Intelligent self-maintenance and multi-mode visual ultralow-temperature frost heaving test system and intelligent self-maintenance and multi-mode visual ultralow-temperature frost heaving test method
By integrating an active thermal field programmable cooling head, a unidirectional freezing and multimodal visualization system, and an intelligent diagnostic and stepped thermal defrosting system, the problem of uncontrollability and unvisualization of existing freeze-heave test equipment at extremely low temperatures has been solved. This has enabled accurate simulation and visualization of the freeze-heave process, improving the operational reliability and data credibility of the equipment.
Patent Information
- Application Number
- CN202511460749.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-30
- Publication Date
- 2026-01-23
AI Technical Summary
Existing freeze-swell testing equipment cannot simulate extremely low temperature conditions at -120°C. The testing process is uncontrollable, key phenomena are not visible, the refrigeration system has poor reliability, and it is difficult to achieve high-fidelity freeze-swell testing.
It adopts an active thermal field programmable cooling head, a unidirectional freezing and multimodal visualization system, and an intelligent diagnostic and stepped thermo-fluorine defrosting system. Combined with multi-stage cascade refrigeration units and a two-dimensional thermoelectric semiconductor array, it achieves precise control and visualization of the freezing and swelling process, and integrates intelligent self-maintenance technology to ensure the efficient and reliable operation of the equipment.
It achieves accurate simulation and controllability of the freeze-heave process at -120℃, provides direct quantitative data for the study of freeze-heave mechanism, improves the success rate of the experiment and the reliability of the data, and ensures the long-term operational stability of the equipment.
Smart Images
Figure CN121385013A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of geotechnical engineering freezing test equipment, and particularly relates to an experimental system and method for simulating the frost heaving process of soil under-120℃ level extremely low temperature (such as liquid nitrogen freezing) conditions, and especially relates to a comprehensive experimental platform integrating efficient deep cooling, spatial heat flow fine modulation, intelligent self-maintenance, and multi-modal process visualization. BACKGROUND
[0002] Artificial freezing method is an important and effective reinforcement and water stopping method for underground engineering (such as subway connecting passages and tunnel entrances). In recent years, with the increase of engineering difficulty, liquid nitrogen freezing has been more and more applied in emergency rescue and special stratum reinforcement due to its advantages of fast refrigeration speed and strong freezing capacity. The boiling point of liquid nitrogen is-196℃, and the temperature of frozen soil formed in engineering usually reaches-120℃ or even lower extremely low temperature interval.
[0003] However, under the action of-120℃ level extremely low temperature, the frost heaving behavior of soil is essentially different from that under conventional salt water freezing (about-30℃), which is more severe in the frost heaving process, more complex in the growth mode of ice lens, and poses a greater threat to the safety of adjacent structures. Therefore, high-fidelity extremely low temperature artificial freezing heaving test is crucial for accurately predicting and controlling engineering risks.
[0004] The existing test technology for simulating the process has one or more of the following fundamental technical defects: Test temperature cannot be reached: Currently, commercial or conventional geotechnical engineering frost heaving test equipment mostly uses salt water circulation or conventional compressor refrigeration, and its limit temperature is usually above-60℃, which cannot simulate-120℃ level extremely low temperature working condition at all, resulting in that the test results cannot truly reflect the actual engineering behavior of extremely low temperature artificial freezing. Process uncontrollability: Direct use of liquid nitrogen for laboratory simulation makes it extremely difficult to accurately control the temperature and cooling rate, resulting in a violent and random test process, which cannot realize a repeatable, programmed slow or variable speed freezing process, and it is difficult to simulate a real and controlled engineering freezing scene. Key phenomena cannot be visualized: Traditional frost heaving test is a "black box" test. At extremely low temperature, key physical phenomena that determine the degree of frost heaving damage, such as the incubation, growth and spatial distribution of ice lens, cannot be directly observed and quantified. Reliability and efficiency problems of refrigeration system: In order to replace liquid nitrogen direct cooling, mechanical refrigeration systems developed at-120℃ deep cooling mostly use cascade refrigeration technology. However, they are prone to failure due to internal "ice blockage" at extremely low temperature, resulting in test interruption.
[0005] Therefore, the technical field urgently needs a new frost heaving test system that can accurately simulate the extremely low temperature artificial freezing process of-120 DEG C level, realize process active control, internal phenomenon visualization, and ensure long-term operation of high reliability. SUMMARY
[0006] The purpose of the present application is to provide a new type of ultra-low temperature artificial freezing frost heaving test system and its use method, which solves the core problems of process controllability, internal phenomenon visibility and equipment operation reliability of the existing artificial liquid nitrogen freezing technology through the systematic integration of multiple technologies.
[0007] To achieve the above purpose, the present application provides the following technical solutions:
[0008] The experimental system of the present application comprises an active thermal field programmable active thermal field programmable cooling head (1), a one-way freezing and multi-modal visualization system (2), and an intelligent diagnosis and stepwise thermal fluorine defrosting system (3).
[0009] The active thermal field programmable active thermal field programmable cooling head (1) is the core executive component of the present application, which realizes its unique function through the organic integration of two innovative hardware modules: -120 DEG C multi-stage self-recovery refrigeration unit (6) and two-dimensional thermoelectric semiconductor (TEC) array (7).
[0010] The active thermal field programmable active thermal field programmable cooling head (1) is the core executive component of the present application, which realizes its unique function through the organic integration of two innovative hardware modules: -120 DEG C multi-stage self-recovery refrigeration unit (6), which itself integrates intelligent defrosting, optimized refrigerant and multi-compressor collaborative control and other technologies to ensure its high efficiency, reliability and adjustability; and two-dimensional thermoelectric semiconductor (TEC) array (7). The one-way freezing and multi-modal visualization system (2) is the core observation component of the present application, which integrates optical imaging unit (22) and electrical tomography unit (23).
[0011] The collaborative controller (15) is responsible for collaborative scheduling of the cooling head and the visualization system, realizing the double closed-loop control of active guidance and intelligent maintenance.
[0012] The unit not only adopts multi-stage cascade in structure to achieve deep cooling of-120 DEG C, but also makes key innovations in the selection and matching of working medium-refrigerant. The present application proposes a three-stage cascade system optimized refrigerant formula:
[0013] High-temperature stage (e.g., operating at +30°C to -40°C): Employs a non-azeotropic refrigerant mixture with R290 (propane) and R600a (isobutane) as the main components. Both of these refrigerants are environmentally friendly hydrocarbon refrigerants with an ozone depletion potential (ODP) of 0 and an extremely low global warming potential (GWP). Their mixture exhibits excellent thermodynamic properties and a high latent heat of vaporization in this temperature range, providing efficient precooling for the next stage. Medium-temperature stage (e.g., operating at -40°C to -80°C): Employs a refrigerant mixture with R23 (trifluoromethane) and R14 (tetrafluoroethylene) as the main components. R23 is a mature medium- and low-temperature refrigerant, while the addition of a small amount of R14 effectively adjusts the phase change temperature glide of the mixture, making its refrigeration cycle in this temperature range closer to the ideal Lorentz cycle, thereby improving the COP. Low-temperature stage (e.g., operating at -80℃ to -120℃): A mixed refrigerant with R14 (carbon tetrafluoride) and nitrogen as the main components is used. R14 provides the basic cooling capacity in this temperature range, while the addition of a trace amount of high-pressure nitrogen serves two purposes. First, as a non-condensable gas, it can produce a more significant Joule-Thomson cooling effect after throttling, helping the system to break through lower temperatures. Second, it can effectively lower the freezing point of any trace moisture that may be present in the mixture, further reducing the risk of "ice blockage".
[0014] Through the above-mentioned "tailor-made" refrigerant selection and matching for different temperature zones, the refrigeration unit of this invention has a higher energy efficiency ratio and more stable operating pressure in the critical cryogenic range of -80℃ to -120℃ compared with traditional single mixed working fluid or conventional formula. At the same time, the unit still integrates intelligent diagnosis and stepped hot fluorine defrosting system (3) as the last line of defense to ensure long-term operation.
[0015] The beneficial effects of this invention lie in elevating traditional, uncontrollable artificial freezing simulation experiments at extremely low temperatures from a passive "observation mode" to an active "guided mode," allowing researchers to design and reproduce complex freeze-heave processes as needed. Through multimodal monitoring technology, the "black box" experiment is transformed into a "transparent" experiment, providing direct, quantitative, three-dimensional dynamic data for the study of freeze-heave mechanisms. Intelligent self-maintenance technology and multi-compressor configuration significantly improve the success rate and data reliability of simulated liquid nitrogen cryogenic freeze-heave experiments. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly explained below. Obviously, the described drawings are only a part of the embodiments of the present invention, and not all of them. Those skilled in the art can obtain other design schemes and drawings based on these drawings without creative effort. Figure 1 This is a schematic diagram of the overall test system. Figure 2 for Figure 1 Schematic diagram of a multi-stage self-cascaded cooling unit. Explanation of reference numerals in the attached diagram: 1. Active thermal field programmable cooling head; 2. Unidirectional freezing and multimodal visualization system; 3. Cooperative controller; 6. Multi-stage self-cascading refrigeration unit; 7. Two-dimensional thermoelectric semiconductor (TEC) array; 8. High-temperature stage refrigeration circuit; 9. Medium-temperature stage refrigeration circuit; 10. Low-temperature stage refrigeration circuit; 11. Heat exchanger; 13. Output cold plate; 17. Evaporator; 15. Intelligent diagnostic and stepped hot-fluid defrosting system; 14. Compressor; 18. First defrosting solenoid valve; 19. Second defrosting solenoid valve; 16. Bypass piping; 20. Defrosting heat exchanger; 21. Temperature sensor; 22. Optical imaging unit; 23. Electrical tomography imaging unit; 24. Acoustic phased array imaging unit. Detailed Implementation
[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0018] In a preferred embodiment, the unit employs a three-stage cascaded cycle, comprising a high-temperature stage refrigeration circuit (8), a medium-temperature stage refrigeration circuit (9), and a low-temperature stage refrigeration circuit (10). These three circuits are connected in series via a heat exchanger (11) and a gas-liquid separator. The evaporation side of the high-temperature stage circuit provides pre-cooling for the condensation side of the medium-temperature stage circuit, and the evaporation side of the medium-temperature stage circuit provides pre-cooling for the condensation side of the low-temperature stage circuit.
[0019] To achieve efficient regulation of cooling capacity and improve system redundancy, the unit is equipped with three independent, variable frequency driven compressors (14), which serve the three temperature level circuits mentioned above.
[0020] The coordinating controller (15) can coordinate the operation of the three compressors (14) according to experimental requirements or the instantaneous total heat load of the two-dimensional thermoelectric semiconductor (TEC) array (7).
[0021] During the initial rapid cooling phase of the experiment, all three compressors (14) operated at full power (highest frequency) to provide maximum cooling capacity.
[0022] When entering the heat preservation or slow freezing stage that requires precise control, the controller can selectively reduce the operating frequency of the low temperature stage or medium temperature stage compressor (14), or even temporarily shut it down when the heat load is extremely low, thereby achieving graded and large-scale adjustment of the cooling capacity.
[0023] Meanwhile, within each stage, the controller can also fine-tune the refrigerant flow rate of that stage by adjusting the electronic flow control valve connected in series in the refrigeration circuit of that stage, achieving continuous and smooth adjustment of the cooling capacity. This combined control strategy of "multi-compressor frequency conversion coarse adjustment + flow valve fine adjustment" enables wide-range and high-precision adjustment of the total refrigeration output power.
[0024] To improve energy efficiency, different, optimized and matched non-azeotropic refrigerants are preferred for each stage of the refrigeration circuit.
[0025] For example, the high-temperature stage refrigeration circuit (8) can use environmentally friendly hydrocarbon refrigerants with R290 and R600a as the main components; the medium-temperature stage refrigeration circuit (9) can use a mixture of R23 and R14; and the low-temperature stage refrigeration circuit (10) can use a mixture of R14 and nitrogen.
[0026] The end of the low-temperature stage refrigeration circuit (10) is an evaporator (17), whose output cold plate (13) forms the basic cooling interface of the cooling head.
[0027] To ensure long-term operational reliability, the system integrates an intelligent diagnostic and stepped hot-fluorine defrosting system (3).
[0028] The intelligent diagnostic and stepped hot-fluorine defrosting system (3) mainly consists of a bypass pipeline (16) connected between the outlet of the compressor (14) and the inlet of the evaporator (17), a defrosting solenoid valve connected in series on the pipeline, and a temperature sensor (21) installed at the outlet of the evaporator (17).
[0029] The co-controller (15) monitors the signal from the temperature sensor (21) and automatically opens the corresponding defrosting solenoid valve once it detects a potential risk of freezing and blockage (e.g., the temperature is below a preset threshold or the rate of change is abnormal).
[0030] In a preferred embodiment, the intelligent diagnostic and stepped thermo-thermal defrosting system (3) also includes a defrosting heat exchanger (20). By selectively allowing defrosting gas to flow through the heat exchanger (11), two-stage heating of the evaporator (17)—either "mild" or "powerful"—is achieved, i.e., stepped defrosting.
[0031] The two-dimensional thermoelectric semiconductor (TEC) array (7), as a fine modulation module, consists of multiple (e.g., arranged in a 32x32) Peltier thermoelectric units tightly integrated on the output cold plate (13) of the evaporator (17) of the multi-stage self-cascading refrigeration unit (6).
[0032] In a preferred embodiment, its specific construction is as follows:
[0033] First, in terms of material selection and structural design, the output cold plate (13) is preferably made of dispersion-strengthened oxygen-free copper (DS-Cu) material. The two-dimensional thermoelectric semiconductor (TEC) array (7) consists of multiple specially customized low-temperature optimized Peltier thermoelectric units based on bismuth telluride (Bi2Te3) and doped with antimony (Sb) or selenium (Se), which are encapsulated between ceramic substrates.
[0034] Secondly, regarding the core interface coupling technology, to address the enormous shear stress caused by the mismatch in thermal expansion coefficients between the two materials under a vast temperature difference from room temperature to -120°C, they are coupled through a multi-layered composite flexible high thermal conductivity interface material. The structure of this interface material, from bottom to top, consists of: a 0.1mm thick annealed indium foil; and a layer of low-temperature thermally conductive silicone grease filled with boron nitride nanoparticles.
[0035] The entire two-dimensional thermoelectric semiconductor (TEC) array (7) is positioned by a precision frame made of titanium alloy with a certain degree of elasticity and is subjected to a uniform and constant preload by a set of disc springs.
[0036] This multi-layered, flexible thermal conduction coupling method ensures efficient heat transfer from the output cold plate (13) to the cold end of the two-dimensional thermoelectric semiconductor (TEC) array (7) (interfacial thermal resistance is less than 0.05 K·cm). 2 This design effectively decouples and buffers thermal stress, ensuring the long-term operational reliability of the core component.
[0037] The co-controller (15) outputs an adjustable PWM control current independently to each Peltier unit in the array via a multi-channel programmable DC power supply.
[0038] The multimodal visualization frost heave test chamber (3) is the core observation component for achieving process transparency. It adopts a top-unidirectional freezing test mode.
[0039] Its visualization sample tube is made of high-strength polycarbonate material, with an inner diameter of 200 mm and a height of 500 mm. The sample (preferably a transparent soil with a refractive index matching the target soil) is placed inside the tube.
[0040] The bottom of the sample cylinder is a freely movable porous piston, the displacement of which is measured by a laser displacement sensor below to record the total frost heave.
[0041] The system integrates three complementary monitoring units:
[0042] Its optical imaging unit (22) includes two synchronously triggered high-resolution CCD cameras, symmetrically arranged on both sides of the visualization sample tube, and equipped with a uniform LED surface light source, for imaging tracer particles inside the sample tube. This unit is mainly used to acquire two-dimensional or quasi-three-dimensional particle displacement fields and pore water migration velocity fields.
[0043] Its electrical tomography unit (23) includes multiple rings (e.g., 8 rings, 32 per ring) of flexible electrode strips arranged at equal intervals along the outer wall of the visualization sample tube, forming an ERT / ECT sensor array. This unit utilizes the significant differences in the electrical properties of ice and water, and is mainly used for real-time, three-dimensional reconstruction of the macroscopic morphology of the frozen edge and the spatial distribution and ice content of ice lenses.
[0044] In a more preferred embodiment, an acoustic phased array imaging unit (24) is also included. This unit comprises multiple ultrasonic phased array probes arranged around the outer wall of the sample cylinder. Because ultrasound is extremely sensitive to acoustic impedance interfaces, this unit can perform high-resolution imaging of the fine structure of a single ice lens and the microcrack network caused by freezing with a precision far exceeding that of electrical tomography.
[0045] The collaborative controller (15) is an integrated industrial PC or PXI platform. The proprietary software running on it implements the core logic of the cryogenic frost heave test method described in this invention, and its core algorithm module includes:
[0046] Data Acquisition and Multimodal Fusion Module: This module is responsible for real-time acquisition of raw data from the aforementioned optical, electrical, and acoustic imaging units. The software's built-in data fusion algorithm preferably employs an asynchronous data fusion framework based on Kalman filtering, fusing data from different sensors and sampling rates into a unified spatiotemporal coordinate system to estimate a three-dimensional field variable vector describing the current state of the sample in real time.
[0047] Closed-loop guided control module: Its core is the Model Predictive Control (MPC) algorithm. Users set a four-dimensional (3D space + time) evolution target that evolves over time via the software interface. Within a fixed control cycle, this module iteratively executes the following steps: state prediction, optimization solution, control sequence generation, and execution.
[0048] Intelligent maintenance collaborative logic: The above-mentioned guidance control process and intelligent defrosting logic run in parallel. When the defrosting program is triggered, the guidance control algorithm will immediately enter the "disturbance compensation mode" and actively adjust the output of the TEC array according to the preset physical model to minimize the interference of the defrosting process on the sample temperature field.
[0049] Through the above specific implementation methods, the present invention systematically integrates efficient and reliable cryogenic technology, high-precision heat flow modulation technology, and advanced process visualization technology, providing a powerful and reliable comprehensive experimental platform for the scientific research of cryogenic frost heave testing.
Claims
1. An intelligent self-maintenance and multimodal visualization ultra-low temperature freeze-thaw test system, characterized in that, include: An active thermal field programmable cooling head (1) is used to apply spatially modulated ultra-low temperature cooling to a sample; a unidirectional freezing and multimodal visualization system (2) is used to carry the sample and perform three-dimensional real-time monitoring of its internal freezing process; an intelligent diagnostic and stepped thermal defrosting system (3) is used to form a closed-loop control loop with the active thermal field programmable cooling head (1) and the unidirectional freezing and multimodal visualization system (2).
2. The system according to claim 1, characterized in that, The active thermal field programmable cooling head (1) includes: a multi-stage self-cascading cooling unit (6) configured to generate a base cold source at -120°C or lower; and a two-dimensional thermoelectric semiconductor (TEC) array (7) thermally integrated onto the output cold plate (13) of the active thermal field programmable cooling head (1).
3. The multi-stage self-cascaded cooling unit (6) according to claim 2, characterized in that, include: A high-temperature stage refrigeration circuit (8), a medium-temperature stage refrigeration circuit (9), and a low-temperature stage refrigeration circuit (10) are connected in series via a heat exchanger (11). The low-temperature stage refrigeration circuit (10) includes a final-stage evaporator (17), the shell of which forms the output cold plate (13). Each of the high-temperature stage refrigeration circuit (8), the medium-temperature stage refrigeration circuit (9), and the low-temperature stage refrigeration circuit (10) is equipped with a compressor (14). Furthermore, the high-temperature stage refrigeration circuit (8) and the low-temperature stage refrigeration circuit (10) use different, optimized, and matched non-azeotropic refrigerants to improve the refrigeration efficiency in the cryogenic range of -80°C to -120°C.
4. The system according to claim 1, characterized in that, Includes an intelligent diagnostic and stepped hot-fluorine defrosting system (3) integrated with the multi-stage self-cascade refrigeration unit (6) and controlled by a co-controller (15); the intelligent diagnostic and stepped hot-fluorine defrosting system (3) includes: at least one bypass line (16), one end of which is connected to the output end of the at least one compressor (14) and the other end of which is connected to the input end of the evaporator (17); a first defrosting solenoid valve (18) and a second defrosting solenoid valve (19), which are disposed in the bypass line (16). 6) Above; a defrost heat exchanger (20) connected in series with a portion of the bypass line (16) and located between the first defrost solenoid valve (18) and the second defrost solenoid valve (19); a temperature sensor (21) disposed on the outlet line of the evaporator (17); wherein the co-controller (15) is configured to achieve staged heating of the evaporator (17) by selectively opening the first defrost solenoid valve (18) or the second defrost solenoid valve (19).
5. The cooperative controller (15) according to claim 4, characterized in that, It is configured to: adjust the total cooling capacity of the basic cold source output by the multi-stage self-cascading cooling unit (6) by adjusting the operating parameters of multiple compressors (14) in the multi-stage self-cascading cooling unit (6) according to experimental requirements or the total heat load of the two-dimensional thermoelectric semiconductor (TEC) array (7) in the active thermal field programmable cooling head (1); at the same time, process the data from the electrical tomography imaging unit (23) and the acoustic phased array imaging unit (24) in the unidirectional freezing and multimodal visualization system (2) through a data fusion algorithm to identify and quantify the dynamic three-dimensional morphology of the freezing edge and the spatial distribution of ice lenses; and process the data from the optical imaging unit (22) through an image processing algorithm to calculate the particle displacement field and the pore water migration velocity field.
6. The cooperative controller (15) according to claim 5 executes a multi-objective control algorithm, characterized in that, The control objectives of the algorithm include one or a combination of the following: actively shaping a preset freezing front morphology; inducing the formation of ice lenses at one or more preset spatial locations inside the sample.
7. The system according to claim 1, characterized in that, The system’s unidirectional freezing and multimodal visualization system (2) includes: an optical imaging unit (22) configured to photograph the sample tube; an electrical tomography imaging unit (23) with a sensor array arranged on the outer wall of the sample tube; and an acoustic phased array imaging unit (24).