Liquid nitrogen artificial frozen soil experimental device

Abstract

The utility model relates to a kind of liquid nitrogen artificial frozen soil experimental device, comprising: liquid nitrogen supply unit, for providing liquid nitrogen cold source, experimental body, experimental body includes sample container and liquid nitrogen cavity, sample container is used to contain soil sample, liquid nitrogen cavity is set below sample container and is thermally connected with the bottom of sample container, provides cold end for soil sample, temperature control unit, between liquid nitrogen supply unit and the liquid nitrogen cavity of experimental body, temperature control unit is configured to automatically regulate liquid nitrogen transported to liquid nitrogen cavity, laser displacement sensor, fixedly set in the upper of sample container, for measuring the frost heaving displacement of soil sample;Through the automatic regulation of liquid nitrogen flow, the bottleneck that temperature reduction process is uncontrollable, difficult to maintain stable temperature gradient in the prior art is solved, the laser displacement sensor above sample container, eliminate the inherent defects that contact type measuring device is easy to freeze, jam under extremely low temperature environment, realize the continuous, accurate and reliable measurement of frost heaving displacement.

Description

Technical Field

[0001] This utility model relates to the field of cryogenic engineering technology, specifically to a liquid nitrogen artificial frozen soil experimental device. Background Technology

[0002] Artificial ground freezing technology, especially rapid freezing methods using liquid nitrogen as a cold source, has significant research value and application prospects in geotechnical and cryogenic engineering. Accurately simulating and studying the process and laws of liquid nitrogen freezing of soil in the laboratory is key to advancing this technology.

[0003] However, constructing a device capable of achieving a controllable and stable experimental environment in the liquid nitrogen temperature range presents severe challenges, and existing technical solutions have limitations in the core components that constitute a complete experimental system.

[0004] In terms of automated and precise control of the cold source, existing experimental devices generally lack effective means of regulating liquid nitrogen, an extremely low-temperature medium. Most devices cannot automatically and precisely adjust the flow rate and pressure of liquid nitrogen during the gradual cooling process, making it difficult to maintain a stable predetermined cooling rate, and even more difficult to flexibly establish and maintain different temperature gradients at different freezing stages. This limitation in cooling process control directly restricts the systematic study of the dynamic relationship between frost heave and temperature gradient.

[0005] In the design of cold energy transfer in the experimental body, existing devices often fail to achieve efficient, unidirectional conduction of cold energy from the source to the sample. Poor design of the thermally conductive connection between the cold source and the bottom of the sample container, or the existence of significant radial cold energy leakage, makes it difficult to form a stable temperature field along the sample axis. The experimental conditions are not sufficiently similar to the real underground environment, affecting the accuracy and reliability of the research results.

[0006] In terms of reliable measurement of critical data, extremely low temperatures pose a significant obstacle to traditional measurement methods. Widely used contact displacement sensors are prone to freezing and sticking in liquid nitrogen temperatures, leading to severe distortion or even interruption of frost heave displacement measurement data. This measurement bottleneck makes obtaining continuous and accurate frost heave-time curves exceptionally difficult.

[0007] In summary, existing technologies are limited by systemic problems such as insufficient automated temperature control, poor cold conduction paths, and inaccurate measurements at extremely low temperatures. They lack a complete solution that integrates a controllable cold source, a highly efficient cold-conducting body, and a reliable measurement unit. Therefore, there is an urgent need in this field for a novel experimental device that can overcome these limitations, particularly in achieving controllable, stable, and accurate measurements in the liquid nitrogen temperature range. Utility Model Content

[0008] To address the shortcomings of existing technologies, this invention provides a liquid nitrogen artificial frozen soil experimental device, aiming to solve one or more of the problems mentioned in the background technology.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: a liquid nitrogen artificial frozen soil experimental device, comprising: a liquid nitrogen supply unit for providing a liquid nitrogen cold source; an experimental body, the experimental body including a sample container and a liquid nitrogen chamber, the sample container for holding a soil sample, the liquid nitrogen chamber being disposed below the sample container and thermally connected to the bottom of the sample container to provide a cold end for the soil sample; a temperature control unit connected between the liquid nitrogen supply unit and the liquid nitrogen chamber of the experimental body, the temperature control unit being configured to automatically adjust the liquid nitrogen supplied to the liquid nitrogen chamber; and a laser displacement sensor fixedly disposed above the sample container for measuring the frost heave displacement of the soil sample.

[0010] Furthermore, the experimental body also includes an insulation structure, which is placed between the liquid nitrogen chamber and the sample container to reduce the transfer of liquid nitrogen cooling energy to the sample container.

[0011] Furthermore, the insulation structure includes an insulation sleeve disposed between the liquid nitrogen chamber and the sample container; a channel is formed inside the insulation sleeve that communicates with the internal chamber of the sample container, and the bottom of the sample is located within the channel of the insulation sleeve.

[0012] Furthermore, the insulation structure also includes multiple insulation bolts that pass through the insulation sleeve and connect and fix the sample container to the support or liquid nitrogen chamber.

[0013] Furthermore, it also includes a support rod base, with the liquid nitrogen chamber located on top of the support rod base.

[0014] Furthermore, it also includes a mounting flange and multiple support rods, with the lower end of the support rods connected to a support rod seat and the upper end connected to the mounting flange, so that the mounting flange is supported directly above the sample container; the laser displacement sensor is mounted on the mounting flange.

[0015] Furthermore, the temperature control unit includes a gas-liquid separator, and an inlet regulating valve, an exhaust regulating valve, and a drain regulating valve, which are respectively connected to the gas-liquid separator; the temperature control unit is configured to automatically adjust the flow rate and pressure of liquid nitrogen entering the liquid nitrogen chamber by coordinating the opening of the inlet regulating valve, the exhaust regulating valve, and the drain regulating valve, thereby achieving control of the cooling rate of the soil sample.

[0016] Furthermore, multiple temperature sensor mounting holes are provided along the axial direction on the side wall of the sample container, and the multiple temperature sensors are installed in the mounting holes one by one.

[0017] Furthermore, the temperature control unit also includes a controller, with inlet regulating valve, vent regulating valve, drain regulating valve, and multiple temperature sensors electrically connected to the controller. The controller is configured to: receive signals from the temperature sensors to obtain real-time temperature data of the soil sample, compare the real-time temperature data with a preset temperature program, and control the flow rate and pressure of liquid nitrogen entering the liquid nitrogen chamber by coordinating the opening of the inlet regulating valve, vent regulating valve, and drain regulating valve, thereby achieving automatic control of the cooling rate of the soil sample. Furthermore, the controller is configured to execute the following control logic: when the real-time temperature data is higher than the target value of the preset temperature program, increase the opening of the liquid inlet regulating valve and / or decrease the opening of the exhaust regulating valve to increase the cooling supply; when the real-time temperature data is lower than the target value of the preset temperature program, decrease the opening of the liquid inlet regulating valve and / or increase the opening of the exhaust regulating valve, and / or open the drain regulating valve to reduce the cooling supply.

[0018] The liquid nitrogen artificial frozen soil experimental device described in this utility model has the following advantages: by automatically adjusting the liquid nitrogen flow rate, it solves the bottleneck of uncontrollable cooling process and difficulty in maintaining a stable temperature gradient in the prior art. The laser displacement sensor located above the sample container eliminates the inherent defects of contact measuring devices that are prone to freezing and jamming in extremely low temperature environments, and realizes continuous, accurate and reliable measurement of frost heave displacement. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present utility model; Figure 2 This is a schematic diagram of the experimental body of an embodiment of this utility model.

[0020] Explanation of reference numerals in the attached drawings: 1: Liquid nitrogen tank; 2: Gas-liquid separator; 21: Exhaust regulating valve; 22: Liquid inlet regulating valve; 23: Liquid outlet regulating valve; 31: Mounting bracket; 32: Sample container; 33: Soil sample; 34: Insulation bolt; 35: Insulation sleeve; 36: Liquid nitrogen chamber; 37: Liquid inlet pipe; 38: Support base; 39: Support rod base; 40: Exhaust pipe; 41: Support rod; 42: Mounting flange; 43: Laser displacement sensor. Detailed Implementation

[0021] Typical embodiments embodying the features and advantages of this utility model will be described in detail in the following description. It should be understood that this utility model can have various variations in different embodiments, all of which do not depart from the scope of this utility model, and the descriptions and illustrations therein are for illustrative purposes only and not intended to limit this utility model.

[0022] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0023] To further illustrate the principle and structure of this utility model, the preferred embodiments of this utility model will now be described in detail with reference to the accompanying drawings.

[0024] like Figure 1-2 As shown in the figure, this utility model embodiment provides a liquid nitrogen artificial frozen soil experimental device, the core of which is to solve the problems of controllability, stability and accurate measurement of frozen soil frost heave experiment in the liquid nitrogen temperature range.

[0025] The system configuration of the device is as follows: it includes a liquid nitrogen supply unit as the basis of the cold source, an experimental body for realizing the transfer of cold energy and holding the soil sample 33, a temperature control unit for precisely regulating the cold source, and a laser displacement sensor 43 for non-contact measurement of frost heave.

[0026] Specifically, the liquid nitrogen supply unit is a standard Dewar flask-type liquid nitrogen tank 1. The outlet of the liquid nitrogen tank 1 is equipped with a cryogenic manual valve and is connected to a subsequent temperature control unit via a metal bellows or insulated hose to provide a pure and stable flow of liquid nitrogen.

[0027] Furthermore, the experimental body is the core platform for performing the freezing experiment. This body includes a sample container 32 for holding the soil sample 33. The sample container 32 is preferably a cylindrical structure made of a material with low thermal conductivity (such as polytetrafluoroethylene or specific engineering plastics) to minimize horizontal cold loss. Multiple threaded holes are uniformly formed along the axial direction (i.e., the height direction) of the side wall of the sample container 32 as temperature sensor mounting holes for installing thermocouples or platinum resistance thermometers to monitor the temperature gradient of the soil sample 33 from top to bottom in real time.

[0028] Furthermore, a liquid nitrogen chamber 36 is disposed directly below the sample container 32. The liquid nitrogen chamber 36 is made of metal, and its top plane is in close contact with the bottom plane of the sample container 32, thereby achieving efficient heat conduction and providing a stable and uniform cold end for the soil sample 33.

[0029] Furthermore, the liquid nitrogen chamber 36 is provided with an inlet pipe 37 and an exhaust pipe 40 communicating with its interior. One end of the inlet pipe 37 is connected to the side or bottom of the liquid nitrogen chamber 36, and the other end of the inlet pipe 37 is connected to the liquid output end of the temperature control unit (i.e., the gas-liquid separator 2), forming a liquid nitrogen delivery path.

[0030] Furthermore, one end of the exhaust pipe 40 is connected to the top of the liquid nitrogen chamber 36 to discharge the nitrogen gas that has been vaporized after absorbing heat. The other end of the exhaust pipe 40 can be connected to the atmosphere or an exhaust gas treatment device. The arrangement of the exhaust pipe 40 ensures stable pressure within the liquid nitrogen chamber 36 and prevents gas accumulation from affecting the entry of liquid nitrogen and heat exchange efficiency.

[0031] Furthermore, to achieve unidirectional axial conduction of cold energy and prevent radial leakage of cold energy through mechanical connections, a thermal insulation structure is provided between the liquid nitrogen chamber 36 and the sample container 32. The core of this thermal insulation structure is an thermal insulation sleeve 35 made of G10 composite material.

[0032] Furthermore, the insulating sleeve 35, the liquid nitrogen chamber 36, and the sample container 32 are arranged in a stacked manner along the axial direction, forming a "sandwich" structure. Specifically, the liquid nitrogen chamber 36 is located at the bottom layer, the insulating sleeve 35 is directly stacked on top of the liquid nitrogen chamber 36, and the sample container 32 is stacked on top of the insulating sleeve 35.

[0033] Furthermore, the insulating sleeve 35 has a channel extending through its upper and lower end faces at its center. This channel is directly connected to the internal chamber of the upper sample container 32, with the bottom of the sample located within the channel of the insulating sleeve. The wall of the insulating sleeve 35 is made of G10 insulating material and is positioned between the liquid nitrogen chamber 36 and the side wall of the sample container 32. Due to the extremely low thermal conductivity of G10 material, this wall effectively blocks the radial transfer of cold energy from the liquid nitrogen chamber 36 to the side wall of the sample container 32, thereby ensuring that most of the cold energy is conducted upwards through the central channel and axially to the soil sample 33 via the bottom of the sample container 32, achieving unidirectional cold energy conduction.

[0034] Furthermore, the sample container 32 is fixedly connected to the liquid nitrogen chamber 36 below by multiple heat-insulating bolts 34. While providing a robust mechanical connection, its own heat-insulating properties prevent the formation of metal cold bridges, further enhancing the heat insulation effect of the entire connection area.

[0035] Furthermore, to enhance the overall insulation effect, the assembled sample container 32, liquid nitrogen chamber 36, and insulation sleeve 35 are all wrapped with flexible insulation material to form an insulation layer, such as ultrafine glass wool or aerogel felt, to further isolate heat exchange with the environment.

[0036] Furthermore, the support system of the experimental body is divided into three parts: lower, middle, and upper. The lower support is a solid support base 38 that directly contacts the experimental platform, providing a stable foundation for the entire device.

[0037] Furthermore, a support rod 41 seat 39 is provided above the support base 38. The liquid nitrogen chamber 36 is directly placed on top of the support rod 41 seat 39 via its own heat-insulating base, thereby obtaining stable support.

[0038] Furthermore, the upper part of the support system is an independent measuring bracket, consisting of a mounting flange 42 and multiple support rods 41. The lower ends of these support rods 41 are connected to the support rod 41 seat 39, and the upper ends are connected to the mounting flange 42. This design ensures that the mounting flange 42 is stably supported directly above the sample container 32 without any direct contact with the sample container 32 itself, thus constructing a stable and independent optical measuring platform above the sample container 32, effectively avoiding vibration interference or heat conduction caused by mechanical contact.

[0039] Furthermore, the temperature control unit is crucial for achieving automated experiments. This unit primarily consists of a gas-liquid separator 2, whose inlet is connected to a liquid nitrogen supply unit via a pipeline. Three key components are installed on the gas-liquid separator 2: an inlet regulating valve 22 connecting to an external liquid nitrogen source, an exhaust regulating valve 21 for releasing gaseous nitrogen to regulate internal pressure, and a drain regulating valve 23 for discharging excess liquid nitrogen. All three regulating valves are electrically controllable cryogenic vacuum bellows valves (CV valves).

[0040] Furthermore, the temperature control unit also includes a core controller. This controller can be a PLC, an industrial computer, or a high-performance microcontroller. The controller establishes an electrical connection via cables to the three regulating valves for liquid inlet, liquid outlet, and liquid outlet, as well as to all temperature sensors installed on the sample container 32.

[0041] Furthermore, the controller is programmed to implement closed-loop control. Its workflow is as follows: the controller internally stores a preset temperature program. During the experiment, it continuously receives signals from various temperature sensors and calculates the real-time average temperature or specific point temperature of soil sample 33. Then, it compares this real-time temperature data with the target value in the preset program.

[0042] Based on the above comparison results, the controller executes the following cooperative control logic: When the real-time temperature is higher than the target value, the controller outputs a signal to increase the opening of the liquid inlet regulating valve 22 to increase the liquid nitrogen supply, and may simultaneously decrease the opening of the exhaust regulating valve 21 to increase the pressure inside the gas-liquid separator 2, working together to enhance the refrigeration power.

[0043] When the real-time temperature is lower than the target value, the controller outputs a signal to reduce the opening of the liquid inlet regulating valve 22 and may simultaneously increase the opening of the exhaust regulating valve 21 to reduce pressure. In cases of excessively rapid cooling, the controller will also open the drain regulating valve 23 to quickly discharge excess liquid nitrogen from the system, thereby rapidly reducing the input of cooling capacity. Through this coordinated control of the three valves, precise and stable automatic adjustment of the cooling rate of the soil sample 33 is achieved.

[0044] Furthermore, the measurement system of the device consists of two parts: displacement measurement and temperature measurement.

[0045] Displacement measurement is performed by a high-precision laser displacement sensor 43. This sensor is fixed to the upper mounting flange 42 via a finely adjustable mounting bracket 31. By adjusting the radial and vertical position of the bracket, the laser beam of the laser displacement sensor 43 can be vertically aligned and focused on the center of the top surface of the soil sample 33 inside the sample container 32, thereby achieving real-time, non-contact, high-precision measurement of frost heave displacement.

[0046] Temperature measurements are performed using a set of temperature sensors (such as thermocouples or platinum resistance thermometers). These sensors are not directly embedded inside the soil sample 33, but are inserted one-to-one into axially oriented temperature sensor mounting holes on the side wall of the sample container 32 from the outside, with the sensor's measuring tip in direct contact with the side surface of the soil sample 33 inside the hole. This arrangement accurately senses the temperature of the soil sample 33 at different heights while avoiding placing the sensor body inside the soil sample 33, thus completely eliminating the risk of sensor damage caused by frost heave and ensuring minimal interference with the natural deformation process of the soil sample 33.

[0047] The device operates as follows: First, soil sample 33 is loaded and all sensors are connected. The user sets the desired cooling program on the controller. After the device is started, liquid nitrogen, under the precise control of the controller, is transported from the gas-liquid separator 2 to the liquid nitrogen chamber 36 via the inlet pipe 37. The liquid nitrogen vaporizes and absorbs heat in the chamber, transferring the cooling energy to the soil sample 33 through the bottom of the sample container 32. The vaporized nitrogen is then discharged from the system through the exhaust pipe 40. Throughout this process, the controller coordinates the adjustment of each valve to ensure that the actual cooling curve closely follows the preset program. Simultaneously, the laser displacement sensor 43 continuously records the frost heave height of the soil sample 33, and the temperature sensor group records the temperature field changes, thereby synchronously obtaining the correlation data between the frost heave amount and the temperature gradient.

[0048] This invention's temperature control unit, through automatic adjustment of liquid nitrogen flow rate, solves the core bottleneck of uncontrollable cooling process and difficulty in maintaining a stable temperature gradient in existing technologies. The bottom heat-conducting connection design between the liquid nitrogen chamber 36 and the sample container 32 in the experimental body, combined with an insulation structure, ensures efficient and unidirectional transfer of cold energy to the soil sample 33, effectively simulating real freezing conditions and preventing cold energy loss. Furthermore, the laser displacement sensor 43 located above the sample container 32 completely eliminates the inherent defects of contact measuring devices in extremely low-temperature environments, such as easy freezing and jamming, achieving continuous, accurate, and reliable measurement of frost heave displacement. In summary, this device provides a complete and reliable technical solution for the controllable, stable, and accurate study of frost heave behavior in frozen soil within the liquid nitrogen temperature range.

[0049] The above description is merely a preferred embodiment of the present utility model and does not constitute any limitation on the technical scope of the present utility model. Therefore, any minor modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present utility model shall still fall within the scope of the technical solution of the present utility model.

Claims

1. A liquid nitrogen artificial frozen soil experimental device, characterized in that, include: Liquid nitrogen supply unit, used to provide liquid nitrogen cold source; The experimental body includes a sample container and a liquid nitrogen chamber. The sample container is used to hold soil samples, and the liquid nitrogen chamber is located below the sample container and is thermally connected to the bottom of the sample container to provide a cold end for the soil samples. A temperature control unit is connected between the liquid nitrogen supply unit and the liquid nitrogen chamber of the experimental body. The temperature control unit is configured to automatically regulate the liquid nitrogen supplied to the liquid nitrogen chamber. A laser displacement sensor is fixedly installed above the sample container to measure the frost heave displacement of the soil sample.

2. The liquid nitrogen artificial frozen soil experimental device according to claim 1, characterized in that, The experimental body also includes an insulation structure, which is placed between the liquid nitrogen chamber and the sample container to reduce the transfer of liquid nitrogen cooling to the sample container.

3. The liquid nitrogen artificial frozen soil experimental device according to claim 2, characterized in that, The insulation structure includes an insulation sleeve, which is positioned between the liquid nitrogen chamber and the sample container; a channel is formed inside the insulation sleeve that communicates with the internal chamber of the sample container, and the bottom of the sample is located within the channel of the insulation sleeve.

4. The liquid nitrogen artificial frozen soil experimental device according to claim 3, characterized in that, The insulation structure also includes multiple insulation bolts that pass through the insulation sleeve and connect and fix the sample container to the support or liquid nitrogen chamber.

5. The liquid nitrogen artificial frozen soil experimental device according to claim 1, characterized in that, It also includes a support rod base, with the liquid nitrogen chamber located on top of the support rod base.

6. The liquid nitrogen artificial frozen soil experimental device according to claim 5, characterized in that, It also includes a mounting flange and multiple support rods. The lower end of the support rod is connected to the support rod seat, and the upper end is connected to the mounting flange, so that the mounting flange is supported directly above the sample container; the laser displacement sensor is mounted on the mounting flange.

7. The liquid nitrogen artificial frozen soil experimental device according to claim 1, characterized in that, The temperature control unit includes a gas-liquid separator, and an inlet regulating valve, an exhaust regulating valve, and a drain regulating valve, which are respectively connected to the gas-liquid separator. The temperature control unit is configured to automatically adjust the flow rate and pressure of liquid nitrogen entering the liquid nitrogen chamber by coordinating the opening of the inlet regulating valve, the exhaust regulating valve, and the drain regulating valve, thereby controlling the cooling rate of the soil sample.

8. The liquid nitrogen artificial frozen soil experimental device according to claim 7, characterized in that, Multiple temperature sensor mounting holes are provided along the axial direction on the side wall of the sample container, and the multiple temperature sensors are installed in the mounting holes one by one.

9. The liquid nitrogen artificial frozen soil experimental device according to claim 8, characterized in that, The temperature control unit also includes a controller, an inlet regulating valve, an exhaust regulating valve, a drain regulating valve, and multiple temperature sensors, all of which are electrically connected to the controller. The controller is configured to receive signals from the temperature sensors to obtain real-time temperature data of the soil sample, compare the real-time temperature data with a preset temperature program, and control the flow rate and pressure of liquid nitrogen entering the liquid nitrogen chamber by coordinating the opening of the inlet regulating valve, the exhaust regulating valve, and the drain regulating valve, thereby achieving automatic control of the cooling rate of the soil sample.

10. The liquid nitrogen artificial frozen soil experimental device according to claim 9, characterized in that, The controller is configured to execute the following control logic: when the real-time temperature data is higher than the target value of the preset temperature program, increase the opening of the liquid inlet regulating valve and / or decrease the opening of the exhaust regulating valve to increase the cooling supply; when the real-time temperature data is lower than the target value of the preset temperature program, decrease the opening of the liquid inlet regulating valve and / or increase the opening of the exhaust regulating valve, and / or open the drain regulating valve to reduce the cooling supply.

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