Underground heat storage-frozen soil hydrothermal coupling performance test experiment system

Abstract

The invention belongs to the field of geotechnical engineering thermal-mechanical coupling experiment systems, and particularly relates to a buried heat storage-frozen soil hydrothermal coupling performance test experiment system. A magnet, a gradient unit and a radio frequency coil are utilized to form a nuclear magnetic resonance imaging assembly, and on the premise that a frozen soil structure is not disturbed, the structure of the frozen soil is optimized; high-resolution imaging is carried out on temperature distribution, moisture migration and pore evolution in the frozen soil; the time sequence of the magnetic field, the gradient field and the radio frequency pulse is accurately controlled through the control unit, the interaction process between the heat storage water body in the frozen soil and the freeze-thaw interface can be dynamically captured, the heat transfer path and the water vapor migration behavior are synchronously analyzed, and the temporal-spatial resolution and consistency of experimental data are improved; the corrugated pipe is connected with the constant-temperature bath to simulate the freeze-thaw environment of frozen soil, the external heat preservation cabin and a water source provided by the Markov bottle are matched, the dual control conditions of cold and hot disturbance and water supply are achieved, and the long-term disturbance and response mechanism of a heat storage system to the hot and humid state of the frozen soil in actual engineering is effectively simulated.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of geotechnical engineering thermal coupling experiment system, and particularly relates to a buried heat storage-frozen soil water-heat coupling performance test experiment system. BACKGROUND

[0002] The buried heat storage water body is a key technical branch of the solar photo-thermal energy storage system, and heat storage is achieved by burying the geomembrane water storage pool underground. However, the high thermal conductivity of the geomembrane easily causes heat loss of the heat storage water body, which leads to changes in the temperature field in the surrounding frozen soil, drives the migration of unfrozen water or water vapor in the soil and the degradation of the pore structure, and seriously threatens the long-term stability of the geothermal energy storage project in cold regions. Therefore, it is urgent to build an experimental system that can solve the coupling mechanism of the water-heat response of frozen soil, the migration of unfrozen water and the evolution of pores under the thermal disturbance of the heat storage water body.

[0003] The existing frozen soil water vapor migration monitoring technology at least has the following shortcomings: first, the destructive detection method, such as the sampling drying method, collects frozen soil samples and dries and weighs to calculate the unfrozen water content, although the principle is mature, but it destroys the original structure of the soil and cannot obtain the dynamic migration data of the unfrozen water in the freezing and thawing process; second, the non-destructive detection method includes time domain reflectometry (TDR) and neutron scattering method, TDR relies on the soil dielectric constant to invert the water, which is greatly affected by soil texture and salt content, and it is difficult to accurately quantify the unfrozen water; the neutron scattering method has radiation safety risks and cannot simultaneously represent the evolution of the pore structure; third, the nuclear magnetic resonance detection device, the patent CN 117147611A (Zhou Fengxi) discloses a low-field nuclear magnetic resonance technology, which can non-destructively analyze the rock and soil pore water distribution through the relaxation time (T2 spectrum), but the existing device is aimed at static core samples, and does not integrate the buried heat storage water body heat loss simulation module and the cold region freezing and thawing environment reproduction unit, which cannot meet the whole-process coupling experiment demand of "heat storage-frozen soil-water-heat-nuclear magnetic monitoring". SUMMARY

[0004] The purpose of the present application is to overcome the problem that the existing technology cannot reproduce the double complex boundaries of the freezing and thawing cycle in cold regions and the heat storage disturbance, cannot simultaneously analyze the coupling mechanism of the heat transfer, pore evolution and water vapor migration of frozen soil, and provides a buried heat storage-frozen soil water-heat coupling performance test experiment system.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: In a first aspect, the present application provides a buried heat storage-frozen soil water-heat coupling performance test experimental system, which comprises an external heat preservation cabin, a magnet and a soil box body are arranged in the external heat preservation cabin, frozen and thawed soil is contained in the soil box body, the frozen and thawed soil has a heat storage water body, the soil box body is wrapped with a corrugated pipe, the corrugated pipe is connected with a constant temperature bath, a radio frequency coil is arranged outside the corrugated pipe, a gradient unit is arranged on the inner surface of the magnet, the gradient unit faces the soil box body, a marangoni bottle is arranged outside the external heat preservation cabin, the marangoni bottle is connected into the frozen and thawed soil through a pipeline, a temperature and humidity sensor is arranged in the soil box body, the magnet, the gradient unit and the radio frequency coil are connected with a control unit, the control unit is used for controlling the magnet to generate a magnetic field, controlling the gradient unit to generate a gradient field, controlling the radio frequency coil to emit a radio frequency pulse and receiving a back wave, the control unit is connected with an image system, the image system is used for image reconstruction according to the data sent by the control unit, and the signal quality detection and the analysis result of image distortion are fed back to the control unit.

[0006] The present application further improves that the temperature and humidity sensors are vertically and equidistantly arranged in the soil box body.

[0007] The present application further improves that the inner wall of the soil box body is attached with an EPDM rubber elastic buffer pad.

[0008] The present application further improves that the heat storage water body comprises a water storage box body, a cylindrical recess with a shape matched with the water storage box body is arranged in the frozen and thawed soil, the water storage box body is arranged in the cylindrical recess, and a water body top cover is arranged on the top of the water storage box body.

[0009] The present application further improves that a clamping groove support is arranged outside the soil box body, the clamping grooves of the clamping groove support are equidistantly arranged along the vertical direction of the box body, arc-shaped supporting blocks are arranged in the clamping grooves, and the corrugated pipes are fixed on the arc-shaped supporting blocks in the clamping grooves in a serpentine arrangement mode.

[0010] The present application further improves that the soil box body is placed on a bottom plate, and the bottom plate is placed on the bottom surface of the external heat preservation cabin through a support.

[0011] The present application further improves that the external heat preservation cabin is made of a non-magnetic high molecular material closed-cell polyurethane foam board.

[0012] The present application further improves that the heat storage water body is in a circular truncated cone shape, and the cross-sectional area of the top of the heat storage water body is greater than that of the bottom.

[0013] The present application further improves that the heat storage water body is in an inverted pyramid shape, and the cross-sectional area of the top of the heat storage water body is greater than that of the bottom.

[0014] The present application further improves that the heat storage water body is in a circular cylinder shape.

[0015] Compared with the prior art, the present application has the following beneficial effects: The application utilizes a magnet, a gradient unit and a radio frequency coil to form a nuclear magnetic resonance imaging (MRI) assembly, so that high-resolution imaging of the internal temperature distribution, water migration and pore evolution of frozen soil is realized without disturbing the structure of the frozen soil. The time sequence of the magnetic field, the gradient field and the radio frequency pulse is accurately controlled by a control unit, so that the system can dynamically capture the interaction process between the heat storage water body and the freezing-thawing interface in the frozen soil, thereby synchronously analyzing the heat transfer path and the water vapor migration behavior, and significantly improving the spatial and temporal resolution and consistency of the experimental data. The application simulates the freezing and thawing environment of the frozen soil through a corrugated pipe connected to a constant temperature bath, and provides a water source through an external insulation cabin and a Mariotte bottle, thereby realizing the dual control conditions of cold and hot disturbance and water supply, and effectively simulating the long-term disturbance and response mechanism of the heat and moisture state of the frozen soil in the heat storage system in the actual project. This setting breaks through the limitation that multiple disturbance and long-term cycle conditions cannot be considered in traditional experimental methods. The application sets up temperature and humidity sensors, so that the micro image data and the macro sensing and monitoring data are complementary to each other, and the multi-scale collaborative observation ability in the experimental process is enhanced. The linkage design of the control unit and the image system enables the image quality detection and distortion analysis feedback to optimize the radio frequency pulse and the magnetic field parameters in real time, improves the imaging accuracy and the experimental reliability, and further supports the quantitative identification of the frozen soil structure change under the multi-cycle freezing and thawing process. In summary, the application not only realizes the visualization and quantifiable analysis of the heat-water-vapor multi-field coupling behavior of the frozen soil-heat storage system under complex boundary conditions, but also has a high degree of automation and intelligent control ability, thereby providing a reliable, accurate and representative experimental platform for studying the stability of the cold region foundation, the utilization of underground heat energy and the evolution mechanism of the frozen soil. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 FIG. 1 is a structural schematic diagram of the application; Figure 2 FIG. 2 is a schematic diagram of the inverted pyramid-shaped heat storage water body in the application; Figure 3 FIG. 3 is a detailed schematic diagram of the inverted pyramid-shaped heat storage water body in the application; Figure 4 FIG. 4 is a three-dimensional schematic diagram of the inverted pyramid-shaped heat storage water body in the application; Figure 5 FIG. 5 is a detailed schematic diagram of the heat exchanger arrangement in the application; Figure 6 FIG. 6 is a detailed diagram of the heat exchanger arrangement in the application; Figure 7 FIG. 7 is a schematic diagram of the top cover of the inverted pyramid-shaped heat storage water body in the application; Figure 8 FIG. 8 is a cross-sectional view of the cylindrical heat storage water body in the application; Figure 9 FIG. 9 is a horizontal cross-sectional view of the first heat storage water body provided in embodiment 1 of the application; Figure 10a A second horizontal sectional view of the heat storage water body provided for the embodiment 2 of the present application; Figure 10b A second schematic view of the heat storage water body provided for the embodiment 2 of the present application; Figure 11 A third horizontal sectional view of the heat storage water body provided for the embodiment 3 of the present application; Figure 12a A top view of the cylindrical experimental platform provided for the embodiment 4 of the present application; Figure 12b A front view of the cylindrical experimental platform provided for the embodiment 4 of the present application; In the figure: 1, external insulation cabin; 2, electric heater; 3, magnet; 4, gradient unit; 5, radio frequency coil; 6, soil box; 601, EPDM rubber elastic buffer pad; 7, freeze-thaw soil; 701, cylindrical groove; 8, heat storage water body; 801, water body top cover; 8011, non-metallic bolt; 802, water storage box; 9, corrugated pipe; 10, clamping groove support; 1001, arc-shaped supporting block; 11, constant temperature bath; 12, temperature and humidity sensor; 13, marangoni bottle; 14, data acquisition instrument; 15, bottom plate; 16, support; 17, control unit; 18, image system; 19, computer. DETAILED DESCRIPTION

[0017] For further understanding of the present application, the present application is described in detail below in combination with the drawings and specific embodiments. It should be understood that the embodiments are merely for the purpose of explanation and not limitation.

[0018] Reference is made to Figure 1 , Figure 2 and Figure 9The application relates to a buried heat storage-frozen soil water-heat coupling performance test experimental system, which comprises an external heat preservation cabin 1, a magnet 3 and a soil box 6 built in the external heat preservation cabin 1, frozen and thawed soil 7 loaded in the soil box 6, a heat storage water body 8 in the frozen and thawed soil 7, a corrugated pipe 9 wrapped outside the soil box 6, the corrugated pipe 9 connected with a constant temperature bath 11, a radio frequency coil 5 arranged outside the corrugated pipe 9, a gradient unit 4 arranged on the inner surface of the magnet 3 and facing the soil box 6, a marangoni bottle 13 arranged outside the external heat preservation cabin 1 and connected with the frozen and thawed soil 7 through a pipeline, a temperature and humidity sensor 12 arranged in the soil box 6, the magnet 3, the gradient unit 4 and the radio frequency coil 5 all connected with a control unit 17, the control unit 17 used for controlling the magnet 3 to generate a magnetic field, controlling the gradient unit 4 to generate a gradient field, controlling the radio frequency coil 5 to emit a radio frequency pulse and receive a back wave, the control unit 17 connected with an image system 18, the image system 18 used for image reconstruction according to the data sent by the control unit 17 and feeding back signal quality detection and image distortion analysis results to the control unit 17, and all the data in the soil box 6 collected by a data acquisition instrument 14 and sent to a computer 19.

[0019] In use, the control unit 17 is started, and experimental parameters such as a freezing and thawing cycle, a heat storage temperature, water disturbance intensity and the like are set. The constant temperature bath is heated or refrigerated, a temperature field is transmitted to the outer wall of the soil box through the corrugated pipe, and the heat disturbance of the underground heat storage device to the frozen soil under different environmental conditions is simulated. The external heat preservation cabin provides a stable thermal boundary environment and prevents external environmental interference. The frozen and thawed soil and the heat storage water body are prearranged in the soil box, water is quantitatively injected through the marangoni bottle, and the water content state of the frozen soil is regulated and controlled. The constant temperature bath is controlled to stably apply heat flow disturbance through the corrugated pipe, so that heat transfer, water migration and phase change processes (freezing-melting) occur in the soil, and a dynamic disturbance boundary is formed. The control unit starts the magnet, the gradient unit and the radio frequency coil to generate a static magnetic field, a spatial gradient field and a radio frequency pulse sequence, so that the hydrogen protons in the frozen soil generate nuclear magnetic resonance signals. The system receives the echo signal and transmits it to the image system, which is used for reconstructing the temperature, water distribution and pore structure images in the frozen soil. The temperature and humidity sensor in the soil box collects the internal environmental parameters of the frozen soil in real time, and cooperates with the imaging data of the image system to form multi-source data. Through unified scheduling of the control unit, the time sequence of each sensing module is synchronized, so that the whole process data of the frozen soil evolution at different time nodes is obtained. The image system reconstructs the received echo data to form a three-dimensional image, analyzes the heat transfer path, water vapor migration trend and pore change morphology. Meanwhile, the system detects the image signal quality and distortion degree in real time, and feeds back the results to the control unit, realizes dynamic adjustment of the radio frequency parameters and the gradient field, and optimizes the subsequent imaging effect. The control unit records the temperature field, water field and structure evolution information in each freezing and thawing cycle. The experiment can simulate multiple freezing and thawing cycles according to requirements, records the continuous disturbance and response, and studies the cumulative evolution law of the frozen soil under the long-term freezing and thawing and heat storage action.

[0020] The application can solve the problems of non-destructive dynamic monitoring of water vapor migration process of frozen soil under the operation condition of buried heat storage water body and the problem of accurate reproduction of freeze-thaw cycle boundary conditions, and can realize visual monitoring of water vapor migration and pore evolution under temperature gradient driving.

[0021] Embodiment 1: Referring to Figure 1 and Figure 2 , the embodiment increases the freeze-thaw soil 7 in the soil box 6, the soil box 6 is made of acrylic plate, the temperature and humidity sensors 12 are vertically and equidistantly arranged in the soil box 6, and the inner wall of the soil box 6 is attached with an EPDM rubber elastic buffer pad 601, so that the lateral stress generated by the frost heaving of the frozen soil can be absorbed to prevent the cracking of the box. The soil box 6 is provided with a water permeable hole at the bottom, and the pipe of the mason jar 13 is connected to the soil box 6 through the water permeable hole.

[0022] Referring to Figure 3 , Figure 7 and Figure 8 , the heat storage water body 8 is in a cylindrical shape, the freeze-thaw soil 7 is provided with a cylindrical recess 701, and the bottom of the acrylic water storage box 802 is mounted in the cylindrical recess 701. The water storage box 802 is made of acrylic, and the cylindrical recess 701 can facilitate the installation of the water storage box 802. The water storage box 802 includes an upper open cavity, and the heat storage water body 8 can be installed in the cavity. The heat storage water body 8 includes the water storage box 802, the freeze-thaw soil 7 is provided with a cylindrical recess 701 matched with the shape of the water storage box 802, the water storage box 802 is arranged in the cylindrical recess 701, and the water storage box 802 is provided with a water body top cover 801 at the top. The water body top cover 801 is fixed on the water storage box 802 by a non-metallic bolt 8011.

[0023] Referring to Figure 5 and Figure 6 , the corrugated pipe 9 is fixed on the prefabricated clamping groove support 10 on the side of the freeze-thaw soil box 6 in a serpentine arrangement, the clamping grooves of the clamping groove support 10 are equidistantly arranged along the vertical direction of the box, the arc-shaped supporting blocks 1001 are arranged in the clamping grooves, and the two ends of the corrugated pipe 9 are connected to the medium inlet and outlet of the high and low temperature constant temperature bath 11 through quick plug sealing joints. The corrugated pipe 9 is made of polytetrafluoroethylene, and the clamping groove support 10 is made of wood.

[0024] The control unit 17 cooperates with the magnet 3, the gradient unit 4, the radio frequency coil 5 and the image system 18, and the control unit 17 issues precise timing instructions. The magnet 3 maintains a stable main magnetic field according to the instructions, the gradient unit 4 generates a gradient field according to the instructions of the control unit, and the spatial positioning of the imaging micro area is realized by the time and space coding of the gradient pulse; the radio frequency coil 5 transmits radio frequency pulses to excite spins and receive echo signals carrying physical information of the detected object under the timing control of the control unit. The signal is amplified, filtered and digitized, and then transmitted to the image system. The image system 18 completes signal acquisition and image reconstruction, and simultaneously feeds back the results of signal quality detection and image distortion analysis to the control unit 17; the control unit 17 further adjusts the active shimming module of the magnet 3 and the eddy current compensation circuit of the gradient unit 4 based on the feedback, so that the instruction scheduling of the control unit 17, the main magnetic field construction of the magnet 3, the spatial coding of the gradient unit 4, the excitation and reception of the radio frequency coil 5, and the signal processing and feedback optimization of the image system 18 form a closed-loop cooperation.

[0025] Referring to Figure 4 The bottom plate 15 and the support 16 are made of non-magnetic wooden materials. The bottom plate 15 and the clamping groove support 10 made of non-magnetic wooden materials can reduce the influence on the experimental results.

[0026] The external thermal insulation cabin 1 is made of a thermal insulation cabin body made of non-magnetic high polymer material closed-cell polyurethane foam board, and the magnet 3 of the nuclear magnetic resonance monitoring unit is kept at a distance greater than 150 mm. This not only improves the stability of the temperature gradient field, but also avoids magnetic field interference, ensuring the accuracy of nuclear magnetic signal acquisition.

[0027] Embodiment 2 Referring to Figure 10a Figure 10b The present embodiment is based on the above-mentioned embodiments, and provides a heat storage water body 8 in the shape of a circular truncated cone. The cross-sectional area of the top of the circular truncated cone-shaped heat storage water body 8 is greater than that of the bottom. The structure of the circular truncated cone-shaped heat storage water body 8, which is large at the top and small at the bottom, can greatly improve the heat transfer efficiency, thereby improving the heat storage efficiency of the heat storage water body.

[0028] Embodiment 3 Referring to Figure 11 The present embodiment is based on the above-mentioned embodiments, and provides a heat storage water body 8 in the shape of an inverted pyramid, and the cross-sectional area of the top is greater than that of the bottom. The frozen and thawed soil 7 is provided with an inverted pyramid-shaped groove, and the bottom of the inverted pyramid-shaped acrylic water storage tank body 802 is installed in the groove. The setting of the groove can facilitate the installation of the inverted pyramid-shaped acrylic water storage tank body 802.

[0029] Embodiment 4 Referring to Figure 12a and Figure 12bThe embodiment is improved on the basis of the above-mentioned embodiment, a serpentine bellows 9 is laid around the cylindrical heat storage water body 8 in the top of the frozen and thawed soil 7, the double complex boundary of the frozen and thawed cycle and heat storage disturbance in the cold region is reproduced to a great extent, so that the problems that the prior art cannot carry out nondestructive monitoring of water vapor migration under the heat storage disturbance working condition, cannot accurately reproduce the double complex boundary in the cold region, and cannot quantify the water-heat coupling mechanism of frozen soil are solved.

[0030] The present application optimizes the shortcomings that the existing experimental device cannot reproduce the double complex boundary of the frozen and thawed cycle and heat storage disturbance in the cold region, cannot synchronously analyze the coupling mechanism of heat transfer, pore evolution and water vapor migration of frozen soil by the cooperation of the heat storage-frozen soil coupling unit, the environment simulation unit, the nuclear magnetic resonance monitoring unit and the control and data processing unit; the heat storage water body is embedded in the frozen and thawed soil carrier to reproduce the heat loss scene of the buried heat storage, the high and low constant temperature bath and the marsden bottle are used to build the heat and moisture boundary of the frozen and thawed cycle in the cold region, and the nuclear magnetic resonance monitoring unit dynamically scans the water vapor migration and pore evolution of frozen soil in a non-contact manner. The design can effectively solve the problems that the prior art cannot carry out nondestructive monitoring of water vapor under the heat storage disturbance working condition, cannot accurately reproduce the double complex boundary in the cold region, and cannot quantify the water-heat coupling mechanism of frozen soil, and provides experimental basis and theoretical support for the research of geothermal energy storage and frost heaving prevention and control in the cold region.

[0031] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced, without departing from the spirit and scope of the present application, any modification or equivalent replacement, which should be covered in the protection scope of the claims of the present application.

Claims

1. A buried heat storage-permafrost water-heat coupling performance test experimental system, characterized in that, The application relates to an external heat preservation cabin (1), wherein a magnet (3) and a soil box (6) are arranged in the external heat preservation cabin (1), the soil box (6) is filled with frozen and thawed soil (7), the frozen and thawed soil (7) is provided with a heat storage water body (8), the soil box (6) is wrapped with a corrugated pipe (9), the corrugated pipe (9) is connected with a constant temperature bath (11), the corrugated pipe (9) is provided with a radio frequency coil (5) outside, the inner surface of the magnet (3) is provided with a gradient unit (4) which faces the soil box (6), a marinsky bottle (13) is arranged outside the external heat preservation cabin (1) and is connected with the frozen and thawed soil (7) through a pipeline, a temperature and humidity sensor (12) is arranged in the soil box (6), the magnet (3), the gradient unit (4) and the radio frequency coil (5) are connected with a control unit (17), the control unit (17) is used for controlling the magnet (3) to generate a magnetic field, controlling the gradient unit (4) to generate a gradient field, controlling the radio frequency coil (5) to emit a radio frequency pulse and receive a back wave, the control unit (17) is connected with an image system (18), the image system (18) is used for image reconstruction according to the data sent by the control unit (17) and feeds back the analysis results of signal quality detection and image distortion to the control unit (17).

2. The buried heat storage-permafrost water-heat coupling performance test experimental system according to claim 1, characterized in that, The temperature and humidity sensor (12) is vertically and equidistantly arranged in the soil box (6).

3. The buried heat storage-frozen soil water-heat coupling performance test experimental system according to claim 1, characterized in that, An EPDM rubber elastic buffer pad (601) is attached to the inner wall of the soil box (6).

4. The test system according to claim 1, wherein, The heat storage water body (8) comprises a water storage box (802), a cylindrical recess (701) with a shape matched with the water storage box (802) is arranged in the frozen and thawed soil (7), the water storage box (802) is arranged in the cylindrical recess (701), and a water body top cover (801) is arranged at the top of the water storage box (802).

5. The buried heat storage-frozen soil water heat coupling performance test experimental system according to claim 1, characterized in that, The soil box (6) is provided with a clamping groove support (10), clamping grooves of the clamping groove support (10) are equidistantly arranged along the vertical direction of the box, arc-shaped supporting blocks (1001) are arranged in the clamping grooves, and the corrugated pipe (9) is fixed on the arc-shaped supporting blocks (1001) in a serpentine arrangement.

6. The buried heat storage-permafrost water-heat coupling performance test experimental system according to claim 1, characterized in that, The soil box (6) is placed on a bottom plate (15), and the bottom plate (15) is placed on the bottom surface of the external heat preservation cabin (1) through a support (16).

7. The buried heat storage-permafrost water-heat coupling performance test experimental system according to claim 1, characterized in that, The external heat preservation cabin (1) is made of non-magnetic high polymer material closed-cell polyurethane foam board.

8. The test system according to claim 1, wherein, The heat storage water body (8) is in the shape of a circular truncated cone, the cross-sectional area of the top of the heat storage water body (8) is larger than that of the bottom.

9. The buried heat storage-permafrost water-heat coupling performance test experimental system according to claim 1, characterized in that, The heat storage water body (8) is in the shape of an inverted pyramid, the cross-sectional area of the top of the heat storage water body (8) is larger than that of the bottom.

10. The test system according to claim 1, wherein, The heat storage water body (8) is in the shape of a cylinder.

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