Intrusive in situ measurement device and method for the thermal conductivity coefficient at a point in soil.

Abstract

An intrusive, in situ measurement device and method for the thermal conductivity coefficient at a point in soil is disclosed. The device includes an insulating probe inserted vertically into soil, an annular heating tube located at the end of the insulating probe, an insulating penetration head located at the end of the annular heating tube, a temperature sensor located on the outer wall of the annular heating tube for measuring the soil temperature at a point, a power source for supplying a constant heating power to the annular heating tube, and a temperature collection system for receiving the temperature value measured by the temperature sensor and calculating the thermal conductivity coefficient of the soil at the depth where the annular heating tube is located. The present invention solves the technical problem of the prior art that the thermal conductivity coefficient of a point of in-situ soil cannot be obtained conveniently and accurately.

Description

[Technical field]

[0001] The present invention relates to the field of geological sensing technology, and in particular to an intrusive in-situ measuring device and method for the thermal conductivity coefficient at a point in soil. [Background technology]

[0002] The thermal conductivity coefficient of rock and soil is one of the important indicators that reflect its thermophysical properties, and its magnitude characterizes the thermal conductivity ability of soil. The thermal conductivity coefficient of soil is an important influencing factor of the movement of pollutants, moisture and heat transmission and temperature information changes in important regions of the earth. On the one hand, accurate measurement of the thermal conductivity coefficient of soil serves the development of shallow geothermal energy, the control of soil pollution and the construction of cold region engineering, and on the other hand, it helps the research of the theory and model of water-heat change in soil, and can indirectly obtain parameters such as soil moisture content and pollutant content. The thermal conductivity coefficient of soil is mainly affected by factors such as soil quality, moisture content, temperature, porosity and salt content.

[0003] At present, the methods for obtaining the thermal conductivity coefficient of soil mainly include indoor testing, in-situ testing, and prediction modeling. The indoor testing method mainly involves obtaining soil samples on-site, then transferring them to the laboratory to perform thermal conductivity coefficient testing on the soil samples using the protective hot plate method (such as patent CN107589147A). The limitations of this method are that the sampling and transportation process takes time and effort, and the whole process is prone to perturbation of the soil sample, which results in large errors in the test results. The in-situ testing method mainly involves the hot wire method (such as patent CN109884115A and CN107727687A) and the in-situ thermal response testing method (such as patent CN102721722A) to perform in-situ testing of the thermal conductivity coefficient of soil. The basic principle of these two types of testing methods is the theory of an infinitely long instantaneous line heat source, which uses a line heat source to heat the soil, which has a large range of influence, and can only obtain the average thermal conductivity coefficient of the soil within this range, and cannot obtain the thermal conductivity coefficient of a certain point at a certain depth of the soil, which is affected by the heterogeneity of the soil and has a large error. The predictive model method (e.g., Patents CN113075250A and CN109117452A) estimates the thermal conductivity coefficient of soil based on an empirical model or a theoretical model, and the thermal conductivity coefficient can be obtained by substituting the basic physical indicators of soil into the corresponding predictive model. However, the calculation of the predictive model is complicated, the usage cost is high, and there is a large difference in the physical composition of different types of soil. Therefore, the application range of the predictive model method is small, and the error of the prediction result is large.

[0004] Therefore, there is an urgent need to solve the above problem. Summary of the Invention [Problem to be solved by the invention]

[0005] Objective of the invention: The first objective of the present invention is to provide an intrusive in-situ measuring device for the thermal conductivity coefficient at a point in soil, in order to solve the technical problem of being unable to conveniently and accurately obtain the thermal conductivity coefficient at a point in soil.

[0006] A second object of the present invention is to provide a method for measuring the thermal conductivity of soil at a point using an intrusive in-situ measuring device. [Means for solving the problem]

[0007] Technical solution: In order to achieve the above objectives, the present invention discloses an in-situ intrusive measuring device for the thermal conductivity coefficient of soil at a certain point, which includes: an insulating probe vertically inserted into the soil; an annular heating tube located at the end of the insulating probe; an insulating penetration head located at the end of the annular heating tube; a temperature sensor located on the outer wall of the annular heating tube and for measuring the soil temperature at a certain point; a power source for supplying a constant heating power to the annular heating tube; and a temperature collection system for receiving the temperature value measured by the temperature sensor and calculating the thermal conductivity coefficient of the soil at the depth where the annular heating tube is located.

[0008] The constant heating power output by the power source is P1, and the thermal conductivity λ of the soil at the depth where the annular heating tube is located calculated by the temperature collection system is as follows:

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[0009] Preferably, the power supply is a DC constant voltage power supply with a heating power range of 0 to 15 W and a control accuracy of ±0.5% FS.

[0010] In addition, a heat insulating coating layer made of heat-blocking heat insulating paint is applied to the surfaces of the heat insulating probe and the heat insulating penetration head, and the heat conductivity coefficient of the heat insulating coating layer is 0.03 W / (m·℃) or less.

[0011] Furthermore, the outer diameter and height of the annular heating tube are equal, and the height of the annular heating tube is 5 cm or less.

[0012] Preferably, the insulated probe, the annular heating tube and the insulated penetration head form a rigid body which is inserted into the soil, the annular heating tube being at a measurement depth required for the thermal conductivity coefficient in the soil.

[0013] Additionally, a power source is connected to the annular heating tube via a power line passing through the insulating probe, and the temperature acquisition system is connected to a temperature sensor via a data line passing through the insulating probe.

[0014] Additionally, the outer diameter of the insulated probe and the insulated penetration head is the same as the outer diameter of the annular heating tube, and the end of the insulated penetration head is tapered.

[0015] Preferably, the measurement range of the temperature sensor is 20 to 150°C, with an accuracy of ±0.5°C.

[0016] The present invention relates to a method for measuring the thermal conductivity of a soil at a point using an intrusive in-situ measuring device, comprising the steps of: Attaching a temperature sensor to the outer wall of the annular heating tube, connecting the insulating probe, the annular heating tube and the insulating penetration head in sequence as a rigid body, connecting the annular heating tube and a power source through a power line, and connecting the temperature sensor and a temperature collection system through a data line; inserting the annular heating tube vertically into the soil target depth to be tested; After the temperature collection system reading has stabilized, recording the soil temperature value T0 measured by the temperature sensor at this time; A step of turning on the power supply and controlling the heating power output to the annular heating tube to a constant power value P1; After the temperature collection system reading has restabilized, recording the soil temperature value T1 measured by the temperature sensor at this time; The constant heating power value P1 of the annular heating tube, the soil temperature value T0 measured by the temperature sensor before heating, and the soil temperature value T1 measured by the temperature sensor after heating is stabilized are substituted into the following equation to obtain the thermal conductivity coefficient λ of the soil:

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[0017] Invention principle: The present invention regards the annular heating tube as a spherical heat source, and based on Fourier's heat conduction law and the law of conservation of energy, finds that the temperature of the soil at the outer wall of the annular heating tube under soil steady-state heat conduction is only related to the heating power and the thermal conductivity coefficient of the soil. Effect of the Invention

[0018] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) In contrast to the problem that conventional in-situ testing technology can only measure the average thermal conductivity coefficient of a soil layer based on the theory of a line heat source, the present invention can measure the thermal conductivity coefficient at a certain point in the soil based on the steady-state heat conduction model of a spherical heat source in the soil, which has a wider range of applications and can provide more accurate test parameters for geothermal resource development, soil pollution control, and cold region construction.

[0020] (2) The present invention only requires measuring the soil temperature and corresponding heating power before and after heating is stabilized at a certain point in the soil, and obtains the thermal conductivity coefficient through calculation, thereby avoiding the analytical error caused by the time period in which traditional in-situ testing technology selects fitting experimental data.

[0021] (3) The present invention heats the soil through a small-sized annular heating tube, and the heating influence range is significantly smaller than that of the linear heat source adopted by the conventional in-situ testing technology, which significantly reduces the test error caused by the heterogeneity of the soil.

[0022] (4) The present invention adopts a thermally insulated probe and a thermally insulated penetration head, which avoids the thermal conduction of the device itself from interfering with the soil thermal conductivity coefficient test.

[0023] (5) The present invention has low production costs, is easy to operate, and is convenient to carry, which not only avoids the cumbersome and time-consuming process of sampling and transporting to a laboratory for testing, but also eliminates the need for huge costs in building on-site testing facilities. [Brief description of the drawings]

[0024] [Figure 1] FIG. 2 is a structural schematic diagram of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The technical solution of the present invention will be further described below with reference to the drawings.

[0026] As shown in FIG. 1, the present invention discloses an intrusive in-situ measurement device for thermal conductivity coefficient at a point of soil, including a power source 1, a temperature collection system 2, a power line 3, a data line 4, an adiabatic probe 5, an annular heating tube 6, a temperature sensor 7 and an adiabatic penetration head 8. The power source 1 is a DC constant voltage power source with a heating power range of 0-15W and a control accuracy of ±0.5%FS. The power source 1 provides a constant heating power to the annular heating tube 6 through the power line 3, the power line 3 penetrates and penetrates the top of the adiabatic probe 5 to connect to the annular heating tube 6, the top and bottom of the annular heating tube 6 are respectively connected to the adiabatic probe 5 and the adiabatic penetration head 8 by threads, and the annular heating tube 6 is made of titanium alloy stainless steel material, has the same outer diameter and height, and is 4cm high. The insulation probe 5 and the insulation penetration head 8 are made of cast iron material, the outer diameter of the insulation probe 5 and the insulation penetration head 8 is the same as the outer diameter of the annular heating tube 6, the end of the insulation penetration head 8 is tapered, the insulation probe can be adjusted according to the design depth, including but not limited to using one insulation probe, and multiple insulation probes can be connected by screws. The surface of the insulation probe 5 and the insulation penetration head 8 is coated with an insulation coating layer made of heat-blocking heat-insulating paint, and the thermal conductivity coefficient of the insulation coating layer is 0.03W / (m·℃) or less. The temperature collection system 2 reads the temperature value measured by the temperature sensor 7 through the data line 4, the data line 4 penetrates and penetrates the top of the insulation probe 5, and then protrudes from the side wall of the insulation probe 5 and is connected to the temperature sensor 7, the temperature sensor 7 is attached to the outer wall of the annular heating tube 6, the measurement range is -20~150℃, and the accuracy is ±0.5℃. The temperature collection system 2 is an instrument with a calculation function. A rigid body consisting of the insulating probe 5, the annular heating tube 6 and the insulating penetration head 8 is inserted vertically into the soil, the annular heating tube 6 being at the measurement depth required for the thermal conductivity coefficient in the soil.

[0027] The constant heating power output by the power source 1 is P1, and the thermal conductivity coefficient λ of the soil at the depth where the annular heating tube is located calculated by the temperature collection system 2 is as follows:

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[0028] The present invention relates to a method for measuring the thermal conductivity of a soil at a point using an intrusive in-situ measuring device, comprising the steps of: Attaching a temperature sensor to the outer wall of the annular heating tube, connecting the insulating probe, the annular heating tube and the insulating penetration head in sequence as a rigid body, connecting the annular heating tube and a power source through a power line, and connecting the temperature sensor and a temperature collection system through a data line; Inserting the annular heating tube vertically into the soil target depth to be tested (which is 1.5 meters deep); After the temperature collection system reading has stabilized, record the soil temperature value T0 (T0=22° C.) measured by the temperature sensor at this time; A step of turning on the power supply and controlling the heating power output to the annular heating tube to a constant power value P1 (P1=5 W); After the temperature collection system reading has stabilized again, record the soil temperature value T1 (T1=34° C.) measured by the temperature sensor at this time; The constant heating power value P1 of the annular heating tube, the soil temperature value T0 measured by the temperature sensor before heating, and the soil temperature value T1 measured by the temperature sensor after heating is stabilized are substituted into the following equation to obtain the thermal conductivity coefficient λ of the soil:

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[0029] As is evident from the above implementation, the test process of the present invention is simple and rapid; by simply measuring the soil temperature and the corresponding heating power at a certain point of the soil before heating and after the heating has stabilized, the thermal conductivity coefficient of the soil at this point can be obtained by simple calculation. Compared with the prior art, the present invention has the characteristics of low cost, simple operation, and reliable test results, and has extremely high application value in engineering.

[0030] Although the preferred embodiments of the present invention have been described in detail above, the design concept of the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical concept of the present invention, and all of these equivalent transformations fall within the scope of protection of the present invention.

Claims

1. 1. An intrusive in-situ measurement device for the thermal conductivity coefficient at a point in soil, comprising: The method includes an insulating probe (5) inserted vertically into the soil, an annular heating tube (6) located at the end of the insulating probe, an insulating penetration head (8) located at the end of the annular heating tube, a temperature sensor (7) located on the outer wall of the annular heating tube for measuring the soil temperature at a certain point, a power source (1) for supplying a constant heating power to the annular heating tube, and a temperature collection system (2) for receiving the temperature values ​​measured by the temperature sensor and calculating the thermal conductivity coefficient of the soil at the depth where the annular heating tube is located. The constant heating power output by the power source (1) is P １ and the thermal conductivity coefficient λ of the soil at the depth where the annular heating pipe is located calculated by the temperature collection system (2) is as follows: [0050] In the formula, λ is the thermal conductivity coefficient of the soil, and P １ is the heating power value of the annular heating tube, and d ０ is the outer diameter of the annular heating tube, and T ０ is the temperature value of the soil measured by the temperature sensor before heating, and T １ is the soil temperature value measured by the temperature sensor after heating has stabilized. An intrusive in-situ measurement device for the thermal conductivity coefficient at a point in the soil.

2. The intrusive in-situ measurement device for thermal conductivity coefficient at a point of soil according to claim 1, characterized in that the power source (1) is a DC constant voltage power source with a heating power range of 0-15W and a control accuracy of ±0.5% FS.

3. The intrusive in-situ measuring device for the thermal conductivity coefficient at a certain point of soil as described in claim 1, wherein the surfaces of the insulation probe (5) and the insulation penetration head (8) are coated with an insulation coating layer made of a heat-transfer-blocking type insulation paint, and the thermal conductivity coefficient of the insulation coating layer is 0.03 W / (m·℃) or less.

4. 2. The intrusive in-situ measuring device for the thermal conductivity coefficient at a point of soil as claimed in claim 1, characterized in that the outer diameter and height of the annular heating tube (6) are equal, and the height of the annular heating tube is less than 5 cm.

5. 2. The intrusive in-situ measuring device for the thermal conductivity coefficient at a point in soil according to claim 1, characterized in that the adiabatic probe (5), the annular heating tube (6) and the adiabatic penetration head (8) form a rigid body and are inserted into the soil, the annular heating tube (6) being at a measuring depth required for the thermal conductivity coefficient in the soil.

6. 2. The intrusive in-situ measuring device for the thermal conductivity coefficient at a point in soil according to claim 1, characterized in that the power supply (1) is connected to an annular heating tube (6) via a power supply line (3) passing through the insulating probe, and the temperature acquisition system (2) is connected to a temperature sensor (7) via a data line (4) passing through the insulating probe.

7. 2. The intrusive in-situ measuring device for the thermal conductivity coefficient at a point in soil according to claim 1, characterized in that the outer diameter of the adiabatic probe (5) and the adiabatic penetration head (8) is the same as the outer diameter of the annular heating tube (6), and the end of the adiabatic penetration head (8) is tapered.

8. 2. The intrusive in-situ measuring device for the thermal conductivity coefficient at a point of soil according to claim 1, characterized in that the measuring range of the temperature sensor (7) is 20-150 °C and the accuracy is ±0.5 °C.

9. Attaching a temperature sensor to the outer wall of the annular heating tube, connecting the insulating probe, the annular heating tube and the insulating penetration head in sequence as a rigid body, connecting the annular heating tube and a power source through a power line, and connecting the temperature sensor and a temperature collection system through a data line; inserting the annular heating tube vertically into the soil target depth to be tested; After the temperature collection system reading has stabilized, the soil temperature value T measured by the temperature sensor at this time is ０ and recording The power supply is turned on, and the heating power output to the annular heating tube is set to a constant power value P １ and After the temperature collection system reading has stabilized again, the soil temperature value T measured by the temperature sensor at this time is １ and recording A constant heating power value P of the annular heating tube １ , the soil temperature value T measured by the temperature sensor before heating ０ and the soil temperature value T measured by the temperature sensor after the heating stabilizes. １ Substituting into the following equation to obtain the thermal conductivity coefficient λ of the soil, [006] In the formula, λ is the thermal conductivity coefficient of the soil, and d ０ is the outer diameter value of the annular heating tube.

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