An ultra-low temperature open frost heave experimental system and experimental method

Abstract

The invention discloses an ultra-low temperature open frost heave experimental system and an experimental method, comprising a refrigeration device, which comprises a refrigeration component; a sample box, wherein a top cover is provided at the top opening, and the bottom of the inner cavity of the sample box is covered with a bottom plate, the bottom plate can slide up and down along the inner wall of the sample box, the refrigeration component is arranged on the top cover, and the cooling structure of the refrigeration component is directly opposite to the inner cavity of the sample box; a clamping device, which has a clamping end that can be adjusted up and down, and the clamping end can press the top cover and the sample box to each other; a frost heave amount measuring device, which is fixed to the sample box, and the frost heave amount measuring device is provided with a telescopic measuring end, the measuring end extends upward and always abuts against the bottom plate. The invention clamps the top cover and the sample box in advance through the clamping end, and the clamped top cover limits the expansion direction of the sample, so that the sample can only expand downward and squeeze the bottom plate, and the displacement of the bottom plate drives the displacement of the measuring end, and the frost heave strain of the rock and soil body can be obtained by detecting the position change of the measuring end.

Description

Technical Field

[0001] The invention relates to the technical field of experimental equipment for studying open frost heaving processes of rock, soil, concrete, asphalt and the like, and in particular to an ultra-low temperature open frost heaving experimental system and an experimental method. Background Art

[0002] In engineering practice, rock and soil bodies are usually in an open frost heave system with a significant temperature gradient. However, existing open frost heave research mainly focuses on weak low temperature (temperature greater than -50°C) and slow freezing (temperature drop less than 10°C / day), ignoring the ultra-low temperature (temperature less than or equal to -50°C) and variable-speed frost heave problems in emergency engineering mechanics. Different from the natural temperature in ordinary cold regions, ultra-low temperature environments will affect the water migration process of rock and soil. At the same time, the degree of progress of frost heave disasters and the different means of disaster relief lead to different frost heave rates of rock and soil. Therefore, it is extremely necessary to build an open frost heave simulation test device with ultra-low temperature and variable freezing rate. Summary of the invention

[0003] The purpose of the present invention is to provide an ultra-low temperature open frost heave experimental system and experimental method to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0004] The solution of the present invention to solve its technical problem is:

[0005] A super-low temperature open frost heave experiment system comprises: a refrigeration device, which comprises a refrigeration component; a sample box, wherein a top cover is provided at the top opening of the sample box, the bottom of the inner cavity of the sample box is covered with a bottom plate, and the bottom plate can slide up and down along the inner wall of the sample box, the refrigeration component is arranged on the top cover, and the cooling structure of the refrigeration component is directly opposite to the inner cavity of the sample box; a clamping device, which has a clamping end that can be adjusted up and down, and the clamping end can press the top cover and the sample box against each other; a frost heave measurement device, which is fixed to the sample box, and the frost heave measurement device is provided with a retractable measuring end, and the measuring end extends upward and always abuts against the bottom plate.

[0006] The technical solution has at least the following beneficial effects: the top cover is covered at the top opening of the sample box, the rock and soil sample is placed on the bottom plate and located in the inner cavity of the sample box, the external water replenishment device is interconnected with the inner cavity of the sample box, so as to realize the water replenishment of the sample. During the experiment, the refrigeration component works and provides an ultra-low temperature environment for the inner cavity of the sample box. The water in the rock and soil sample is easy to freeze and expand in the ultra-low temperature environment, so that the volume of the sample expands. The experimenter clamps the top cover and the sample box in advance through the pressing end to reduce the occurrence of the sample lifting the top cover, reduce water loss, and enhance the cold preservation effect. At the same time, the pressed top cover limits the expansion direction of the sample, so that the sample can only expand downward and squeeze the bottom plate, causing the bottom plate to slide downward along the inner wall of the sample box. At this time, the frost heave measuring device and the sample box are relatively fixed, and the displacement of the bottom plate drives the displacement of the measuring end. By detecting the position change of the measuring end, the frost heave strain of the rock and soil can be obtained, which provides convenience for analyzing the different freezing rates of the sample.

[0007] As a further improvement of the above technical solution, the refrigeration device includes at least two stages of refrigeration units, the refrigeration unit includes a circulation channel and a refrigeration element, the circulation channel includes a cooling section and a heat transfer section, the hot surface of the refrigeration element faces the heat transfer section of the same refrigeration unit, and the cold surface of the refrigeration element faces the cooling section of the refrigeration unit of the next level, the refrigeration element is the refrigeration element of the lowest level refrigeration unit, and the cooling structure of the refrigeration element is the cold surface of the refrigeration element. The refrigerant circulates in the circulation channel of a refrigeration unit, and the external refrigeration device absorbs the heat of the refrigerant in the cooling section of the uppermost circulation channel. The cooled refrigerant is transferred to the heat transfer section and flows through the hot surface of the refrigeration element. The cold surface temperature of the refrigeration element is lower than its own hot surface temperature, so that the heat transfer section of the next-level circulation channel exchanges heat with the cold surface of the refrigeration element, ensuring that the refrigerant temperature of the next-level circulation channel is always lower than the refrigerant temperature of the upper-level circulation channel, and multi-stage refrigeration is realized layer by layer. The lowest-level refrigeration element, that is, the refrigeration part, is set on the top cover, and its cold surface faces the inner cavity of the sample box, so as to ultra-low temperature freeze the samples in the sample box, which is convenient for building an ultra-low temperature, variable freezing rate open frost heave simulation and observation test system for rock and soil, and accurately constructing the frost heave model in cold region engineering, which is of great significance for the study of moisture migration under rapid ultra-low temperature cooling conditions.

[0008] As a further improvement of the above technical solution, the circulation channel of the refrigeration unit at the lowest level can be switched and connected to the circulation channel of any upper refrigeration unit. The circulation channel of the refrigeration unit at the terminal can be combined with the circulation channel of any upper refrigeration unit to form a new circulation channel, so that the temperature of the refrigerant introduced can be changed, the temperature span of the hot surface of the refrigeration component can be changed, and the cooling structure of the refrigeration component can adjust the temperature range of the inner cavity of the sample box to a larger range, thereby improving the experimental effect and the application range of the experiment.

[0009] As another improvement of the above technical solution, the present invention further comprises a bracket, the sample box is placed on the bracket, the clamping device is arranged on the bracket, the pressing end is located above the top cover, and the pressing end can move downward and press on the top cover. The sample box and the bracket are relatively positioned, and the experimenter can directly control the degree of compression between the top cover and the sample box by adjusting the upper and lower positions of the pressing end, which is convenient and quick, and will not affect the water supply process of the external water adding device, thereby reducing interference.

[0010] As a further improvement of the above technical solution, the clamping device includes an adjusting rod, which is arranged in the up and down directions. The upper end of the adjusting rod is threadedly connected to the bracket, and the lower end of the adjusting rod is the clamping end. At least two of the adjusting rods are circumferentially arranged around the center line of the sample box. The frost heave measuring device includes at least two dial indicators, which are circumferentially arranged around the center line of the base plate. The dial indicator includes an indicator disk and a measuring rod. The indicator disk and the sample box are relatively fixed. The measuring rod is telescopically connected to the indicator disk, and the measuring end is the measuring rod. The experimenter can adjust the upper and lower positions of the clamping end by turning the adjustment rod, which is convenient for adjustment. There are at least two adjustment rods, which are arranged circumferentially around the center of the sample box to improve the clamping stability of the clamping end and play a role in uniform force, reducing the occurrence of lifting of the top cover during the frost heave of rock and soil, ensuring that the experiment can be carried out smoothly in an ultra-low temperature environment. The indicator disk and the sample box are relatively fixed. The sample expands and squeezes the bottom plate in an ultra-low temperature environment. The bottom plate slides downward along the inner wall of the sample box, and the bottom plate drives the measuring end to move. The experimenter can directly obtain the position change of the bottom plate by observing the data of the indicator disk, and the frost heave strain of the rock and soil body can be obtained from this. The experimenter can observe the freezing rate of different samples under the same environment, or the freezing rate of the same sample under different environments, which is convenient for data acquisition and improves the experimental effect.

[0011] As another improvement of the above technical solution, the present invention also includes a water adding device, the water adding device includes a measuring cylinder and a water pipe, the measuring cylinder is arranged on the bracket, one end of the water pipe is connected to the bottom opening of the measuring cylinder, and the other end of the water pipe is connected to the plurality of the permeable through holes and connected to the bottom surface of the bottom plate. The water pipe and the measuring cylinder are connected to form a communicating vessel, and when the liquid level in the measuring cylinder is higher than the bottom plate, the bottom plate is automatically replenished with water, and the liquid level in the measuring cylinder is adjusted to control the continuous and stable water source on the top surface of the bottom plate. At the same time, the amount of water and the rate of water migration can be read on the measuring cylinder, which is convenient for the experimenter to record and improve the experimental effect.

[0012] As a further improvement of the above technical solution, the sample box includes a left cover and a right cover, one end of the left cover is hinged to one end of the right cover, the other end of the left cover is magnetically connected to the other end of the right cover, the left cover and the right cover are covered with each other to form a box body, the top cover is magnetically connected to the top of the box body and covers the top opening of the box body, and the clamping device also includes an enclosure, which is sleeved on the outer wall of the box body. When the rock and soil samples need to be replaced, the experimenter directly breaks open one end of the magnetic connection between the left cover and the right cover. The left cover and the right cover can rotate relative to each other, so that the inner cavity of the box is completely opened. The experimenter can directly take out the sample placed on the bottom plate, and the sample box can be replaced without completely disassembling the sample box, reducing the process of reinstallation and wiring, facilitating the direct replacement of samples, and improving the experimental efficiency. At the same time, the sample box and the top cover are connected by magnetic suction, so that the bottom surface of the top cover and the top surface of the sample box are in close contact, which is also convenient for disassembly and alignment installation, making it easy for the experimenter to replace the sample in the sample box and achieve rapid disassembly and assembly. At the same time, different types of sample boxes can be easily replaced for different experimental purposes to meet the experimental requirements. During the experiment, the enclosure can prevent the rock and soil from frost heaving and propping up the left and right covers, thereby improving the stability of the experiment.

[0013] The present invention also provides a low-temperature open frost heave test method, comprising the above-mentioned ultra-low-temperature open frost heave test system, comprising the following steps:

[0014] S1. Load the sample into the sample box, adjust the clamping end of the clamping device so that the clamping end presses the top cover onto the sample box, fix the frost heave measuring device relatively to the sample box, and place the retractable measuring end against the bottom surface of the bottom plate;

[0015] S2, the refrigeration device comprises at least two stages of refrigeration units, the refrigeration units comprise circulation channels, refrigeration elements, temperature sensors and temperature adjustment modules, the circulation channels comprise cooling sections and heat transfer sections, in any two adjacent stages of the refrigeration units, the hot surface of the refrigeration element of the upper stage refrigeration unit faces the heat transfer section of the same stage, the cold surface of the refrigeration element faces the cooling section of the lower stage refrigeration unit, the refrigeration element of the lower stage refrigeration unit is the refrigeration element, the refrigeration element is arranged on the top cover, and the cold surface of the refrigeration element faces the inner cavity of the sample box, the temperature sensor can detect the temperature of the cooling section and the heat transfer section, the temperature adjustment module is connected to the refrigeration element, and the temperature sensor and temperature adjustment module of each stage refrigeration unit are connected to the control module;

[0016] S3, a water supply device supplies water to the sample in the inner cavity of the sample box;

[0017] S4, the control module converts the received expected value into a first control signal, and then sends the first control signal to the temperature adjustment modules of the refrigeration units at each level. After receiving the first control signal, the temperature adjustment module adjusts the refrigeration temperature and refrigeration rate of the refrigeration elements at the same level. The control module receives the actual value periodically detected by the temperature sensor, and the control module compares the actual value with the expected value and converts it into a second control signal. The second control signal is used to drive the temperature adjustment module to adjust the refrigeration temperature and refrigeration rate of the refrigeration elements at the same level.

[0018] The technical solution has at least the following beneficial effects: the present invention builds a multi-stage refrigeration system, based on the Peltier effect of the refrigeration element, using the upper stage refrigeration to create a working environment temperature for the next stage refrigeration, creating an ultra-low temperature working environment for the sample in the sample box, and at the same time, after the user inputs the expected value, that is, the target temperature and the target time, into the computer, the computer converts the data into a first control signal and transmits it to the control module, and after the temperature adjustment module receives the first control signal, it adjusts the refrigeration temperature and the refrigeration rate of the refrigeration unit, and at the same time, after periodically receiving the measured value fed back by the temperature sensor, the measured value and the expected value are compared and analyzed and converted into a second control signal , driving the temperature adjustment module to continuously adjust the working state of the refrigeration element, realizing the adjustment of the terminal refrigeration temperature and rate, completing the closed loop, ensuring that the temperature value in the sample box and the time to reach the temperature value are as close to and maintained as possible to the expected value output by the user, and the temperature adjustment module can achieve the change of the refrigeration effect of the refrigeration element by adjusting the voltage signal. The present invention can control the temperature and cooling rate of the ultra-low temperature environment in the inner cavity of the sample box, so that an ultra-low temperature, variable freezing rate open frost heave simulation and observation test system for rock and soil bodies can be built, the experimental effect can be improved, and the frost heave model in cold region engineering can be accurately constructed, which is of great significance for the study of moisture migration under rapid ultra-low temperature cooling conditions.

[0019] As a further improvement of the above technical solution, the circulation channel of each refrigeration unit is provided with an on-off valve, and the circulation channel of the lowest refrigeration unit is provided with an inflow control valve and an outflow control valve. Except for the circulation channels of the lowest refrigeration unit, all circulation channels are connected to the inflow control valve and the outflow control valve. The inflow control valve, the outflow control valve and the plurality of through-section valves are connected to the refrigerant shunt controller. The refrigerant shunt controller is connected to the control module. After receiving the expected value, the control module sends a switching signal to the refrigerant shunt controller, so that the corresponding through-section valve, the inflow control valve and the outflow control valve are opened or closed, so that the circulation channel of the lowest refrigeration unit can be switched and connected to the circulation channel of any upper refrigeration unit. The control module analyzes and judges the expected value and selects different refrigeration effects. The circulation channel of the terminal refrigeration unit can be combined with the circulation channel of any upper refrigeration unit to form a new circulation channel, so that the temperature of the refrigerant introduced can be changed, the temperature span of the hot surface of the refrigeration unit is changed, and the cooling structure of the refrigeration unit can adjust the temperature range of the inner cavity of the sample box to a larger range, thereby improving the experimental effect and the application range of the experiment.

[0020] As a further improvement of the above technical solution, the refrigeration units include a room temperature refrigerant refrigeration unit, a first-stage refrigeration unit, a second-stage refrigeration unit and a third-stage refrigeration unit at the lowest level. When the control module receives the expected value, it satisfies: the expected value is within the threshold range of 0°C to -20°C, the refrigerant shunt controller receives the switching signal and controls the on-off valves of the room temperature refrigerant refrigeration unit and the third-stage refrigeration unit to be disconnected, the inlet control valve and the outflow control valve are opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the room temperature refrigerant refrigeration unit form a new refrigerant circulation channel; the expected value is within the threshold range of -20°C to -40°C , the refrigerant shunt controller receives the switching signal and controls the on-off valves of the first-stage refrigeration unit and the third-stage refrigeration unit to be disconnected, the inflow control valve and the outflow control valve to be opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the first-stage refrigeration unit form a new refrigerant circulation channel; the expected value is within the threshold range of -40℃ to -70℃, the refrigerant shunt controller receives the switching signal and controls the on-off valves of the second-stage refrigeration unit and the third-stage refrigeration unit to be disconnected, the inflow control valve and the outflow control valve to be opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the second-stage refrigeration unit form a new refrigerant circulation channel. By switching the through-section valve, the inflow control valve and the outflow control valve by the refrigerant shunt controller, the temperature of the refrigerant introduced into the circulation channel of the lowest-stage refrigeration unit can be changed, the temperature span of the hot surface of the refrigeration component is changed, and the cooling structure of the refrigeration component can adjust the temperature range of the inner cavity of the sample box to a larger range, thereby improving the experimental effect and the application range of the experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly describes the drawings required for use in the description of the embodiments. Obviously, the drawings described are only part of the embodiments of the present invention, not all of the embodiments, and those skilled in the art can also obtain other design solutions and drawings based on these drawings without creative work.

[0022] Figure 1 It is a structural diagram of an ultra-low temperature open frost heave experimental system provided by an embodiment of the present invention, including a bracket, a sample box and a clamping device;

[0023] Figure 2 is a front perspective view of a sample box provided by an embodiment of the present invention;

[0024] Figure 3 is a top perspective view of a sample box provided by an embodiment of the present invention;

[0025] Figure 4 is a top view of an ultra-low temperature open frost heave experimental system provided by an embodiment of the present invention;

[0026] Figure 5 is a structural diagram of a frost heave measurement device provided by an embodiment of the present invention;

[0027] Figure 6 is a structural diagram of a bottom plate and a water adding device provided in one embodiment of the present invention;

[0028] Figure 7 is a structural diagram of a positioning member provided by an embodiment of the present invention;

[0029] Figure 8 It is a partial logic diagram of a low-temperature open frost heave experimental method provided by an embodiment of the present invention.

[0030] In the accompanying drawings: 110- bracket, 120- sample box, 121- left cover, 122- right cover, 130- top cover, 140- clamping device, 141- adjusting rod, 142- pressing end, 210- refrigeration component, 220- bottom plate, 230- insulation plate, 231- receiving groove, 240- pressing plate, 410- connecting plate, 511- indicator plate, 512- measuring rod, 513- sleeve, 520- adjusting through hole, 530- positioning screw, 610- penetration through hole, 620- measuring cylinder, 630- water pipe, 710- positioning component, 720- refrigeration element, 730- cold runner, 740- hot runner, 750- extension runner. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. In addition, all the connection relationships mentioned in the text do not refer to the direct connection of components, but refer to the formation of a better connection structure by adding or reducing connecting accessories according to the specific implementation situation. The various technical features in the present invention can be combined interchangeably without conflicting with each other.

[0032] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0033] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0034] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0035] Reference Figure 1 , Figure 2 and Figure 3 The ultra-low temperature open frost heave experimental system includes a refrigeration device, which includes a refrigeration component 210; a sample box 120, a top cover 130 is provided at the top opening of the sample box 120, the bottom of the inner cavity of the sample box 120 is covered with a bottom plate 220, and the end surface of the bottom plate 220 is provided with a plurality of penetration holes 610, the bottom plate 220 can slide along the inner wall of the sample box 120, the refrigeration component 210 is arranged on the top cover 130, and the cooling structure of the refrigeration component 210 is directly opposite to the inner cavity of the sample box 120; a clamping device 140, which has a clamping end 142 that can be adjusted up and down, and the clamping end 142 can press the top cover 130 and the sample box 120 against each other; a frost heave measuring device, which is fixed to the sample box 120, and the frost heave measuring device is provided with a retractable measuring end, which extends upward and always abuts against the bottom plate 220.

[0036] Specifically, unlike the natural temperature in ordinary cold regions, the ultra-low temperature environment will affect the water migration process of rock and soil. The water will freeze and cause the volume of rock and soil to expand. Therefore, the problem of rock and soil frost heave rate needs to be reconsidered. In addition, the sudden change of rock and soil frost heave will also lead to different time for disaster relief. During the experiment, the refrigeration device provides an ultra-low temperature experimental environment for the sample box 120. The water absorbed by the rock and soil body is easy to freeze directly, causing the volume of the entire rock and soil body to expand. The experimenter clamps the top cover 130 and the sample box 120 in advance through the pressing end 142 to prevent the rock and soil body sample from freezing the sample box 120. The top cover 130 is lifted up to reduce the gap between the sample box 120 and the top cover 130, ensuring that the experiment can be carried out smoothly in an ultra-low temperature environment. In addition, when the sample expands, it will squeeze the bottom plate 220. The top cover 130 and the sample box 120 are pressed against each other, limiting the sample to expand downward, so that the bottom plate 220 slides downward along the inner wall of the sample box 120. At this time, the frost heave measuring device and the sample box 120 are relatively fixed, and the displacement of the bottom plate 220 drives the displacement of the measuring end. The frost heave strain of the rock and soil body can be obtained by detecting the position change of the measuring end, which provides convenience for analyzing different freezing rates of the samples.

[0037] The measuring end of the frost heave measuring device can support the bottom plate 220 to prevent the bottom plate 220 from falling directly downward. The refrigeration element 210 is arranged on the top cover 130, and the cooling structure of the refrigeration element 210 is directly opposite to the inner cavity of the sample box 120, so as to directly refrigerate the inner cavity of the sample box 120. The top cover 130 blocks the opening of the sample box 120, which can reduce the evaporation of water in the rock and soil body during the experiment, and at the same time, it plays a role in keeping the inner cavity of the sample box 120 cold, thereby ensuring the refrigeration effect of the refrigeration element 210. It should be noted that the shape of the bottom plate 220 and the inner cavity of the sample box 120 match each other. In fact, the bottom plate 220 can be directly stuck in the inner cavity of the sample box 120, and the bottom plate 220 can be directly squeezed downward by the expansion of the rock and soil sample, or the bottom plate 220 can be connected to the sample box 120 through a slide block, etc., to improve the sliding effect.

[0038] Furthermore, in order to reduce the interference that may occur during the adjustment of the clamping device 140, the present invention further includes a bracket 110, the sample box 120 is placed on the bracket 110, the clamping device 140 is arranged on the bracket 110, and the pressing end 142 is located above the top cover 130, and the pressing end 142 can move downward and press on the top cover 130. To prevent the movement of the sample box 120 from affecting the position of the bottom plate 220 and the water adding device, in addition, without considering the interference, the clamping device 140 can also have two pressing ends 142, and the two pressing ends 142 can be separated from each other or close to each other, so that the sample box 120 and the top cover 130 are clamped to each other to improve the sealing effect. In addition, the top cover 130 can also be fixedly arranged on the bracket 110, and the pressing end 142 supports the sample box 120, so that the sample box 120 can move upward and press on the top cover 130. The clamping device 140 can be a clamping claw cylinder or a common cylinder, or an automatically driven device such as a motor, or a structure that adopts manual adjustment, such as thread adjustment, etc.

[0039] In addition, the clamping device 140 includes an adjustment rod 141, which is arranged in the up-down direction. The upper end of the adjustment rod 141 is threadedly connected to the bracket 110, and the lower end of the adjustment rod 141 is a clamping end 142. At least two adjustment rods 141 are arranged circumferentially around the center line of the sample box 120. The adjustment rod 141 is threadedly connected to the bracket 110, and the structure is stable and the cost is low. It should be noted that the adjustment rod 141 can move up and down along the bracket 110. In fact, in addition to being threadedly connected to the bracket 110, the adjustment rod 141 can also be driven by a cylinder, a motor screw, etc.

[0040] Furthermore, in the present embodiment, the top cover 130 includes a pressing plate 240 and an insulation plate 230 which are arranged from top to bottom. The bottom surface of the insulation plate 230 is provided with a receiving groove 231, and the refrigeration component 210 is arranged on the receiving groove 231. The insulation plate 230 further improves the cooling effect of the top cover 130. The pressing plate 240 can be a hard plate made of acrylic or other materials. The pressing end 142 is directly pressed on the pressing plate 240 to prevent the pressing end 142 from directly pressing the insulation material and reduce the possibility of damage. At the same time, there can be four adjusting rods 141 which are arranged at the four corners of the pressing plate 240 to improve the uniform force and the compression stability and reduce the possibility of the entire top cover 130 being lifted up at a corner when the rock and soil expand. Further, referring to Figure 4, with two adjustment rods 141 as a pressing group, a connecting plate 410 is connected between the two adjustment rods 141 in the same group, and four pressing groups are arranged at the four corners of the pressing plate 240, and a triangular area is formed between the connecting plate 410 and the corners, so as to increase the pressure area, ensure uniform force, reduce the eccentricity of the top cover 130, and improve the pressing stability. It should be noted that there can actually be only two, three, five, six or even more adjustment rods 141, as long as the multiple adjustment rods 141 are arranged circumferentially around the center of the vertical direction of the sample box 120.

[0041] Moreover, refer to Figure 5 The frost heave measuring device includes at least two dial indicators, which are arranged circumferentially around the center line of the bottom plate 220. The dial indicators include an indicator plate 511 and a measuring rod 512. The indicator plate 511 and the sample box 120 are relatively fixed. The measuring rod 512 is telescopically connected to the indicator plate 511, and the end of the measuring end abutting the bottom plate 220 is the end of the measuring rod 512 away from the indicator plate 511. The two dial indicators are arranged circumferentially around the center line of the bottom plate 220, which provides a more stable support effect for the bottom plate 220. In addition, because the frost heave process of the rock and soil body is uncontrollable, it is easy to cause the bottom plate 220 to tilt. The two dial indicators respectively detect the movement of the two sides of the bottom plate 220 and record the tilt state of the bottom plate 220. The freezing rate of the sample can be calculated more accurately, and the experimental accuracy can be improved. In fact, the dial indicator is in an inverted state during the experiment, and the dial indicator can also have three, four or more.

[0042] Furthermore, the dial indicator also includes a sleeve 513, the sleeve 513 and the indicator dial 511 are relatively fixed, the measuring rod 512 can slide along the inner wall of the sleeve 513, the bracket 110 is provided with an adjustment hole 520, the sleeve 513 can slide along the adjustment hole 520, and the bracket 110 is threadedly connected with a positioning screw 530, which extends into the adjustment hole 520 and presses against the outer wall of the sleeve 513. The indicating plate 511 and the sleeve 513 are relatively fixed to the sample box 120. The sleeve 513 is sleeved on the measuring rod 512 to increase the activity stability of the measuring rod 512. In addition, the sleeve 513 of the dial indicator is partially adjustable on the bracket 110. The experimenter can adjust the upper and lower positions of the sleeve 513 in the adjusting through hole 520, and then lock and position the sleeve 513 by the positioning screw 530. The structure is reliable, and the position of the dial indicator can be adjusted according to the position of the bottom plate 220. At the same time, there is no need to block the indicating plate 511. The experimenter can directly observe the data of the indicating plate 511, which is convenient and fast. The overall position of the dial indicator can be adjusted by adjusting the position of the sleeve 513 in the adjusting through hole 520, and the dial indicator can also be separated from the frame to improve the installation flexibility.

[0043] In addition, refer to Figure 6 The present invention also includes a water adding device, which includes a measuring cylinder 620 and a water pipe 630. The measuring cylinder 620 is arranged on the bracket 110. One end of the water pipe 630 is connected to the bottom opening of the measuring cylinder 620. The other end of the water pipe 630 is connected to the plurality of penetration holes 610 and connected to the bottom surface of the bottom plate 220. The water pipe 630 and the measuring cylinder 620 are connected to form a communicating vessel to realize automatic water replenishment of the bottom plate 220, which satisfies γ*h=F, wherein γ is the gravity of water, h is the height of the measuring cylinder 620 higher than the top surface of the bottom plate 220, and F is the pore water pressure in the bottom plate 220. By adjusting the liquid level in the measuring cylinder 620, a continuous and stable water source is controlled on the top surface of the bottom plate 220. At the same time, the amount and rate of water migration can be read on the measuring cylinder 620, which is convenient for the experimenter to record and improve the experimental effect. Furthermore, the permeable through holes 610 may be connected one by one with the water pipes 630, or the water pipes 630 may directly cover a plurality of permeable through holes 610 to achieve communication.

[0044] Furthermore, because a gap is likely to appear between the side of the bottom plate 220 and the inner cavity of the sample box 120 during the installation process or during the freezing and thawing process, in some embodiments, a sealing bag is provided at the bottom of the sample box 120, and the water pipe 630 passes through the sealing bag downward, and the sealing bag is covered at the bottom of the sample box 120, so that during the experiment, the influence of the gap between the bottom plate 220 and the sample box 120 on the experimental results is reduced, and the experimental accuracy is improved. In fact, a positioning platform is provided at the bottom of the outer periphery of the sample box 120, and the sealing bag is covered on the positioning platform, which facilitates the installation of the sealing bag. Moreover, the bottom plate 220 is actually a permeable stone with multiple penetration holes 610 to improve the water penetration effect. In actual use, the permeable stone is connected with one end of the water pipe 630 with neutral ketone glass glue to form a fixed nozzle, and the measuring cylinder 620 is fixed to the fixing clip on the external structure. In addition, two or more dial indicators are circumferentially and fixedly arranged at the bottom of the permeable stone. The water pipe 630 is led out from the middle of the bottom surface of the permeable stone. After the sealing bag is put on the bottom of the sample box 120, the indicator disk 511 of the dial indicator and the water pipe 630 are both downwardly passed through the sealing bag, which is convenient for the experimenter to check the data of the indicator disk 511 and avoid the water pipe 630. The sealing bag prevents the loss of water at the bottom of the sample and the evaporation of water, thereby reducing interference with the experiment.

[0045] At the same time, the sample box 120 is connected to the top cover 130 by magnetism, and the sample box 120 includes a left cover 121 and a right cover 122, one end of the left cover 121 and one end of the right cover 122 are hinged to each other, the other end of the left cover 121 and the other end of the right cover 122 are connected by magnetism, the left cover 121 and the right cover 122 are covered with each other to form a box body, and the clamping device 140 also includes a shielding member, which is sleeved on the outer wall of the box body. When it is necessary to replace the rock and soil sample, the experimenter directly opens the top cover 130, and then breaks open the end of the magnetic connection between the left cover 121 and the right cover 122. The left cover 121 and the right cover 122 can rotate relative to each other to fully open the inner cavity of the box body. During the opening process, because the bottom plate 220 is supported by the measuring end of the frost heave measuring device, the positions of the bottom plate 220 and the bracket 110 remain relatively fixed. The experimenter can directly take out the sample placed on the bottom plate 220 without completely disassembling the sample box 120 or removing the bottom plate of the water adding device. The sample can be replaced by disassembling the plate 220 and the water pipe 630, or even disassembling the frost heave measuring device, which reduces the process of reinstallation and wiring, facilitates the direct replacement of samples, and improves the experimental efficiency. In addition, during the experiment, the enclosure can prevent the frost heave of the rock and soil body from stretching the left cover 121 and the right cover 122 apart, thereby improving the experimental stability. In fact, the enclosure can be a tape, and the enclosure can be set at the joint between the top cover 130 and the sample box 120, which can further improve the sealing effect between the top cover 130 and the sample box 120. In addition, a partition layer that can reduce friction is provided on the inner wall of the sample box 120, and the partition layer can be kraft paper to reduce the friction between the sample and the side wall.

[0046] Moreover, in order to achieve an ultra-low temperature effect in the experimental environment, in some embodiments, the refrigeration device includes at least two-stage refrigeration units, the refrigeration unit includes a circulation channel and a refrigeration element 720, the circulation channel includes a cooling section and a heat transfer section, the hot surface of the refrigeration element 720 faces the heat transfer section of the same refrigeration unit, and the cold surface of the refrigeration element 720 faces the cooling section of the next-stage refrigeration unit. The refrigeration element 210 is the refrigeration element 720 of the lowest-stage refrigeration unit, and the cooling structure of the refrigeration element 210 is the cold surface of the refrigeration element 210. Specifically, the refrigerant in the cooling section of the upper refrigeration unit is cooled by an external condensing box, and the refrigerated refrigerant continuously flows along the circulation channel, and cools the hot surface of the refrigeration element 720, so that the cold surface of the refrigeration element 720 is further cooled, and acts on the refrigerant in the cooling section of the next refrigeration unit to achieve secondary refrigeration. The refrigerant after secondary refrigeration exchanges heat with the hot surface of the second unit refrigeration element 720 along the circulation channel, so that the cold surface of the second unit refrigeration element 720, that is, the refrigeration element 210, can cool the inner cavity of the sample box 120, and the three-stage refrigeration is realized as a whole, and the sample in the sample box 120 is ultra-low temperature frozen, which is convenient for building a rock and soil ultra-low temperature, variable freezing rate type open frost heave simulation and observation test system. In fact, the refrigeration element 720 can be a semiconductor refrigeration sheet.

[0047] And, refer to Figure 7The refrigeration unit also includes a positioning member 710, which has a cooling channel inside. The refrigeration element 720 is arranged along the extension direction of the cooling channel and divides the cooling channel into a cold runner 730 and a hot runner 740. The adjacent two-stage refrigeration units are respectively a first unit and a second unit. The heat transfer section of the first unit is located in the hot runner 740, and the cooling section of the second unit is located in the cold runner 730. Both ends of the hot runner 740 and both ends of the cold runner 730 are connected with an extension channel 750, which extends to the surface of the positioning member 710. The two extension channels 750 at the same side end of the cooling channel extend in a direction away from each other. The hot runner 740 and the extension channels 750 at both ends thereof, as well as the cold runner 730 and the extension channels 750 at both ends thereof, belong to two different circulation channels, and the two circulation channels exchange heat through the hot runner 740 and the cold runner 730 that merge with each other. Moreover, the positioning member 710 is actually X-shaped, and the pipelines extending around the positioning member 710 form an extension channel 750. Both ends of the cooling channel are connected with the extension channel 750. The extension channels 750 on the same side gradually approach each other in the direction close to the cooling channel. The extension channels 750 are spaced apart to reduce the spread of heat. At the same time, the pipelines of the positioning member 710 are made of high-density extruded polystyrene foam plastics to improve the heat preservation effect of the pipeline. In addition, the cooling element 720 located in the cooling channel includes a plurality of cooling plates, that is, a plurality of semiconductor cooling plates, which are arranged in sequence along the cooling channel and bonded to each other to improve the cooling length and cooling effect.

[0048] In addition, a temperature sensor can be provided on the cold surface of the refrigeration component 210, and a humidity sensor can be provided in the inner cavity of the sample box 120. Moreover, temperature sensors can also be installed on the cold and hot surfaces of the refrigeration element 720. The circuits on the external intelligent adjustment system are connected to the refrigeration component 210, temperature sensors, humidity sensors, and relays through line pipes to improve the control accuracy of sample humidity and temperature.

[0049] Furthermore, because conventional tests often use a compressor to cool the inner cavity of the sample box 120, the cooling effect of the compressor is limited, and in order to reach the experimental temperature, it is often necessary to wait for 3-5 hours, which takes a long time to prepare and is uncontrollable, which is not conducive to the simulation of the test environment. The present invention also provides a low-temperature open frost heave test method, including the above-mentioned ultra-low temperature open frost heave test system, including the following steps: S1, loading and taking samples into the sample box 120, adjusting the pressing end 142 of the clamping device 140, and making the pressing end 142 press the top cover 130 on the sample box 120, the frost heave measuring device is relatively fixed to the sample box 120, and the retractable measuring end is pressed against the bottom surface of the bottom plate 220; S2, the refrigeration device includes a refrigeration unit, and the refrigeration units are respectively a room temperature refrigerant refrigeration unit, a first-level refrigeration unit, a second-level refrigeration unit and a third-level refrigeration unit at the lowest level, the refrigeration unit includes a circulation channel, a refrigeration element 720, a temperature sensor and a temperature adjustment module, the circulation channel includes a cooling section and a heat transfer section, in any two adjacent refrigeration units, the hot surface of the refrigeration element 720 of the refrigeration unit at the upper level faces the heat transfer section at the same level, and the cold surface of the refrigeration element 720 faces the cooling section of the refrigeration unit at the lower level, and the lower level of the refrigeration unit The refrigeration element 720 is the refrigeration part 210, and the refrigeration part 210 is arranged on the top cover 130, and the cold surface of the refrigeration part 210 faces the inner cavity of the sample box 120. The temperature sensor can detect the temperature of the cooling section and the heat transfer section. The temperature adjustment module is connected to the refrigeration element 720, and the temperature sensor and temperature adjustment module of each level of refrigeration unit are connected to the control module; S3, the water replenishment device replenishes water for the sample in the inner cavity of the sample box 120; S4, the control module converts the received expected value into a first control signal, and then sends the first control signal to the temperature adjustment modules of the refrigeration units at each level. After receiving the first control signal, the temperature adjustment module adjusts the refrigeration temperature and refrigeration rate of the refrigeration element 720 at the same level. The control module receives the measured value periodically detected by the temperature sensor. The control module compares the measured value with the expected value through the temperature control program and converts it into a second control signal. The second control signal is used to drive the temperature adjustment module to adjust the refrigeration temperature and refrigeration rate of the refrigeration element 720 at the same level.

[0050] The present invention can control the temperature and cooling rate of the ultra-low temperature environment in the inner cavity of the sample box 120, provide an ultra-low temperature test environment for the sample, and refer to Figure 8, the circulation channel of each refrigeration unit is provided with an on-off valve, and the circulation channel of the lowest refrigeration unit is provided with an inflow control valve and an outflow control valve. Except for the circulation channels of the lowest refrigeration units, all are connected to the inflow control valve and the outflow control valve. The inflow control valve, the outflow control valve and the plurality of through-section valves are connected to the refrigerant shunt controller. The refrigerant shunt controller is connected to the control module. After receiving the expected value, the control module sends a switching signal to the refrigerant shunt controller, so that the corresponding through-section valve, the inflow control valve and the outflow control valve are opened or closed, so that the circulation channel of the lowest refrigeration unit can be switched and connected to the circulation channel of any upper refrigeration unit. If you want to connect the circulation channel of a certain level of refrigeration unit to the refrigeration channel of the lowest level, you only need to open the corresponding outflow control valve and inflow control valve of the level, and close the interfaces of the corresponding outflow control valve and inflow control valve of the refrigeration units of other levels. The cooling structure of the refrigeration unit 210 can adjust the temperature range of the inner cavity of the sample box 120 to improve the experimental effect and the application range of the experiment.

[0051] Furthermore, the refrigeration units include a room temperature refrigerant refrigeration unit, a first-stage refrigeration unit, a second-stage refrigeration unit and a third-stage refrigeration unit at the lowest level. When the control module receives the expected value, the following conditions are met: the expected value is within the threshold range of 0°C to -20°C, the refrigerant shunt controller receives the switching signal and controls the on-off valves of the room temperature refrigerant refrigeration unit and the third-stage refrigeration unit to be disconnected, the inlet control valve and the outlet control valve to be opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the room temperature refrigerant refrigeration unit to form a new refrigerant circulation channel; the expected value is within the threshold range of -20°C to -40°C, the refrigerant shunt controller receives the switching signal and controls the on-off valves of the room temperature refrigerant refrigeration unit and the third-stage refrigeration unit to be disconnected, the inlet control valve and the outlet control valve to be opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the room temperature refrigerant refrigeration unit to form a new refrigerant circulation channel. The controller receives the switching signal and controls the on-off valves of the first-stage refrigeration unit and the third-stage refrigeration unit to be disconnected, the inlet control valve and the outflow control valve to be opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the first-stage refrigeration unit form a new refrigerant circulation channel; the expected value is within the threshold range of -40℃ to -70℃, the refrigerant branch controller receives the switching signal and controls the on-off valves of the second-stage refrigeration unit and the third-stage refrigeration unit to be disconnected, the inlet control valve and the outflow control valve to be opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the second-stage refrigeration unit form a new refrigerant circulation channel. The control module of the present invention is an Arduino control chip, which is connected to an external computer. The computer has a temperature control program. The user inputs an expected value into the computer, so that the temperature control program determines and sends a first control signal, that is, a voltage adjustment signal, to the temperature adjustment module, which is actually a numerical control step-down module. The refrigeration element of the room temperature refrigerant refrigeration unit includes a heat dissipation fan and a heat dissipation metal. The air outlet direction of the heat dissipation fan faces the heat dissipation metal. The heat dissipation metal is arranged at the temperature reduction section of the room temperature refrigerant refrigeration unit. The first-stage refrigeration unit also includes a condensation box, a compressor and an evaporation plate. The condensation box is provided with a condensation channel. The refrigeration element 720 of the first-stage refrigeration unit is a compressor. The compressor The evaporator plate is used for refrigeration, the evaporator plate forms a cold surface, and the condensation channel is laid on the evaporator plate to achieve cooling. The part of the circulation channel passing through the condensation channel is the cooling section. The refrigeration elements 720 of the second-stage refrigeration unit and the third-stage refrigeration unit are semiconductor refrigeration sheets. The semiconductor refrigeration sheets are connected to the CNC step-down module. The refrigeration temperature and refrigeration speed of the semiconductor refrigeration sheets are adjusted by the voltage adjustment signal to control the time required for refrigeration. The user can detect the frost heave process and results of the sample under different variable freezing rate types or any low temperature environment between 0℃ and -70℃, and accurately construct the frost heave model in cold area engineering, which is of great significance for the study of moisture migration under rapid ultra-low temperature cooling conditions.

[0052] The preferred embodiments of the present invention are specifically described above, but the present invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. An ultra-low temperature open frost heave experimental system, characterized in that: include: A refrigeration device, comprising a refrigeration element (210); A sample box (120) is provided with a top cover (130) at its top opening, the bottom of the inner cavity of the sample box (120) is covered with a bottom plate (220), the bottom plate (220) is capable of sliding up and down along the inner wall of the sample box (120), the refrigeration element (210) is arranged on the top cover (130), and the cooling structure of the refrigeration element (210) is directly opposite to the inner cavity of the sample box (120); A clamping device (140) having a clamping end (142) that can be adjusted up and down, wherein the clamping end (142) can press the top cover (130) and the sample box (120) against each other; a frost heave measurement device, which is fixed to the sample box (120), the frost heave measurement device being provided with a retractable measurement end, the measurement end extending upward and always abutting against the bottom plate (220); The refrigeration device comprises at least two stages of refrigeration units, wherein the refrigeration units comprise a circulation channel, a refrigeration element (720), a temperature sensor and a temperature adjustment module; the circulation channel comprises a cooling section and a heat transfer section; in any two adjacent refrigeration units, the hot surface of the refrigeration element (720) located in the upper stage refrigeration unit faces the heat transfer section at the same stage, and the cold surface of the refrigeration element (720) faces the cooling section of the refrigeration unit at the lower stage; the refrigeration element (210) is the refrigeration element (720) of the lowermost stage refrigeration unit; the cooling structure of the refrigeration element (210) is the cold surface of the refrigeration element (210); the temperature sensor can detect the temperature of the cooling section and the heat transfer section; the temperature adjustment module is connected to the refrigeration element (720); each The temperature sensors and temperature adjustment modules of the first-level refrigeration units are connected to the control module, the circulation channels of each level of refrigeration units are provided with on-off valves, the circulation channels of the lowest-level refrigeration units are provided with inflow control valves and outflow control valves, the circulation channels of the refrigeration units other than the lowest-level refrigeration units are connected to the inflow control valves and outflow control valves, the inflow control valves, the outflow control valves and the on-off valves are all connected to the refrigerant shunt controller, the refrigerant shunt controller is connected to the control module, after receiving the expected value, the control module sends a switching signal to the refrigerant shunt controller, so that the corresponding on-off valves, inflow control valves and outflow control valves are opened or closed, so that the circulation channel of the lowest-level refrigeration unit can be switched and connected to the circulation channel of any upper-level refrigeration unit; The at least two-stage refrigeration unit includes a room temperature refrigerant refrigeration unit, a first-stage refrigeration unit, a second-stage refrigeration unit, and a third-stage refrigeration unit at the lowest level. When the control module receives the expected value, the following conditions are met: When the expected value is within the threshold range of 0°C to -20°C, the refrigerant shunt controller receives the switching signal and controls the on / off valves of the room temperature refrigerant refrigeration unit and the third-stage refrigeration unit to be disconnected, the inflow control valve and the outflow control valve to be opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the room temperature refrigerant refrigeration unit form a new refrigerant circulation channel; When the expected value is within the threshold range of -20℃ to -40℃, the refrigerant shunt controller receives the switching signal and controls the on / off valves of the first-stage refrigeration unit and the third-stage refrigeration unit to be disconnected, the inflow control valve and the outflow control valve to be opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the first-stage refrigeration unit form a new refrigerant circulation channel; The expected value is within the threshold range of -40℃ to -70℃. The refrigerant branch controller receives the switching signal and controls the on-off valves of the second-stage refrigeration unit and the third-stage refrigeration unit to be disconnected, the inlet control valve and the outflow control valve are opened, and the circulation channel of the third-stage refrigeration unit and the circulation channel of the second-stage refrigeration unit form a new refrigerant circulation channel.

2. The ultra-low temperature open frost heave experimental system according to claim 1, characterized in that: It also includes a bracket (110), the sample box (120) is placed on the bracket (110), the clamping device (140) is arranged on the bracket (110), the pressing end (142) is located above the top cover (130), and the pressing end (142) can move downward and press on the top cover (130).

3. The ultra-low temperature open frost heave experimental system according to claim 2, characterized in that: The clamping device (140) comprises an adjusting rod (141), the adjusting rod (141) being arranged in the up-down direction, the upper end of the adjusting rod (141) being threadedly connected to the bracket (110), the lower end of the adjusting rod (141) being the pressing end (142), and at least two adjusting rods (141) being arranged circumferentially around the center line of the sample box (120); The frost heave measurement device comprises at least two dial indicators, which are arranged circumferentially around the center line of the base plate (220), and the dial indicator comprises an indicator disk (511) and a measuring rod (512). The indicator disk (511) and the sample box (120) are relatively fixed, and the measuring rod (512) is telescopically connected to the indicator disk (511), and the measuring end is the measuring rod (512).

4. The ultra-low temperature open frost heave experimental system according to claim 2, characterized in that: The device also comprises a water adding device, the water adding device comprising a measuring cylinder (620) and a water pipe (630), the measuring cylinder (620) being arranged on the bracket (110), one end of the water pipe (630) being connected to the bottom opening of the measuring cylinder (620), the end surface of the bottom plate (220) being provided with a permeable through hole (610), the other end of the water pipe (630) being connected to the permeable through hole (610) and connected to the bottom surface of the bottom plate (220).

5. The ultra-low temperature open frost heave experimental system according to claim 1, characterized in that: The sample box (120) comprises a left cover member (121) and a right cover member (122), one end of the left cover member (121) and one end of the right cover member (122) are hinged to each other, the other end of the left cover member (121) and the other end of the right cover member (122) are magnetically connected, the left cover member (121) and the right cover member (122) are covered with each other to form a box body, the top cover (130) is magnetically connected to the top of the box body and covers the top opening of the box body, and the clamping device (140) further comprises a shielding member, which is sleeved on the outer wall of the box body.

6. A low-temperature open frost heave test method, using the ultra-low-temperature open frost heave test system as described in any one of claims 1 to 5, characterized in that: The following steps are involved: S1, loading a sample into a sample box (120), adjusting the pressing end (142) of the clamping device (140) so that the pressing end (142) presses the top cover (130) onto the sample box (120), fixing the frost heave measurement device relative to the sample box (120), and placing the retractable measurement end against the bottom surface of the bottom plate (220); S2. The refrigeration device comprises at least two stages of refrigeration units, wherein the refrigeration units comprise a circulation channel, a refrigeration element (720), a temperature sensor and a temperature adjustment module. The circulation channel comprises a cooling section and a heat transfer section. In any two adjacent stages of the refrigeration units, the hot surface of the refrigeration element (720) of the refrigeration unit at the upper stage faces the heat transfer section at the same stage, and the cold surface of the refrigeration element (720) faces the cooling section of the refrigeration unit at the lower stage. The refrigeration element (720) of the refrigeration unit at the lower stage is the refrigeration element (210). The refrigeration element (210) is arranged on the top cover (130), and the cold surface of the refrigeration element (210) faces the inner cavity of the sample box (120). The temperature sensor can detect the temperature of the cooling section and the heat transfer section. The temperature adjustment module is connected to the refrigeration element (720). The temperature sensor and the temperature adjustment module of each stage of the refrigeration unit are connected to the control module. S3, a water replenishing device replenishes water for the sample in the inner cavity of the sample box (120); S4, the control module converts the received expected value into a first control signal, and then sends the first control signal to the temperature adjustment modules of the refrigeration units at each level. After receiving the first control signal, the temperature adjustment module adjusts the refrigeration temperature and refrigeration rate of the refrigeration element (720) at the same level. The control module receives the actual value detected periodically by the temperature sensor, compares the actual value with the expected value and converts it into a second control signal. The second control signal is used to drive the temperature adjustment module to adjust the refrigeration temperature and refrigeration rate of the refrigeration element (720) at the same level.

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