A test device and method for verifying the similarity law of high gravity earth-air convection heat transfer

Abstract

The present invention discloses a similarity law verification test device and method for supergravity earth-air convective heat transfer. The input end of the airflow feedback control system is connected to an air supply system composed of an air compressor, a dryer and a precooler, and the output end is connected to a vortex tube refrigeration system; the compressed air is separated by a vortex in the vortex tube to form a cold airflow, which is passed into a soil sample cabin containing a vacuum insulation layer through a cold transmission pipeline, and the airflow passes over the soil surface to form a convective heat exchange boundary layer; by implementing feedback control on the compressed air pressure and flow rate, the cold flow state of the sample cabin is adjusted to achieve the simulation of the real atmosphere-soil interface convective heat transfer process, and the method includes device installation, soil-air interface convective heat transfer process realization, normal gravity / supergravity model test, and similarity law comparison verification based on temperature field. The present invention expands the application of supergravity physical simulation test technology in geotechnical engineering in cold regions, and is expected to provide technical support for the quantitative study of frozen soil melting problems in cold regions under the background of global warming.

Description

Technical Field

[0001] The invention relates to a similarity law verification simulation device and method in the field of geotechnical engineering, and in particular to a similarity law verification test device and method for supergravity earth-air convection heat transfer. Background Art

[0002] The ultra-gravity centrifuge simulation test has the characteristics of time reduction and scale reduction, and has outstanding advantages in solving "large-scale" and "long-duration" rock and soil disaster problems. It is now gradually applied to related research on frozen soil problems in cold regions. For example, some scholars have used ultra-gravity centrifuge tests to explore the mechanism of instability and collapse of frozen soil slopes under the action of long-term freeze-thaw cycles. In the design of ultra-gravity centrifuge simulation tests, in order to better restore the disaster process of the prototype rock and soil body, it is necessary to first ensure that the key physical processes of the disaster between the prototype and the model are similar, and secondly, it is necessary to ensure that the selection of the similarity scale of key physical quantities follows the real physical process.

[0003] At present, high-gravity tests on frozen soil have been carried out. The implementation methods of freeze-thaw physical process are mainly the following three modes: (1) The cooling process is realized by vortex tube refrigeration elements, and the heating process is realized by covering the soil surface with heating elements; (2) The cooling process is realized by covering the soil surface with ice blankets, and the heating process is realized directly by using the room temperature of the centrifuge room; (3) The heating / cooling is realized by semiconductors combined with air convection components. The similarity scale of related experiments adopts the soil heat transfer time similarity law proposed by Cambridge University, that is, the heat transfer time scale between the prototype and the model is N 2 .

[0004] The above-mentioned hypergravity test has two deficiencies in the experimental design. First, the model is not similar to the real physical process of the prototype. For example, in the two modes (1) and (2), the heat exchange of the soil is controlled by covering the temperature control element on the upper boundary of the soil, thereby realizing the simulation of frost heave-thaw settlement on the soil surface. The heat transfer process is heat conduction, which is not similar to the physical process of convective heat transfer between the actual soil and the atmosphere. Second, the heat transfer time similarity law is selected and does not match the physical process of the centrifuge model test. For example, although the mode (3) solves the problem of physical process dissimilarity, the test scale adopts the soil heat transfer time similarity law. The heat transfer mode in the soil is the heat conduction mode, which cannot effectively reflect the real thermal convection mode of the soil-air interface.

[0005] The convection mode and the conduction mode are significantly different in terms of heat transfer method and control equation. The simulation of the convection process is to see whether the prototype and the model follow the heat conduction N 2 The time scale is a fundamental problem that needs to be solved in the simulation of cold region engineering physics. In order to solve this scientific problem, it is urgent to propose an experimental method that can simulate the physical process of ground-air convection heat transfer, and develop a matching experimental device to scientifically and rigorously quantify the similarity law of ground-air convection heat transfer. Summary of the invention

[0006] In order to solve the problems existing in the background technology, the purpose of the present invention is to design a hypergravity earth-air convection heat transfer similarity law verification test device and method. The purpose of the present invention is to simulate the earth-air convection heat transfer process in the laboratory and finally determine the time similarity law under the hypergravity field.

[0007] The technical solution of the present invention is as follows:

[0008] 1. A test device for verifying the similarity law of high gravity earth-air convection heat transfer:

[0009] It includes an air supply system, an airflow feedback control system, a vortex tube refrigeration system and a sample cabin; the input end of the air supply system is connected to the outside atmosphere, the output end of the air supply system is connected to the input end of the airflow feedback control system through a pipeline, the output end of the airflow feedback control system is connected to the input end of the vortex tube refrigeration system through a pipeline, and the output end (i.e., the cold end) of the vortex tube refrigeration system is connected to the input end of the sample cabin.

[0010] The air source supply system is mainly composed of an air compressor, a dryer and a precooler; the input end of the air compressor is connected to the outside atmosphere, the output end of the air compressor is connected to the input end of the dryer through a pipeline, the output end of the dryer is connected to the input end of the precooler through a pipeline, the output end of the dryer is connected to the input end of the precooler through a pipeline, and the output end of the precooler is connected to the input end of the airflow feedback control system through a pipeline;

[0011] The airflow feedback control system is mainly composed of a pressure-type proportional valve, a flow-type proportional valve, a flow meter, a pressure gauge, and a programmable controller. One end of the pressure-type proportional valve is connected to the precooler as the input end of the airflow feedback control system, and the other end of the pressure-type proportional valve is connected to one end of the flow meter through a pipeline. A flow-type proportional valve is provided on the pipeline from the pressure-type proportional valve to the flow meter, and the other end of the flow meter is respectively connected to the pressure gauge and the input end of the vortex tube refrigeration system. The pressure-type proportional valve, flow-type proportional valve, flow meter and pressure gauge are all electrically connected to the programmable controller.

[0012] The vortex tube refrigeration system is mainly composed of a vortex tube component, a cooling pipeline and a vortex tube bracket; the vortex tube bracket is placed on the ground, the vortex tube component is placed on the vortex tube bracket, and the output end of the vortex tube component is connected to the input end of the sample cabin through the cooling pipeline.

[0013] The sample cabin is mainly composed of a cold flow cabin with a cavity inside, a soil sample container with a cavity inside and a steel support; the soil sample container is placed on the ground, the soil sample container is used to install the soil sample, the cold flow cabin is placed on the soil sample container and the cold flow cabin and the soil sample container are fixedly connected by the steel support, a plurality of exhaust holes and an air inlet are opened on the side wall of the cold flow cabin, the air inlet is connected to the cold delivery pipeline in the vortex tube refrigeration system as the input end of the sample cabin, the exhaust hole is connected to the outside atmosphere, the cold flow cabin is externally connected to a first temperature sensor, a plurality of sensor channels are arranged on the side wall of the soil sample container, an external second temperature sensor is buried in the soil sample in the soil sample container after passing through the sensor channel, a water delivery channel is arranged in the bottom plate of the soil sample container, and the water delivery channel is externally connected to an external water tank.

[0014] The side wall of the soil sample container includes a first side wall and a second side wall, the first side wall is located inside the second side wall and a sandwich layer is provided between the first side wall and the second side wall, the first side wall and the second side wall are provided with openings at the same position, the sensor channel passes through the openings of the second side wall and the first side wall in sequence and is connected with the cavity in the soil sample container, a vacuum hole is opened on the second side wall, and the vacuum layer is connected with an external vacuum pump through the vacuum hole.

[0015] The cold flow chamber and the soil sample container are both made of acrylic material.

[0016] The first temperature sensor and the second temperature sensor are both electrically connected to the programmable controller, and the first temperature sensor and the second temperature sensor are both thermocouple temperature sensors.

[0017] 2. A method for verifying the heat transfer similarity law of a device comprises the following steps:

[0018] Step 1, according to the preset soil sample size, a prototype sample and several model samples with different scale ratios are respectively made, the soil sample is a prototype sample or a model sample, the prototype sample is placed in a soil sample container, eleven second temperature sensors are arranged on the soil sample container, and then a cold flow cabin is installed on the soil sample container, and finally the side wall of the soil sample container is connected to a vacuum pump, and the vacuum pump is used to vacuum extract the sandwich layer in the soil sample container;

[0019] Step 2: After vacuum extraction is completed, an air compressor is used to generate a compressed air source, which is converted into a cold flow after passing through a dryer, a precooler, an airflow feedback control system and a vortex tube refrigeration system in sequence;

[0020] Step 3: Conduct a constant gravity simulation test

[0021] The cold flow generated in step 2 is passed into the cold flow chamber of the sample chamber containing the prototype sample through the cold delivery pipeline, and the temperature in the cold flow chamber is monitored by the pressure proportional valve, the flow proportional valve and the first temperature sensor. After reaching the preset temperature threshold, the temperature field of the prototype sample is obtained by the second temperature sensor;

[0022] Step 4: Conduct hypergravity simulation test

[0023] After the preset test time, the soil sample is taken out from the soil sample container, and a new model sample is placed in the soil sample container, the position of the second temperature sensor on the soil sample container is adjusted so that the second temperature sensor is placed at the preset position, the cold flow cabin is fixedly installed, and then the sandwich layer in the soil sample container is vacuum-extracted by a vacuum pump;

[0024] The sample compartment containing the model sample is placed in the hanging basket of the centrifuge, the gravity value of the centrifuge is controlled to reach a preset gravity value, the cold flow generated in step 2 is passed into the cold flow compartment of the sample compartment containing the model sample through the cold delivery pipeline, and the temperature in the cold flow compartment is monitored by a pressure proportional valve, a flow proportional valve and a first temperature sensor. After reaching a preset temperature threshold, the temperature field of the model sample is obtained by a second temperature sensor;

[0025] Step 5, repeat step 4 multiple times to obtain the temperature field of the model sample at different scale ratios;

[0026] Step 6. After the hypergravity simulation test and the normal gravity simulation test are completed, the temperature field of the model sample at each scale ratio is compared with the temperature field of the prototype sample to obtain the time similarity law of ground-air convection heat transfer of the model sample and the prototype sample, thereby realizing the analysis and calculation of the frozen soil moisture field and temperature field under real conditions.

[0027] The step 2 is specifically as follows: after completing the vacuum extraction, the air compressor is started to generate a compressed air source in the air compressor, and the generated compressed air source is sequentially input into the dryer and the pre-cooler through the pipeline to obtain a dry low-temperature air source, and then the dry low-temperature air source is introduced into the airflow feedback control system: the pressure and flow of the dry cold air source are adjusted in real time by using a pressure proportional valve and a flow proportional valve, and the pressure and flow of the dry cold air source are monitored in real time by using a pressure gauge and a flow meter. When the pressure and flow of the dry low-temperature air source reach the pressure value and flow value preset in the test respectively, the dry low-temperature air source is introduced into the vortex tube element, and the vortex tube element converts the dry low-temperature air source into a cold flow.

[0028] In the steps 3 and 4, after the temperature in the cold flow chamber is monitored by the pressure-type proportional valve, the flow-type proportional valve and the first temperature sensor to reach a preset temperature threshold, the temperature field of the soil sample is obtained by the second temperature sensor. The specific steps are: the temperature of the cold flow chamber is regulated by the pressure-type proportional valve and the flow-type proportional valve, and the temperature in the cold flow chamber is monitored in real time by the first temperature sensor. When the temperature of the cold flow chamber reaches the preset temperature threshold, the temperature of the soil sample at different depths is monitored and recorded in real time by the second temperature sensor to obtain the temperature field of the soil sample.

[0029] The gas source pressure at the input end of the vortex tube refrigeration system is controlled. Before the test starts, the pressure of the pressure-type proportional valve 4 is set to 0.7MPa through the PID programmable controller; after the test starts, the pressure gauge 7 monitors the gas source pressure value at the input end of the vortex tube refrigeration system in real time, and transmits the gas source pressure value model to the programmable controller; when the value of the pressure gauge 7 is the same as the initial set pressure value, the pressure-type proportional valve 4 maintains normal operation; when the pressure value of the pressure gauge 7 deviates from the initial set pressure value of the pipeline, the PID programmable controller sends a control model to the pressure-type proportional valve 4 to adjust the pipeline pressure to the same as the initial set pressure value; the entire control process ensures that the input end of the vortex tube refrigeration system is in a constant pressure state, avoiding the deviation of the results of the prototype and model tests due to changes in the gas source pressure during the test; the flow regulation process is the same as the pressure regulation process and will not be repeated.

[0030] The airflow feedback control system can ensure the stable operation of the prototype and model vortex tube refrigeration systems. In order to further reduce the test error, it is also necessary to ensure that the prototype and the model have the same heat transfer mode during the test. In the test, a constant cold airflow enters the sample cabin through the cold delivery pipe. The flow state of the airflow in the pipe can be divided into laminar flow and turbulent flow. The basis for judging whether it is in a laminar or turbulent state is the Reynolds number. When the Reynolds number Re≤2300, the fluid is in a laminar state in the pipe; when Re>2300, the fluid is in a turbulent state in the pipe; formula (1) is the Reynolds number calculation formula. In the test, when the cold airflow enters the sample cabin from the cold delivery pipe through the above formula (1), the cold airflow has the same Reynolds number in the prototype and the model, and the airflow is in the same flow state, so it has the same heat transfer mode.

[0031] Re=udv (1)

[0032] Where: u is the velocity of the cold air flow in the cold transport pipeline;

[0033] v—fluid kinematic viscosity, which can be found through the fluid mechanics table;

[0034] d—Inner diameter of the cooling pipe.

[0035] The present invention provides a theoretical and experimental basis for the application of hypergravity physical simulation test technology in geotechnical engineering in cold regions, and is expected to provide technical support for precise quantitative research on issues such as glacier melting and permafrost melting in cold regions under the background of global warming.

[0036] The input end of the airflow feedback control system is connected to the air supply system composed of an air compressor, a dryer and a precooler, and the output end is connected to the vortex tube refrigeration system; the compressed air is separated by the vortex of the vortex tube to form a cold airflow, which is passed into the sample cabin containing a vacuum insulation layer through a cold transmission pipeline; a vacuum interlayer is designed on the side wall of the sample cabin to avoid lateral thermal erosion of the sample in the sample cabin by the external temperature during long-term testing. A soil model is prepared in the cabin, and the airflow passes over the surface of the soil to form a convective heat exchange boundary layer; the compressed air pressure and flow rate at the input end of the vortex tube are adjusted by the airflow feedback control system, and the cold flow velocity at the output end is controlled to achieve flow control of the cold flow in the sample cabin, thereby reproducing the real atmosphere-soil interface convective heat exchange process. The present invention provides a theoretical and experimental basis for the application of hypergravity physical simulation test technology in geotechnical engineering in cold regions, and is expected to provide technical support for quantitative research on issues such as glacier melting and permafrost melting in cold regions under the background of global warming.

[0037] The beneficial effects of the present invention are:

[0038] 1. The present invention uses vortex tube elements to provide cooling for the temperature change inside the sample cabin, and simulates the real heat transfer process between the atmosphere and the surface under hypergravity, so that the hypergravity simulation test process is closer to the real environment on site;

[0039] 2. The present invention ensures that the airflow patterns on the soil surfaces of different test groups are similar by monitoring and feedback controlling the cold airflow at the entrance of the sample cabin. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the general design diagram of the device for verifying the similarity law of supergravity earth-air convection heat transfer;

[0041] Figure 2 This is a detailed diagram of the refrigeration system and sample chamber;

[0042] Figure 3 The sample cabin cross-section diagram is shown in the figure;

[0043] In the figure: 1. air compressor; 2. dryer; 3. precooler; 4. pressure proportional valve; 5. flow proportional valve; 6. flow meter; 7. pressure gauge; 8. programmable controller; 9. vortex tube refrigeration system; 901. vortex tube original; 902. cold transmission pipeline; 903. vortex tube bracket; 10. sample cabin; 1001. cold flow cabin; 1002. exhaust hole; 1003. soil sample container; 1004. sensor channel; 1005. steel support; 1006. bolt; 1007. flange connection structure; 1008. vacuum hole; 1009. vacuum insulation layer; 1010. water transmission channel. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0045] like Figure 1 As shown, the device includes an air supply system, an airflow feedback control system, a vortex tube refrigeration system 9 and a sample chamber 10; the input end of the air supply system is connected to the outside atmosphere, the output end of the air supply system is connected to the input end of the airflow feedback control system through a pipeline, the output end of the airflow feedback control system is connected to the input end of the vortex tube refrigeration system 9 through a pipeline, the output end (i.e., the cold end) of the vortex tube refrigeration system 9 is connected to the input end of the sample chamber 10, and the air supply system is used to provide the required high-pressure-dry-low-temperature air source for the simulation test; the airflow feedback control system is monitored and controlled by a PID programmable controller 8 The air flow pressure and flow rate at the input end of the vortex tube refrigeration system 9 ensure the constant pressure and constant flow of the pipeline gas source at the input end of the vortex tube refrigeration system 9; the high-pressure-dry-low-temperature gas source is introduced into the vortex tube refrigeration system 9 after constant pressure and constant flow control, and the required temperature cold flow is obtained from the vortex tube original component 901, and then introduced into the sample cabin 10 through the cold delivery pipeline 902; the sample cabin 10 is composed of an upper cold flow cabin 1001 and a lower soil sample cabin 1003. The vortex tube refrigeration system 9 generates a cold flow that enters the upper cold flow cabin 1001 and emits convective heat exchange with the soil in the lower soil sample cabin 1003, thereby simulating ground-air convective heat exchange.

[0046] The air source supply system is mainly composed of an air compressor 1, a dryer 2 and a precooler 3; the input end of the air compressor 1 is connected to the outside atmosphere, the output end of the air compressor 1 is connected to the input end of the dryer 2 through a pipeline, the output end of the dryer 2 is connected to the input end of the precooler 3 through a pipeline, the output end of the dryer 2 is connected to the input end of the precooler 3 through a pipeline, the output end of the dryer 2 is connected to the input end of the precooler 3 through a pipeline, and the output end of the precooler 3 is connected to the input end of the airflow feedback control system through a pipeline. The air compressor 1 is used to provide a compressed air source for normal operation of the vortex tube refrigeration system 9; the dryer 2 dehumidifies and dries the compressed air source generated by the air compressor 1 to make the high-pressure air source free of moisture, thereby preventing moisture in the air source from entering the vortex tube refrigeration system 9, thereby causing the internal corrosion performance of the vortex tube element 901 to decrease; the precooler 3 cools the dried high-pressure air source so that the high-pressure dry air source enters the vortex tube refrigeration system 9 at a lower temperature, thereby improving the refrigeration efficiency of the vortex tube element 901;

[0047] The airflow feedback control system is mainly composed of a pressure-type proportional valve 4, a flow-type proportional valve 5, a flow meter 6, a pressure gauge 7, and a programmable controller 8. One end of the pressure-type proportional valve 4 is connected to the precooler 3 as the input end of the airflow feedback control system, and the other end of the pressure-type proportional valve 4 is connected to one end of the flow meter 6 through a pipeline. A flow-type proportional valve 5 is provided on the pipeline from the pressure-type proportional valve 4 to the flow meter 6. The other end of the flow meter 6 is respectively connected to the pressure gauge 7 and the input end of the vortex tube refrigeration system 9. The pressure-type proportional valve 4, the flow-type proportional valve 5, the flow meter 6 and the pressure gauge 7 are all electrically connected to the programmable controller 8.

[0048] The programmable controller 8 is a PID programmable controller. The pressure-type proportional valve 4 is used to control and adjust the pressure of the gas source after high pressure-drying-precooling to ensure that the gas source entering the vortex tube element 901 is constant within the working pressure range; the flow-type proportional valve 5 controls the gas source flow rate at the input end of the vortex tube element 901 by inputting an electrical signal to make the gas source flow rate constant within the working flow range of the vortex tube element 901; the pressure gauge 7 can monitor the working pressure at the input end of the vortex tube refrigeration system 9 in real time, and can store the pressure data in real time, and further convert the pressure value into an electrical signal and input it into the PID programmable controller 8; the flow meter 6 can monitor and store the gas source flow rate at the input end of the vortex tube refrigeration system 9 in real time, and convert the end gas source flow value into an electrical signal and input it into the PID programmable controller 8; the PID programmable controller 8 can receive the electrical signals of the pressure-type proportional valve 4, the flow-type proportional valve 5, the pressure gauge 7 and the flow meter 6 in real time, and judge and regulate the gas source pressure and flow by collecting and comparing the signal values ​​of the pressure-type proportional valve 4 and the pressure gauge 7, and the signal values ​​of the flow-type proportional valve 5 and the flow meter 6.

[0049] like Figure 2As shown, the vortex tube refrigeration system 9 is mainly composed of a vortex tube component 901, a cold delivery pipe 902 and a vortex tube bracket 903; the vortex tube bracket 903 is placed on the ground, the vortex tube component 901 is placed on the vortex tube bracket 903, the output end of the vortex tube component 901 is connected to the input end of the sample chamber 10 through the cold delivery pipe 902, the cold delivery pipe 902 is connected to the output port of the vortex tube component 901 through a threaded joint, the vortex tube component 901 is a vortex tube component refrigeration element, and the vortex tube component 901 is a simple energy separation device with no internal Any moving parts require low energy consumption and only need to provide a high-pressure gas source to generate a low-temperature cold flow. The temperature of the low-temperature cold flow output by the vortex tube can be controlled by adjusting the opening of its own regulating valve; the vortex tube bracket 903 can support the vortex tube element 901 and adjust it according to the sample height; the cold delivery pipeline 902 is connected to the vortex tube element 901 through a threaded joint, and the cold flow output from the cold end of the vortex tube element 901 can be introduced into the sample cabin. The cold delivery pipeline 902 has a built-in insulation layer and the outer wall is wrapped with thermal insulation materials to reduce the heat consumption of the cold flow during pipeline transportation.

[0050] like Figure 2-Figure 3 As shown, the sample cabin 10 is mainly composed of a cold flow cabin 1001 with a cavity inside, a soil sample container 1003 with a cavity inside, and a steel support 1005; the soil sample container 1003 is placed on the ground, and the soil sample container 1003 is used to install the soil sample, and the soil sample is a prototype sample or a model sample. The cold flow cabin 1001 is placed on the soil sample container 1003 and the cold flow cabin 1001 and the soil sample container 1003 are fixedly connected by the steel support 1005 and bolts 1006. The lower surface of the cold flow cabin 1001 and the upper surface of the soil sample container 1003 are also connected by a flange connection structure 1007. After the soil sample is made and placed in the soil sample container 1003, the flange connection structure 1007 and the bolts 1006 can be used to fix the cold flow cabin 1001 and the soil sample container 1003. 06 The upper cold flow cabin 1001 and the lower soil sample container 1003 are connected and fixed. A plurality of exhaust holes 1002 and an air inlet are provided on the side wall of the cold flow cabin 1001. The air inlet, as the input end of the sample cabin 10, is connected to the cold delivery pipe 902 in the vortex tube refrigeration system 9 through a thread. The exhaust hole 1002 is connected to the outside atmosphere. The cold flow cabin 1001 is externally connected to a first temperature sensor. A plurality of sensor channels 1004 are provided on the side wall of the soil sample container 1003. An external second temperature sensor is buried in the soil sample in the soil sample container 1003 after passing through the sensor channel 1004. A water delivery channel 1010 is provided in the bottom plate of the soil sample container 1003. The water delivery channel 1010 is externally connected to an external water tank.

[0051] The first temperature sensor and the second temperature sensor are both electrically connected to the programmable controller 8 , and the first temperature sensor and the second temperature sensor are both thermocouple temperature sensors.

[0052] The air inlet is used to introduce the cold flow generated in the vortex tube refrigeration system 9 into the cavity of the upper cold flow chamber 1001, and the exhaust hole 1002 is used to discharge the excess cold flow entering the cavity of the cold flow chamber 1001, so that the internal air pressure of the cold flow chamber 1001 is the same as the actual air pressure. The sensor channel 1004 is used to monitor the temperature field in the sample chamber 10 in real time (the ambient temperature in the cold flow chamber (1001) and the internal temperature field of the soil sample). The second temperature sensor is passed into the sample chamber 10 through the sensor channel 1004 and extends into the soil sample. At the same time, in order to avoid the linear arrangement of the second temperature sensor, Second, the temperature sensors influence each other. The sensor channels 1004 are staggered in the vertical direction. The water supply channel 1010 can be connected to an external water tank. When conducting subsequent saturated soil test experiments, water enters the bottom of the sample cabin 10 through the bottom water supply pipe 1010, and the soil sample in the sample cabin 10 can be saturated. The soil sample is a normal gravity prototype sample or a super gravity model sample. The steel supports 1005 are distributed around the sample cabin 10 to provide lateral support for the sample cabin 10 in the super gravity test to prevent the sample cabin 10 from being damaged due to insufficient bearing capacity of the sample cabin 10 itself due to the increase of the super gravity g value.

[0053] The side wall of the soil sample container 1003 includes a first side wall and a second side wall. The first side wall is located inside the second side wall and a gap region, i.e., a sandwich layer, is provided between the first side wall and the second side wall. The first side wall and the second side wall are provided with openings at the same position. The sensor channel 1004 passes through the openings of the second side wall and the first side wall in sequence and is connected to the cavity in the soil sample container 1003. A vacuum hole 1008 is provided on the second side wall. The vacuum layer is connected to an external vacuum pump through the vacuum hole 1008. Since the vacuum layer is connected to an external vacuum pump through the vacuum hole 1008, the vacuum layer is connected to an external vacuum pump through the vacuum hole 1008. During the process, there is a temperature difference between the internal temperature of the sample cabin 10 and the external ambient temperature. In order to avoid lateral thermal erosion of the internal sample caused by the external temperature difference during the test, a vacuum insulation layer 1009 is provided on the outside of the soil sample container 1003. The vacuum insulation layer 1009 is a vacuum hole 1008 reserved on the outer wall of the soil sample container 1003. Before the start of the test, a vacuum pump is connected to the vacuum hole 1008 to evacuate the interlayer, thereby forming a vacuum interlayer between the two walls to ensure that the unidirectional freezing of the soil sample is not affected by lateral thermal erosion.

[0054] The cold flow chamber 1001 and the soil sample container 1003 are both made of acrylic material, so that the cold flow chamber 1001 and the soil sample container 1003 have the characteristics of low thermal conductivity and high strength.

[0055] The simulation test for verifying the time similarity law of high-gravity earth-air convection heat transfer requires the preparation of normal gravity prototype samples and high-gravity model samples in the corresponding sample chamber 10, and by providing a continuous and stable cold flow on the surface of the soil, the cold flow and the soil undergo convection heat exchange, thereby changing the internal temperature field distribution of the prototype and model samples, and finally by comparing the internal temperature fields of the prototype sample under normal gravity and the model sample under high gravity, the time similarity law of earth-air convection heat transfer between the two can be determined. The following takes the normal gravity and 10g high-gravity dry soil model tests as examples, and further explains the present invention in combination with the accompanying drawings and implementation steps:

[0056] The following steps are involved:

[0057] Step 1. According to the geometric similarity law of supergravity, the geometric dimensions of the soil sample are determined using the scale ratio. If the supergravity selected for the test is 10g, the scale ratio between the model sample and the prototype sample is 1:10. If the supergravity selected for the test is 20g, the scale ratio between the model sample and the prototype sample is 1:20, and so on. According to the preset soil sample size, a prototype sample and several model samples with different scale ratios are made. The soil sample is a prototype sample or a model sample. In the specific implementation, the size of the constant gravity prototype sample is (height H = 1000mm, diameter D = 100mm), the size of the 10g supergravity model sample is (height H = 100mm, D = 100mm), and the size of the 20g supergravity model sample is (height H = 50mm, D = 100mm). The test is a one-dimensional heat transfer problem in the depth direction, so the diameter does not need to be scaled. The prototype sample is placed in the soil. Eleven second temperature sensors are arranged in the sample container 1003, and on the soil sample container 1003. In the specific implementation, each second temperature sensor is spaced 100 mm apart. To avoid the second temperature sensors from influencing each other, they are staggered in the vertical direction. Then the cold flow chamber 1001 is installed on the soil sample container 1003 and connected with the flange connection structure 1007. Finally, the side wall of the soil sample container 1003 is connected with a vacuum pump, and the vacuum pump is used to vacuum the sandwich layer in the soil sample container 1003 so that a vacuum sandwich layer is formed between the two side walls.

[0058] Step 2: After vacuum extraction is completed, the air compressor 1 is used to generate a compressed air source, and the compressed air source is converted into a cold flow after passing through the dryer 2, the precooler 3, the airflow feedback control system and the vortex tube refrigeration system 9 in sequence;

[0059] Step 2 is specifically as follows: after completing the vacuum extraction, start the air compressor 1 so that a high-pressure compressed air source with sufficient flow is generated in the air compressor 1, and the generated compressed air source is successively input into the dryer 2 and the precooler 3 through the gas pipeline to obtain a dry low-temperature air source. The dryer 2 can remove water from the compressed air source to make it dry, and the fully dried compressed air source is then introduced into the precooler 3 to cool the compressed air source to a specified temperature to preliminarily obtain a high-pressure-dry-low-temperature air source that meets the test requirements, and then the dry low-temperature air source is introduced into the airflow feedback control system: the pressure proportional valve 4 and the flow proportional valve 5 are used to adjust the pressure and flow of the dry cold air source in real time, and the pressure gauge 6 and the flow meter 7 are used to monitor the pressure and flow of the dry cold air source in real time. When the pressure and flow of the dry low-temperature air source reach the preset pressure value and flow value of the test respectively and reach stability, the dry low-temperature air source is introduced into the vortex tube element 901, and the vortex tube element 901 converts the dry low-temperature air source into a constant temperature and uniform speed cold flow.

[0060] In order to keep the airflow entering the vortex tube refrigeration system 9 at a constant pressure and flow, the air source entering the vortex tube refrigeration system 9 needs to be monitored and regulated in real time by the pressure proportional valve 4, the flow proportional valve 5, the flow meter 7 and the pressure gauge 6. Before the test starts, the pressure proportional valve 4 and the flow proportional valve 5 are set to 0.7MPa and 1000L / min respectively by the programmable controller 8 (determined according to the model parameters of the vortex tube 901 element at the rear end); after the dry cold air source is regulated by the pressure proportional valve 4 and the flow proportional valve 5, the pressure gauge 6 and the flow meter 7 are used to monitor the air source pressure and flow at the input end of the vortex tube refrigeration system 9 in real time; during the test, when the monitoring values ​​of the pressure gauge 6 and the flow meter 7 are the initial setting values, the whole system operates normally; when the monitoring value exceeds the initial setting value by ±5%, the PID programmable controller 8 will identify the values ​​of the pressure gauge 6 and the flow meter 7, and send a control signal to the pressure proportional valve 4 and the flow proportional valve 5 to ensure that the vortex tube refrigeration system 9 is in a constant state during the test.

[0061] Step 3: Conduct a constant gravity simulation test

[0062] The cold flow generated in step 2 is passed into the cold flow chamber 1001 of the sample chamber 10 containing the prototype sample through the cold delivery pipe 902, and the temperature in the cold flow chamber 1001 is monitored by the pressure proportional valve 4, the flow proportional valve 5 and the first temperature sensor. After reaching the preset temperature threshold, the temperature field of the prototype sample is obtained by the second temperature sensor;

[0063] Step 4: Conduct hypergravity simulation test

[0064] After the preset test time, the soil sample is taken out from the soil sample container 1003, and then a new model sample is placed in the soil sample container 1003. The position of the second temperature sensor on the soil sample container 1003 is adjusted so that the second temperature sensor is placed at the preset position. Since the test is a single-term freezing and a one-dimensional heat transfer problem, the height dimensions of the prototype sample and the model sample and the arrangement of the internal temperature sensors must conform to the hypergravity geometric similarity scale during sample preparation. In specific implementation, if the hypergravity selected for the test is 10g, the interval between each thermocouple temperature sensor is 10mm; if the hypergravity selected for the test is 20g, the interval between each thermocouple temperature sensor is 5mm. The cold flow cabin 1001 is fixedly installed and then a vacuum pump is used to vacuum extract the sandwich layer in the soil sample container 1003.

[0065] The sample cabin 10 containing the model sample is placed in the hanging basket of the centrifuge, and the gravity value of the centrifuge is controlled to reach a preset gravity value. If the supergravity selected for the test is 10g, the gravity value of the centrifuge is controlled to reach a preset 10g and the centrifuge runs stably under the supergravity of 10g; if the supergravity selected for the test is 20g, the gravity value of the centrifuge is controlled to reach a preset 20g and the centrifuge runs stably under the supergravity of 10g, and the cold flow generated in step 2 is passed into the cold flow cabin 1001 of the sample cabin 10 containing the model sample through the cold delivery pipeline 902, and after the temperature in the cold flow cabin 1001 is monitored by the pressure type proportional valve 4, the flow type proportional valve 5 and the first temperature sensor to reach the preset temperature threshold, the temperature field of the model sample is obtained by the second temperature sensor;

[0066] In step 3 and step 4, the temperature in the cold flow chamber 1001 is monitored by the pressure type proportional valve 4, the flow type proportional valve 5 and the first temperature sensor. After reaching the preset temperature threshold, the temperature field of the soil sample is obtained by the second temperature sensor. The specific steps are: the temperature of the cold flow chamber 1001 is regulated by the pressure type proportional valve 4 and the flow type proportional valve 5, and the temperature in the cold flow chamber 1001 is monitored in real time by the first temperature sensor. When the temperature of the cold flow chamber 1001 reaches the preset temperature threshold, the second temperature sensor is used to monitor and record the temperature of the soil sample in real time. The temperature at the same depth is used to obtain the temperature field of the soil sample. In specific implementation, after the cold flow enters the cold flow cabin 1001, the air temperature in the cold flow cabin 1001 is reduced and controlled at -15°C, and the excess cold flow is discharged from the exhaust hole 1002 to ensure the stability of the air pressure in the sample cabin 10. The continuous introduction of the cold flow realizes the convective heat exchange process between the soil sample in the sample cabin 10 and the upper cold flow. The lower soil sample and the upper cold flow continuously exchange heat by convection, and the internal temperature field of the soil sample gradually changes. The changing temperature of the soil sample is monitored and stored in real time by the internal second temperature sensor.

[0067] Step 5, repeat step 4 multiple times to obtain the temperature field of the model specimen at different scale ratios;

[0068] Step 6. After the hypergravity simulation test and the normal gravity simulation test are completed, the temperature field of the model sample at each scale ratio is compared with the temperature field of the prototype sample to obtain the time similarity law of ground-air convection heat transfer of the model sample and the prototype sample, thereby realizing the analysis and calculation of the frozen soil moisture field and temperature field under real conditions.

[0069] To verify the validity of the time similarity law of earth-air convective heat transfer under different g values, simply use the above device and method to repeat the above steps under different hypergravity g values.

[0070] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A high gravity earth-air convection heat transfer similarity law verification test device, characterized by: It comprises an air source supply system, an airflow feedback control system, a vortex tube refrigeration system (9) and a sample chamber (10); the input end of the air source supply system is connected to the outside atmosphere, the output end of the air source supply system is connected to the input end of the airflow feedback control system through a pipeline, the output end of the airflow feedback control system is connected to the input end of the vortex tube refrigeration system (9) through a pipeline, and the output end of the vortex tube refrigeration system (9) is connected to the input end of the sample chamber (10); The air source supply system is mainly composed of an air compressor (1), a dryer (2) and a precooler (3); The airflow feedback control system is mainly composed of a pressure-type proportional valve (4), a flow-type proportional valve (5), a flow meter (6), a pressure gauge (7), and a programmable controller (8); The vortex tube refrigeration system (9) is mainly composed of a vortex tube component (901), a cold delivery pipe (902) and a vortex tube bracket (903); the vortex tube bracket (903) is placed on the ground, the vortex tube component (901) is placed on the vortex tube bracket (903), and the output end of the vortex tube component (901) is connected to the input end of the sample chamber (10) through the cold delivery pipe (902); The sample cabin (10) is mainly composed of a cold flow cabin (1001) with a cavity inside, a soil sample container (1003) with a cavity inside, and a steel support (1005); the soil sample container (1003) is placed on the ground, the soil sample container (1003) is used to install the soil sample, the cold flow cabin (1001) is placed on the soil sample container (1003), and the cold flow cabin (1001) and the soil sample container (1003) are fixedly connected via the steel support (1005); a plurality of exhaust holes (1002) and an air inlet are opened on the side wall of the cold flow cabin (1001), and the air inlet The air port, as the input end of the sample chamber (10), is connected to the cold delivery pipe (902) in the vortex tube refrigeration system (9), and the exhaust hole (1002) is connected to the outside atmosphere. The cold flow chamber (1001) is externally connected to a first temperature sensor. A plurality of sensor channels (1004) are provided on the side wall of the soil sample container (1003). An external second temperature sensor passes through the sensor channel (1004) and is buried in the soil sample in the soil sample container (1003). A water delivery channel (1010) is provided in the bottom plate of the soil sample container (1003), and the water delivery channel (1010) is externally connected to an external water tank.

2. The high gravity earth-air convection heat transfer similarity law verification test device according to claim 1, characterized in that: The input end of the air compressor (1) is connected to the outside atmosphere, the output end of the air compressor (1) is connected to the input end of the dryer (2) through a pipeline, the output end of the dryer (2) is connected to the input end of the precooler (3) through a pipeline, the output end of the dryer (2) is connected to the input end of the precooler (3) through a pipeline, and the output end of the precooler (3) is connected to the input end of the airflow feedback control system through a pipeline; One end of the pressure-type proportional valve (4) is connected to the precooler (3) as the input end of the airflow feedback control system, and the other end of the pressure-type proportional valve (4) is connected to one end of the flow meter (6) through a pipeline. A flow-type proportional valve (5) is provided on the pipeline from the pressure-type proportional valve (4) to the flow meter (6), and the other end of the flow meter (6) is respectively connected to the pressure gauge (7) and the input end of the vortex tube refrigeration system (9). The pressure-type proportional valve (4), the flow-type proportional valve (5), the flow meter (6) and the pressure gauge (7) are all electrically connected to the programmable controller (8).

3. The high gravity earth-air convection heat transfer similarity law verification test device according to claim 1, characterized in that: The side wall of the soil sample container (1003) comprises a first side wall and a second side wall, the first side wall is located inside the second side wall and a sandwich layer is provided between the first side wall and the second side wall, the first side wall and the second side wall are provided with openings at the same position, the sensor channel (1004) passes through the openings of the second side wall and the first side wall in sequence and is connected to the cavity in the soil sample container (1003), a vacuum hole (1008) is provided on the second side wall, and the vacuum layer is connected to an external vacuum pump through the vacuum hole (1008).

4. The high gravity earth-air convection heat transfer similarity law verification test device according to claim 1, characterized in that: The cold flow chamber (1001) and the soil sample container (1003) are both made of acrylic material.

5. The high gravity earth-air convection heat transfer similarity law verification test device according to claim 1, characterized in that: The first temperature sensor and the second temperature sensor are both electrically connected to the programmable controller (8), and the first temperature sensor and the second temperature sensor are both thermocouple temperature sensors.

6. A heat transfer similarity law verification simulation method applied to the device described in any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, respectively making a prototype sample and a plurality of model samples of different scale ratios according to a preset soil sample size, wherein the soil sample is a prototype sample or a model sample, placing the prototype sample in a soil sample container (1003), and arranging eleven second temperature sensors on the soil sample container (1003), then installing a cold flow chamber (1001) on the soil sample container (1003), and finally connecting the side wall of the soil sample container (1003) to a vacuum pump, and using the vacuum pump to vacuum extract the sandwich layer in the soil sample container (1003); Step 2: After vacuum extraction is completed, an air compressor (1) is used to generate a compressed air source, and the compressed air source is converted into a cold flow after passing through a dryer (2), a precooler (3), an airflow feedback control system and a vortex tube refrigeration system (9); Step 3: Conduct a constant gravity simulation test The cold flow generated in step 2 is passed through a cold delivery pipe (902) into a cold flow chamber (1001) of a sample chamber (10) containing a prototype sample, and after the temperature in the cold flow chamber (1001) is monitored by a pressure proportional valve (4), a flow proportional valve (5) and a first temperature sensor and reaches a preset temperature threshold, a temperature field of the prototype sample is obtained by a second temperature sensor; Step 4: Conduct hypergravity simulation test After a preset test time, the soil sample is taken out of the soil sample container (1003), a new model sample is placed in the soil sample container (1003), the position of the second temperature sensor on the soil sample container (1003) is adjusted so that the second temperature sensor is placed at a preset position, the cold flow chamber (1001) is fixedly installed, and then a vacuum pump is used to vacuum extract the sandwich layer in the soil sample container (1003); The sample chamber (10) containing the model sample is placed in the hanging basket of the centrifuge, the gravity value of the centrifuge is controlled to reach a preset gravity value, the cold flow generated in step 2 is passed through the cold delivery pipe (902) into the cold flow chamber (1001) of the sample chamber (10) containing the model sample, and the temperature in the cold flow chamber (1001) is monitored by using a pressure proportional valve (4), a flow proportional valve (5) and a first temperature sensor. After reaching a preset temperature threshold, the temperature field of the model sample is obtained by using a second temperature sensor; Step 5, repeat step 4 multiple times to obtain the temperature field of the model specimen at different scale ratios; Step 6. After the hypergravity simulation test and the normal gravity simulation test are completed, the temperature field of the model sample at each scale ratio is compared with the temperature field of the prototype sample to obtain the time similarity law of ground-air convection heat transfer of the model sample and the prototype sample, thereby realizing the analysis and calculation of the frozen soil moisture field and temperature field under real conditions.

7. A heat transfer similarity law verification simulation method according to the device of claim 6, characterized in that: The step 2 is specifically as follows: after completing the vacuum extraction, the air compressor (1) is started to generate a compressed air source in the air compressor (1); the generated compressed air source is sequentially input into the dryer (2) and the precooler (3) through a pipeline to obtain a dry low-temperature air source; and the dry low-temperature air source is introduced into the airflow feedback control system: the pressure and flow of the dry cold air source are adjusted in real time by using a pressure proportional valve (4) and a flow proportional valve (5); and the pressure and flow of the dry cold air source are monitored in real time by using a pressure gauge (6) and a flow meter (7); when the pressure and flow of the dry low-temperature air source reach the pressure value and flow value preset in the test, respectively, the dry low-temperature air source is introduced into the vortex tube element (901); and the vortex tube element (901) converts the dry low-temperature air source into a cold flow.

8. A heat transfer similarity law verification simulation method according to the device of claim 6, characterized in that: In step 3 and step 4, after the temperature in the cold flow chamber (1001) is monitored by using the pressure-type proportional valve (4), the flow-type proportional valve (5) and the first temperature sensor to reach a preset temperature threshold, the temperature field of the soil sample is obtained by using the second temperature sensor. The specific steps are: the temperature of the cold flow chamber (1001) is regulated by using the pressure-type proportional valve (4) and the flow-type proportional valve (5), and the temperature in the cold flow chamber (1001) is monitored in real time by using the first temperature sensor; when the temperature of the cold flow chamber (1001) reaches a preset temperature threshold, the temperature of the soil sample at different depths is monitored and recorded in real time by using the second temperature sensor to obtain the temperature field of the soil sample.

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