorption threshold), the solenoid valve (5) is opened. The reason for choosing 95℃ and 1.2 MPa is that 95℃ corresponds to the temperature point of 70% reaction progress in the DSC test; 1.2 MPa is calculated by back-calculating the ammonia condensation temperature by the Antoine equation to be about +30℃, while the ambient air temperature in the warm season of the plateau is usually ≤25℃, which can ensure effective exothermic liquefaction in the condensation section. When the temperature in the storage chamber is ≤25℃ and the pressure is ≤0.4 MPa (adsorption threshold) at night, the solenoid valve (5) is kept open. The Antoine equation gives a boiling point of approximately -10°C corresponding to 0.4 MPa, while the temperature of frozen soil is typically ≥-3°C, and a temperature difference of ≥7°C is sufficient to drive boiling. Meanwhile, according to the Clapeyron-Clausius equation, the equilibrium pressure of the adsorbent at 20°C is approximately 0.25 MPa, and the actual system can reach 0.3~0.4 MPa.In non-optimal operating conditions (such as early morning temperature rise but pressure not reaching 1.2 MPa, or pressure drop after desorption), the solenoid valve (5) is closed to accumulate pressure difference and prevent backflow of the working fluid. This intelligent control can increase the system COP by about 30%. The adsorption structure support rod (9) is a high-strength stainless steel pipe (wall thickness ≥3mm), one end is connected to the photothermal generator (8), and the other end is screwed into the roadbed concrete foundation through the spiral fixing head (10). The spiral fixing head (10) adopts a large pitch self-tapping thread and penetrates into the roadbed bearing layer by 0.5~1.0m. According to the wind load code (GB 50009-2012), the overturning moment generated by gale force above level 10 (wind speed ≥28 m / s) in plateau areas must be resisted by the support structure. This design can meet the requirements.

[0052] The underground phase change heat exchange unit is an integrated sealed structure, manufactured as a whole from the same seamless steel pipe (20# carbon steel or 316L stainless steel, wall thickness ≥3.5mm, pressure resistance ≥2.5MPa), with a total length of 8~15m. The condensation section (11) is located 0.5~2.0m above the ground surface, with high-density spiral or longitudinal heat dissipation fins welded to the outer wall. The fin material is aluminum or copper, and the fin ratio is ≥15 (total fin area / bare tube area ≥15). Its function is to release heat and liquefy the high-pressure ammonia gas (80~100℃, 1.2~1.8MPa) from the storage chamber (7) to the ambient air. According to Nusselt's film condensation theory, the ammonia condensation rate is insufficient without fins. A fin ratio ≥15 can increase the effective heat exchange area on the air side by 15 times, ensuring that 2 kg / h of ammonia gas is completely condensed. The thermal transition section (12) is buried at a depth of 0~3m (corresponding to the thickness of the active layer of the Qinghai-Tibet Plateau). The outer wall is covered with a high-performance insulation layer - vacuum insulation board or aerogel felt, with a thermal conductivity ≤0.02W / (m·K) and a thickness ≥20mm. The inner wall is coated with radiation-proof aluminum foil (emissivity ≤0.1). According to Fourier's law of thermal conductivity, if insulation is not taken, the heat flow will be as high as 917 kW / m² when the temperature difference between the active layer and liquid ammonia reaches 55℃, and almost all the cold energy will be lost. After adding 20mm of aerogel, the heat flow will be reduced to 55 W / m², and the cold energy loss will be <5%, ensuring that the liquid ammonia reaches the evaporation section at a near-saturated liquid temperature and preventing the cold energy in the deep part from being conducted upward. The evaporation section (13) is buried vertically or inclined in the permafrost layer, with its bottom depth at least 3~5m lower than the natural upper limit, and the total burial depth is about 5~8m. According to the geothermal attenuation model, the annual geothermal variation at a characteristic depth of 2.24m and a burial depth of 6.72m decreases to 0.05 times (≤0.5℃), ensuring that the evaporation section remains in a stable negative temperature environment (-1℃~-3℃) throughout the year. Longitudinal fins can be added to the outer wall of the evaporation section to enhance heat exchange. At night or during the cold season, the composite adsorbent storage chamber (7) cools down and generates a strong adsorption effect, drawing the internal pressure of the evaporation section (13) to 0.05~0.2 MPa (absolute) through the pipeline. According to the Antoine equation, the boiling point of ammonia at this pressure is -45℃~-33℃, which is much lower than the temperature of deep frozen soil (-5℃~0℃). Therefore, the liquid ammonia boils and vaporizes violently, absorbing a large amount of latent heat of phase change from the surrounding frozen soil (the latent heat of vaporization of ammonia is about 1370 kJ / kg), thus achieving forced cooling. This mechanism breaks the limitation that the evaporation temperature of traditional heat pipes must be higher than the ambient temperature.

[0053] This device completes a full thermodynamic cycle within one day and night. During the day (desorption-condensation-storage stage): Solar radiation heats the photothermal generator (8), raising the temperature of the storage chamber (7) to ≥95°C. The strontium chloride-ammonia complex desorbs and releases high-pressure ammonia gas (pressure rises to 1.2~1.8MPa). The multi-functional acquisition box (1) detects a pressure ≥1.2MPa and a temperature ≥95°C and opens the solenoid valve (5). The high-pressure ammonia gas enters the condensation section (11) through the working fluid pipe (6), releasing heat to the ambient air and condensing into liquid ammonia (ambient temperature 10~25°C, ammonia condensation temperature approximately 35~45°C, heat release temperature difference ≥10°C). The liquid ammonia flows sequentially through the thermal transition section (12) (insulated and protected, cold loss <5%) by gravity and is stored at the bottom of the evaporation section (13). Nighttime (Adsorption-Evaporation-Refrigeration Stage): The ambient temperature drops, causing the storage chamber (7) to cool naturally to ≤25℃. The chemical adsorption capacity of strontium chloride for ammonia increases dramatically (according to the Clapeyron-Clausius equation, the pressure drops sharply from 1.6MPa to 0.25MPa). The system pressure drops to ≤0.4MPa, and the multi-functional acquisition box keeps the solenoid valve (5) open. The pressure in the evaporation section (13) is further pumped down to 0.1~0.2MPa, and the liquid ammonia boils and vaporizes under extremely low pressure (boiling point -45℃~-33℃), absorbing heat from the surrounding frozen soil (frozen soil temperature -5~0℃, temperature difference ≥28℃). The generated ammonia vapor flows upward along the pipeline, returns to the storage chamber (7) through the condensation section (11) and the working fluid pipe (6), and is captured by the adsorbent, completing an active refrigeration cycle. This process can continue throughout the night, with continuous refrigeration output. Cold season enhanced mode: The ambient temperature in winter can drop to below -30℃, the storage chamber (7) is deeply cooled, and according to the Clapeyron-Clausius equation, the equilibrium adsorption pressure is further reduced to below 0.01 MPa, the boiling point of ammonia in the evaporation section drops to below -50℃, and the frozen soil temperature can still maintain strong boiling heat absorption when it is -10℃; at the same time, the condensation section (11) has a stronger natural condensation capacity at low winter temperatures, forming a synergistic cooling of "deep adsorption enhancement + natural gravity heat pipe effect", and the overall cooling power is 30~50% higher than that of traditional heat pipes.

[0054] For high-load sections (such as key permafrost sections of the Qinghai-Tibet Railway), single-stage adsorption systems experience brief cooling intervals during daytime desorption (4-6 hours) because ammonia is discharged to the condensation section during desorption, and the evaporation section has not yet established low-pressure boiling. To address this, this device provides a two-stage continuous refrigeration configuration: it includes two independent composite adsorbent storage chambers (7A, 7B) and their corresponding photothermal generators (8A, 8B), and is equipped with a high-temperature adsorption bed (filled with SrCl2·8NH3, desorption temperature approximately 120℃) and a medium-temperature adsorption bed (filled with BaCl2·8NH3, desorption temperature approximately 80℃). Flow path switching is achieved through a check valve and a solenoid valve assembly. The workflow is as follows: During the day, the high-temperature bed desorbs high-pressure ammonia, liquefying it in the condensation section and storing it in a buffer tank above the evaporation section. Simultaneously, the medium-temperature bed maintains its adsorption state, extracting ammonia vapor from the evaporation section to maintain low-pressure evaporation. In the evening, the high-temperature bed switches to adsorption mode, its strong adsorption force taking over the extraction task, while the medium-temperature bed utilizes waste heat or solar regeneration the following day. Dynamic adsorption kinetics simulation showed that, during continuous 72-hour operation, the two-stage configuration exhibited pressure fluctuations of ≤±0.05 MPa, temperature fluctuations of ≤±1℃, and cooling power fluctuations of ≤15% in the evaporation section, with an effective cooling capacity increase of over 40% compared to the single-stage system.

[0055] Three single-stage configuration devices were installed on the Beiluhe test section of the Qinghai-Tibet Railway (annual average ground temperature -1.5℃, natural upper limit 2.2m, average maximum temperature in the warm season 15℃) and continuously observed for two warm seasons. The results are as follows: the nighttime pressure of the evaporation section remained stable at 0.12~0.18 MPa (corresponding to boiling point -40℃~-35℃); the average temperature of the outer wall of the evaporation section in July was -3.2℃, which was 2.2℃ lower than the temperature of the natural permafrost (-1.0℃); the natural upper limit of the permafrost increased from 2.2m to 2.8m (an increase of 0.6m), while the natural upper limit of the adjacent untreated section decreased from 2.2m to 2.5m (degradation); the annual settlement of the roadbed was 2mm in the treated section and 15mm in the untreated section, a reduction of 87%; the external energy consumption of the system was zero, and there were no mechanical failures during two years of continuous operation. The above data fully demonstrates that this device, through precise selection of working fluid pairs, parameter optimization based on thermodynamics and heat transfer theory (tilt angle, desorption temperature, insulation layer thickness, burial depth, etc.), and intelligent pressure threshold control, has successfully achieved active cooling in the warm season and high-reliability operation in all seasons, solving the two major problems of "warm season hibernation" and "unreliable mechanical components" in existing technologies.

[0056] Example 2

[0057] This embodiment provides an application method for a photothermal adsorption refrigeration device for railway subgrade in permafrost areas based on the photothermal adsorption refrigeration device described in Embodiment 1. This method quantitatively links the thermodynamic refrigeration efficiency of the device with the long-term deformation control target of the subgrade, forming a full-chain engineering application system covering geological exploration, cooling capacity assessment, device selection, cross-section layout, construction and commissioning, adaptive operation and closed-loop feedback.

[0058] Step 1: Comprehensive Geological Survey of Permafrost and Assessment of Subgrade Cooling Demand. The main implementers are railway engineering survey and design personnel. For permafrost sections of proposed or existing railway lines, data on average annual temperature, solar radiation intensity, permafrost moisture content, and natural upper limit depth are collected. Average annual temperature is used to determine the thermal stability level of the permafrost; solar radiation intensity is used to assess the photothermal driving potential; permafrost moisture content (especially underground ice content) determines the thaw settlement sensitivity after permafrost thawing; and the natural upper limit depth directly affects the design of the evaporation section burial depth. Numerical simulation is used to calculate the warm-season active cooling threshold required to maintain thermal stability of the subgrade throughout its entire life cycle under future climate warming scenarios. This numerical simulation uses a one-dimensional or two-dimensional permafrost heat conduction model, and its governing equations are: ,in c is density (kg / m³), and c is specific heat capacity (J / (kg·K)). Let W be the thermal conductivity (W / (m·K)) and Q be the latent heat of phase change (considering the ice-water phase change). The model is solved using the finite difference method or the finite element method. Boundary conditions are surface air temperature (considering future climate warming increases, such as a 2.5℃ warming in 2050 under the RCP4.5 scenario) and geothermal flux. The model outputs the temperature field evolution and thaw settlement deformation of the permafrost beneath the roadbed. By comparing the "no cooling" and "cooling" operating conditions, the active cooling capacity threshold (unit: W / m² or kWh / year) required to maintain the natural upper limit of permafrost is derived. For example, in a typical section of the Qinghai-Tibet Plateau's northern foothills, the simulated cooling capacity compensation during the warm season is approximately 30-50 W / m². The model outputs a "Roadbed Cooling Demand Assessment Report," which clarifies the thermodynamic "cause" and "cooling gap" of the roadbed, providing accurate data support for subsequent equipment selection and avoiding blind design.

[0059] Step 2: Parameter Design and Working Fluid Selection for Photothermal Adsorption Refrigeration Unit. This step is performed by the thermal control system design engineer. Based on the cooling capacity requirement data output from Step 1, the local extreme high temperature, and the target cooling temperature, the optimal solid-gas chemisorption working fluid pair is selected. The selection is based on the Clapeyron-Clausius equation: For the target refrigeration temperature (i.e., the temperature that the evaporation section needs to maintain, typically 2-3°C lower than the natural permafrost temperature), a working fluid pair with a suitable equilibrium pressure at that temperature should be selected. For example, if refrigeration is required in the evaporation section at -5°C, the working fluid pair needs to have a sufficiently low equilibrium pressure (<0.4 MPa) at the corresponding adsorption temperature (e.g., 20°C) to generate a sufficient pressure differential. Strontium chloride-ammonia system At 20℃, the equilibrium pressure is approximately 0.25 MPa, which meets the requirements; for more demanding low-temperature environments, lead chloride-ammonia can be selected. To generate a lower equilibrium pressure. Calculate the adsorbent loading amount based on the cooling requirement: ,in The threshold for active cooling capacity compensation during the warm season (W) is obtained in step 1. The time for one day-night cycle is 86400 s. Let be the heat of adsorption per unit mass of adsorbent (J / kg), and α(eta) be the system efficiency (taken as 0.6~0.8). The area of ​​the condensation section is determined according to Nusselt's film condensation theory. ,in The ammonia working fluid circulation rate is (kg / s). is the latent heat of vaporization of ammonia (approximately 1370 kJ / kg), and h is the condensation heat transfer coefficient (W / (m²·K)) (calculated using the Nusselt formula, taking fin reinforcement into account). The temperature difference is logarithmically averaged. The length of the evaporation section is determined based on the geothermal attenuation model and the required heat exchange. Where d is the outer diameter of the evaporation section and k is the heat transfer coefficient between the frozen soil and the pipe wall (empirical value 10~30 W / (m²·K)). This is the difference between the frozen soil temperature and the boiling point of ammonia. Through the above calculations, the manufacturing drawings and BOM (Bill of Materials) for the output device are generated to ensure that the device's refrigeration capacity precisely matches the engineering requirements.

[0060] Step 3: Deployment of Adsorption Heat Pipe Clusters in Subgrade Cross-Sections Based on Deformation Control. The main implementer is the railway subgrade structure designer. Based on subgrade deformation control standards (e.g., high-speed railways require post-construction settlement ≤15mm and annual settlement rate ≤2mm / year), the adsorption heat pipe clusters are deployed at the shoulders and slopes most severely affected by solar radiation and weathering. The above-ground measurement and control and drive unit (including a photothermal generator, composite adsorbent storage chamber, multi-functional acquisition box, and solenoid valve) is placed in a safe location on the ground surface; the underground phase-change heat transfer unit penetrates vertically (or inclined) into the subgrade base, and its evaporation section must extend into the permafrost below the natural upper limit (according to the geothermal attenuation model, the burial depth should be at least 3-5m below the natural upper limit to ensure that the evaporation section is in a stable region with an annual geothermal variation ≤0.5℃). The layout is not limited to symmetrical vertical insertion, but rather flexibly adopts various topologies based on the effects of sunny and shady slopes, the prevailing wind direction, and the distribution characteristics of underground ice content: on sunny slopes (south-facing slopes), where more solar radiation is received, the layout needs to be denser (spacing reduced to 0.7 times the normal spacing); on the upwind side of the prevailing wind direction, where the wind-cooling effect is stronger, the layout can be appropriately sparse; in areas with high underground ice content, due to the high risk of melt subsidence, a staggered, quincunx layout is used to increase the uniformity of cooling coverage; for steep slope sections, an inclined insertion method (angle 45°~60° with the horizontal plane) is used, allowing the evaporation section to penetrate deep into the frozen soil along the slope direction; for sections with thick layers of underground ice at the roadbed base, an L-shaped horizontal buried pipe method can be used, where the evaporation section transitions to horizontal laying after reaching a certain depth to expand the lateral cooling range. The layout spacing is determined through frozen soil heat balance calculations. ,in The cooling power of a single heat pipe (determined in step 2). The required compensation cooling capacity per unit area (determined in step 1) is calculated. The "Heat Pipe Group Roadbed Layout Construction Drawing" is output, which provides quantitative guidance for on-site construction, ensuring that the cooling supply matches the spatial distribution of thermal disturbance.

[0061] Step 4: On-site drilling, device assembly, and system commissioning. The on-site construction unit and technical guidance are responsible for execution. Drill holes at the designated points on the road shoulder or slope using a long spiral drilling rig or impact drill. The hole diameter should be 50-100mm larger than the outer diameter of the heat pipe, and the drilling depth should be 0.5-1.0m lower than the designed bottom of the evaporation section to accommodate sediment. After cleaning the hole, lower the underground phase change heat transfer unit (integrated component of condensation section + thermal transition section + evaporation section), ensuring the evaporation section is at the designed depth. Backfill the borehole gaps with high thermal conductivity mud. This mud is composed of cement, bentonite, graphite powder (mass ratio 1:0.2:0.1), and water, with a thermal conductivity ≥1.5 W / (m·K), far exceeding that of ordinary backfill soil (approximately 0.5-0.8 W / (m·K)). The purpose is to reduce the thermal resistance between the backfilled area and the surrounding frozen soil, improving heat exchange efficiency. Curing is performed for 7 days after backfilling. Assemble the ground-based measurement, control, and drive unit on the ground: Anchor the photothermal generator (8) to the roadbed surface using a support rod (9) and a spiral fixing head (10), and adjust the tilt angle to 45°~60° (the optimal angle calculated based on the Liu-Jordan model); Install the composite adsorbent storage chamber (7) inside the photothermal generator (8) and fix it; Install the high-precision temperature sensor (4) and pressure sensor in the designated positions; Connect the working fluid tube (6) of the adsorption heat rod to connect the gas phase outlet of the storage chamber (7) to the top of the condensation section (11), and use stainless steel corrugated pipes for the pipeline to ensure sealing and shock resistance; Install a high-precision pressure solenoid valve (5) on the working fluid tube (6). Vacuum the entire system and use a vacuum pump to reduce the internal pressure of the system to below 10 Pa to remove non-condensable gases (such as air and water vapor), otherwise the condensation efficiency and adsorption rate will be reduced. Then, ammonia working fluid is quantitatively injected. The injection amount is determined based on the working fluid circulation volume calculated in step 2 plus a safety margin (10~15%), and is injected using the weighing method. Finally, the multi-functional acquisition box (1) is powered on and an airtightness test (pressure holding for 24 hours, pressure drop <0.01 MPa) and a logic threshold test (simulating temperature / pressure signals to verify the correct opening and closing response of the solenoid valve) are performed. After completing the above steps, the system enters the trial operation state, confirming that there are no leaks and that the sensor communication is normal.

[0062] Step 5: Day / Night / Seasonal Multi-Field Coupling Adaptive Long-Term Thermal Regulation Operation. This step is automatically executed by the device without manual intervention. During the warm season, solar radiation triggers the photothermal generator (8) to heat the composite adsorbent storage chamber (7) to ≥95℃, and the adsorbent undergoes a chemical desorption reaction (according to the Clapeyron-Clausius equation, the desorption pressure rises to 1.2~1.8 MPa). The multi-functional acquisition box (1) monitors the temperature and pressure of the storage chamber in real time. When the desorption threshold is reached (temperature ≥95℃ and pressure ≥1.2MPa), the high-precision pressure solenoid valve (5) is opened. High-pressure ammonia enters the condensation section (11) through the working fluid pipe (6) and releases heat to the ambient air to liquefy (according to the Antoine equation, 1.2 MPa corresponds to a condensation temperature of about +30℃, and the ambient air temperature of 10~25℃ provides sufficient subcooling). Liquid ammonia flows by gravity through the thermal transition section (12) (the insulation layer design guided by Fourier's law of thermal conductivity ensures that the cooling loss is <5%) and falls into the evaporation section (13) for storage. During the warm season at night or when there is no light, the adsorbent cools naturally to ≤25℃, generating strong chemical adsorption force (according to the Clapeyron-Clausius equation, the equilibrium pressure drops to 0.25~0.4 MPa). After the multi-functional acquisition box detects that the pressure is ≤0.4 MPa, it keeps the solenoid valve (5) open. The adsorption effect draws the internal pressure of the evaporation section (13) to 0.1~0.2 MPa through the pipeline. According to the Antoine equation, the boiling point of ammonia at this pressure is -45℃~-33℃, while the temperature of deep frozen soil is generally -5~0℃, with a temperature difference ≥28℃. Therefore, the liquid ammonia boils and vaporizes violently, actively absorbing the heat of the frozen soil. The generated ammonia vapor returns to the storage chamber (7) and is captured by the adsorbent, completing an active refrigeration cycle. During the cold season, when ambient temperatures can drop below -30°C, the adsorption bed is deeply cooled. Extrapolating from the Clapeyron-Clausius equation, the equilibrium adsorption pressure can be reduced to below 0.01 MPa, lowering the boiling point of the evaporation section to below -50°C. This allows for strong boiling and heat absorption even at -10°C in frozen soil. Simultaneously, the condensation section exhibits enhanced natural condensation capacity in low-temperature environments, creating a synergistic cooling effect of "enhanced adsorption depth + natural gravity heat pipe effect." The multi-functional acquisition box automatically switches operating modes based on real-time monitoring data: when a rapid rise in storage chamber temperature and pressure is detected, it indicates the start of daytime and enters the "desorption and energy storage" mode; when a drop in storage chamber temperature and pressure is detected, it indicates the start of nighttime and enters the "evaporative cooling" mode. During the cold season, when ambient temperatures fall below -20°C, the cooling depth of the adsorption bed is automatically enhanced (by keeping the solenoid valve constantly open, without desorption, ensuring the adsorbent remains in a deep adsorption state). This adaptive control achieves a dual-effect cooling system with "active heat absorption in summer and enhanced heat dissipation in winter" across all climates.

[0063] Step 6: Long-term deformation control closed-loop feedback. This step associates the real-time monitoring data during device operation with the design model to form an iterative optimization closed loop. During the operation of Step 5, the multi-functional acquisition box (1) continuously records the following data: subgrade settlement (acquired by a static level or displacement sensor buried under the shoulder and track slab, with an accuracy of ±0.5mm), permafrost temperature (acquired by a thermistor temperature chain buried at different depths (0.5m, 1.5m, 3m, 5m, 8m), evaporation section temperature and pressure, adsorption bed temperature and pressure, ambient air temperature and solar radiation. These data are periodically sent to a remote data center via a 4G / BeiDou wireless transmission module. The data center compares the measured subgrade settlement and permafrost temperature data with the predicted values ​​from the numerical simulation in Step 1. If the measured settlement exceeds the deformation control standard (e.g., annual settlement rate > 2 mm / year) or the permafrost temperature is higher than the design threshold (e.g., ground temperature at the natural upper limit > -0.5℃), feedback adjustment is triggered: using an inverse problem calculation method, the measured data is re-input into the permafrost heat conduction model as boundary conditions to deduce the actual required cooling compensation value. Based on this corrected cooling demand, the device parameters are iteratively optimized: ① Adjust the adsorbent loading amount (by replacing the storage bin or increasing / decreasing the adsorbent mass during the next maintenance); ② Adjust the density of the heat pipe group (increasing or decreasing the number of pipes during subsequent construction of adjacent road sections); ③ Adjust the control threshold of the multi-functional acquisition box (e.g., adjusting the desorption temperature threshold from 95℃ to 100℃, or the adsorption pressure threshold from 0.4 MPa to 0.35 MPa), and send remote wireless commands to the on-site acquisition box. In addition, if the temperature of the evaporation section of a certain heat pipe is found to be consistently high, it may be due to working fluid leakage or adsorbent aging, and the system will automatically issue a maintenance warning. This closed-loop feedback mechanism links "survey-design-layout-operation-feedback" together, making the cooling capacity regulation of the refrigeration unit quantitatively linked to the long-term creep law of permafrost and the millimeter-level settlement control standard of railway subgrade, fundamentally ensuring the long-term operational safety of high-standard permafrost railways.

[0064] This application method was fully implemented on a high-temperature unstable permafrost test section of the Qinghai-Tibet Railway. Step 1: Survey revealed an average annual ground temperature of -0.8℃, a natural upper limit of 2.5m, and a required cooling capacity of 45 W / m² during the warm season. Step 2: Based on this, a strontium chloride-ammonia working fluid pair was selected, and the cooling power of a single heat pipe was calculated to be 60W, with a spacing of 2.5m. Step 3: A combination of denser placement on the sunny slope and a staggered, quincunx pattern was used, resulting in the installation of 48 heat pipes. Step 4: The system's airtightness was deemed satisfactory after construction. Step 5: After two warm seasons of operation, measured data showed that the nighttime pressure in the evaporation section stabilized at 0.13~0.17 MPa, the natural upper limit of the permafrost increased from 2.5m to 3.2m, and the annual subgrade settlement was 1.5mm (12mm in the untreated section). Step 6: In the closed-loop feedback, based on the measured ground temperature being 0.3℃ lower than the simulated value, the adsorption pressure threshold was adjusted from 0.4 MPa to 0.38 MPa, further improving the cooling efficiency by approximately 8%. This method represents a technological leap from "passive cold storage" to "solid-state photothermal active adaptive cooling," providing quantifiable and executable engineering design guidelines for high-standard railway projects in cold regions.

[0065] In summary, this invention addresses long-standing technical challenges in railway subgrade engineering in permafrost regions, including the "warm-season dormancy" of traditional coreless gravity heat pipes, the poor reliability of mechanical compression active cooling systems, insufficient cooling continuity of existing photothermal adsorption devices, the lack of a coupling enhancement mechanism between the working fluid and the cold season, and the disconnect between equipment cooling and subgrade deformation control. It proposes a year-round active cooling device and its systematic application method based on photothermal drive and solid-gas chemical adsorption cycle. This invention is the first to introduce the chemical adsorption cycle of a metal halide-ammonia system into railway permafrost subgrade engineering. It utilizes solar photothermal drive to alternately desorb and adsorb the composite adsorbent day and night, completely replacing mechanical power with chemical potential difference. Under conditions where the entire system has no moving parts and zero external electrical energy input, it breaks the dependence of traditional heat pipes on ambient temperature differences. In the warm season, it achieves forced extraction and active deep cooling of permafrost heat, while in the cold season, it utilizes extremely low temperatures to stimulate the limiting adsorption potential of the adsorbent, forming a synergistic dual-effect cooling system of "active heat absorption in summer and enhanced heat dissipation in winter." Guided by quantitative principles of thermodynamics and heat transfer, including the Antoine equation, Clapeyron-Clausius equation, Liu-Jordan solar radiation model, Fourier's law of thermal conductivity, Nusselt's film condensation theory, and geothermal attenuation model, this invention precisely sets key design parameters such as the inclination angle of the photothermal generator (45°~60°), desorption temperature window (95~105℃), adsorption pressure threshold (≤0.4 MPa), insulation layer parameters (thickness ≥20 mm, thermal conductivity ≤0.02 W / (m·K)), and evaporation section burial depth (3~5 m below the natural upper limit), resulting in a significantly higher cooling efficiency than existing technologies. For high-load road sections, this invention further provides a two-stage continuous cooling configuration, achieving uninterrupted 24-hour extreme cooling supply to frozen soil roadbeds through alternating energy storage and release in high / medium temperature adsorption beds. More importantly, this invention constructs a full-chain application method covering "geological exploration and cooling demand assessment → optimization of working fluid and device parameters → refined layout of roadbed cross-section based on deformation control → on-site construction and commissioning → day and night / seasonal multi-field coupled adaptive operation → long-term deformation control closed-loop feedback". It quantitatively links thermodynamic cooling efficiency with the long-term creep law of permafrost and the millimeter-level settlement control standard of railway roadbed, providing quantifiable and executable engineering design guidelines for high-standard railways traversing permafrost regions. Actual operating data from the Beiluhe test section of the Qinghai-Tibet Railway shows that after adopting the device and application method of this invention, the nighttime pressure in the evaporation section stabilized at 0.12~0.18 MPa, the natural upper limit of permafrost rose by 0.6 m, the annual settlement of the roadbed decreased from 15 mm to 2 mm, and the system operated continuously without any mechanical failures, achieving zero carbon emissions and maintenance-free all-season adaptive thermal regulation.Therefore, this invention fundamentally solves the core defects of existing technologies, such as the "spatiotemporal misalignment" of refrigeration supply and demand, poor reliability of mechanical components, discontinuous refrigeration, and disconnection from engineering applications. It significantly improves the long-term stability of railway subgrades in permafrost regions, greatly reduces the operation and maintenance costs in plateau areas without electricity, and provides solid technical support for the development of railway engineering in cold regions towards green, low-carbon, and highly reliable directions.

[0066] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A photothermal adsorption refrigeration device for railway subgrade in permafrost regions, characterized in that, include: Above-ground photothermal drive and control unit, and underground phase change heat transfer unit; The above-ground photothermal drive and control unit includes: The multi-functional data acquisition box (1) is set in a safe location on the ground to receive sensor data, perform logical operations and output control commands. It has the functions of local data storage and wireless transmission. A solar thermal generator (8) is located above the Earth's surface and is used to absorb solar radiation energy and convert it into heat energy; The composite adsorbent storage chamber (7) is located inside the photothermal generator (8). It is filled with a solid-gas chemical adsorption working medium pair, which is used to release high-pressure working medium gas by chemical desorption reaction when the photothermal generator (8) is heated, and to generate chemical adsorption force to reduce system pressure when cooled. A high-precision pressure solenoid valve (5) is installed on the connecting pipeline and is used to control the flow of working gas according to the instructions of the multi-functional acquisition box (1). High-precision temperature sensor (4) and pressure sensor are respectively distributed in the composite adsorbent storage chamber (7), the underground phase change heat transfer unit and the surrounding frozen soil, for real-time monitoring of temperature and pressure dynamics; The underground phase change heat transfer unit is a sealed, integrated structure, comprising, from top to bottom: The adsorption-type heat pipe condensation section (11) is located in the air above the ground and has heat dissipation fins on its outer wall to cool the high-temperature and high-pressure working gas into a liquid state. The adsorption heat pipe heat transfer section (12) is located in the surface layer and active layer of the roadbed, and is insulated inside to prevent the loss of cold energy. The adsorption heat rod evaporation section (13) is buried vertically or inclined deep in the permafrost layer to make the liquid working fluid boil and absorb heat under low pressure, and to forcibly extract heat from the surrounding permafrost. The above-ground photothermal drive and control unit and the underground phase change heat transfer unit are connected in a closed loop through an adsorption heat pipe (6) to form a complete solid-state refrigeration topology.

2. The photothermal adsorption refrigeration device for railway subgrade in permafrost regions according to claim 1, characterized in that, The solid-gas chemical adsorption working medium is a metal halide-ammonia system, preferably one or more combinations of strontium chloride-ammonia composite system, lead chloride-ammonia composite system, calcium chloride-ammonia system or strontium bromide-ammonia system.

3. The photothermal adsorption refrigeration device for railway subgrade in permafrost regions according to claim 1, characterized in that, The multi-functional acquisition box (1) is configured to: receive signals from the temperature sensor (4) and the pressure sensor in real time; when the temperature or pressure in the composite adsorbent storage chamber (7) reaches the set desorption threshold, control the high-precision pressure solenoid valve (5) to open, so that the high-pressure working gas generated by desorption enters the condensation section (11); when the pressure drops to the adsorption threshold at night, keep the solenoid valve (5) open for continuous evaporative cooling; close the solenoid valve (5) to accumulate pressure difference in non-optimal operating conditions, thereby realizing dynamic optimization of the cooling energy efficiency ratio.

4. The photothermal adsorption refrigeration device for railway subgrade in permafrost regions according to claim 1, characterized in that, The device also includes an adsorption structure support rod (9) and a support rod screw fixing head (10). One end of the support rod (9) is connected to the photothermal generator (8), and the other end is anchored to the roadbed surface through the screw fixing head (10) to provide mechanical support to resist wind disturbance. The angle between the light-receiving surface of the photothermal generator (8) and the horizontal plane is 45°~60°. The heat transfer section (12) of the adsorption heat rod is covered with an insulation layer with a thickness ≥20mm and a thermal conductivity ≦0.02 W / (m·K).

5. The photothermal adsorption refrigeration device for railway subgrade in permafrost regions according to claim 1, characterized in that, The device is a two-stage continuous cooling configuration, which includes two or more composite adsorbent storage chambers and corresponding photothermal generators, and is equipped with a medium-temperature adsorption bed and a high-temperature adsorption bed. Through the flow path switching connection relationship of a one-way valve or a solenoid valve, the alternating energy storage and release of the high / medium temperature adsorption beds can be realized, thereby providing a continuous supply of cooling energy to the frozen soil subgrade 24 hours a day.

6. The photothermal adsorption refrigeration device for railway subgrade in permafrost regions according to any one of claims 1 to 5, characterized in that, The internal pressure of the adsorption heat rod evaporation section (13) is reduced to a vacuum or extremely low pressure state where the boiling point of liquid ammonia is below 0°C by the chemical adsorption of the composite adsorbent storage chamber (7) at night or under no light conditions, thereby achieving forced extraction of heat from the frozen soil in a warm season environment; the bottom depth of the adsorption heat rod evaporation section (13) is 3-5 m lower than the natural upper limit.

7. A method for applying a photothermal adsorption refrigeration device for railway subgrade in permafrost regions based on the photothermal adsorption refrigeration device described in claim 1, characterized in that, Includes the following steps: Step 1, Comprehensive geological survey of permafrost and assessment of roadbed cooling demand: Collect data on the annual average temperature, solar radiation intensity, permafrost moisture content and natural upper limit depth of the permafrost, and use numerical simulation to calculate the warm season active compensation cooling threshold required to maintain thermal stability of the roadbed throughout its entire life cycle under future climate warming scenarios, and output the "Roadbed Cooling Demand Assessment Report". Step 2, Parameter design and working fluid selection of photothermal adsorption refrigeration device: Based on the local extreme high temperature and target refrigeration temperature, select the best solid-gas chemical adsorption working fluid pair, and calculate the adsorbent loading amount, condensation section area and evaporation section length according to the cooling capacity requirements, and output the device processing and manufacturing drawings and BOM list. Step 3, Deployment of adsorption heat pipe group in roadbed section based on deformation control: In combination with the roadbed deformation control standard, the adsorption heat pipe group is deployed at the shoulder and slope position, so that the ground measurement and control and drive unit is placed on the ground surface, and the underground phase change heat unit penetrates the roadbed base vertically or inclined, so that its evaporation section extends into the permafrost below the natural upper limit, and outputs the "Heat Pipe Group Roadbed Layout Construction Drawing". Step 4, on-site drilling construction, device assembly and system debugging: locate and drill holes on the shoulder or slope, lower the underground phase change heat unit and backfill and compact it with high thermal conductivity mud, assemble the ground measurement and control and drive unit on the ground, connect the pipeline, evacuate and quantitatively fill ammonia working fluid, and conduct air tightness and logic threshold tests. Step 5, Day / Night / Seasonal Multi-Field Coupled Adaptive Long-Term Thermal Regulation Operation: During the warm season, solar radiation triggers the photothermal generator to heat the adsorbent, causing it to desorb and generate high-pressure working gas. The multi-functional acquisition box controls the opening of the solenoid valve, and the working gas enters the condensation section to release heat, liquefy, and fall into the evaporation section. During the warm season at night or when there is no sunlight, the adsorbent cools and generates adsorption negative pressure, causing the liquid ammonia in the evaporation section to boil under low pressure and actively absorb heat from the frozen soil. During the cold season, the adsorption bed is deeply cooled by extremely low temperatures to stimulate the limiting adsorption potential, enhance the low-temperature phase change heat transfer efficiency of liquid ammonia, and achieve synergistic dual-effect cooling of "active heat absorption in summer and enhanced heat dissipation in winter".

8. The application method according to claim 7, characterized in that, In step 3, the layout of the adsorption heat pipe group on the roadbed section is determined according to the yin-yang slope effect, the local prevailing wind direction, and the distribution characteristics of underground ice content. One or more topological structures are adopted, such as single-sided dense layout, quincunx staggered layout, slope inclined driving layout, or L-shaped horizontal buried pipe layout. The high thermal conductivity mud is prepared by mixing cement, bentonite, and graphite powder in a mass ratio of 1:0.2:0.1, and has a thermal conductivity ≥1.5 W / (m·K).

9. The application method according to claim 7, characterized in that, In step 5, the multi-functional acquisition box monitors the temperature and pressure of the composite adsorbent storage chamber and the evaporation section in real time, and automatically switches between the "desorption and energy storage" mode and the "evaporation and cooling" mode according to the day-night cycle and seasonal changes. At the same time, it automatically enhances the cooling depth of the adsorption bed according to the extremely low temperature conditions in the cold season, so as to achieve adaptive regulation under all climate conditions.

10. The application method according to claim 7, characterized in that, The method also includes step 6, long-term deformation control closed-loop feedback: the roadbed settlement and permafrost temperature data monitored in real time during step 5 are fed back to the cooling demand assessment model in step 1, and the adsorbent loading amount, heat rod group layout density and solenoid valve control threshold are iteratively optimized to form a full-chain deformation control closed loop of "exploration-design-layout-operation-feedback".

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