CN212514369U - Optical fiber Bragg grating sensor for measuring soil moisture content - Google Patents
Optical fiber Bragg grating sensor for measuring soil moisture content Download PDFInfo
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- CN212514369U CN212514369U CN202021265860.5U CN202021265860U CN212514369U CN 212514369 U CN212514369 U CN 212514369U CN 202021265860 U CN202021265860 U CN 202021265860U CN 212514369 U CN212514369 U CN 212514369U
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- 239000002689 soil Substances 0.000 title claims abstract description 56
- 239000013307 optical fiber Substances 0.000 title claims abstract description 39
- 239000000523 sample Substances 0.000 claims abstract description 42
- 238000005485 electric heating Methods 0.000 claims abstract description 28
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 21
- 239000011229 interlayer Substances 0.000 claims abstract description 3
- 238000010438 heat treatment Methods 0.000 claims description 32
- 239000000835 fiber Substances 0.000 claims description 25
- 238000001514 detection method Methods 0.000 claims description 13
- 229920002635 polyurethane Polymers 0.000 claims description 12
- 239000004814 polyurethane Substances 0.000 claims description 12
- 239000011810 insulating material Substances 0.000 claims description 10
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 6
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- 239000010963 304 stainless steel Substances 0.000 description 2
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 description 2
- 229910000589 SAE 304 stainless steel Inorganic materials 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 229910052731 fluorine Inorganic materials 0.000 description 2
- 239000011737 fluorine Substances 0.000 description 2
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- 230000005540 biological transmission Effects 0.000 description 1
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- 229910000623 nickel–chromium alloy Inorganic materials 0.000 description 1
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Abstract
The utility model discloses an optical fiber Bragg grating sensor for measuring the water content of soil, which comprises a probe, an optical fiber Bragg grating, a soft cable type electric heating element, a cylinder shell inner wall, a cylinder shell outer wall and a cylinder top; wherein, the inner wall of the cylinder shell, the outer wall of the cylinder shell and the top of the cylinder form a cylinder with an opening at one end, one end of the probe positioned at the central shaft of the cylinder is fixedly connected with the bottom of the top of the cylinder, and the other end of the probe is used as a free end and is provided with a needle point; the inner side of the probe tube is provided with a groove for placing the optical fiber Bragg grating, and the optical fiber Bragg grating is led out from the probe tube through an optical fiber; the flexible cable type electric heating element is spirally wound between the inner wall of the cylinder shell and the outer wall of the cylinder shell to form an interlayer and is led out through a temperature-resistant flexible wire. The utility model discloses can heat the soil sample in the drum, utilize the sensor to measure coefficient of heat conductivity, can confirm the moisture content that corresponds according to the relation of soil moisture content and soil heat conductivity.
Description
Technical Field
The utility model relates to a measure optic fibre Bragg grating sensor of soil moisture content belongs to photoelectron measuring device technical field.
Background
The change of the soil moisture content can affect the stability of buildings, the subsidence and fission of roadbed and road surfaces, the flow of underground water and other characteristics. The measurement of the water content of the soil has important significance in the research and application fields of geology, soil science, remote sensing exploration, road traffic, environmental monitoring and the like. Scientists or engineers can obtain a great deal of useful information by continuously and constantly monitoring the soil moisture content, thereby providing important basis for the evaluation of environmental conditions. The conventional common moisture content measuring method generally has the problems of low measurement applicability, high cost and the like, and a low-cost moisture content measuring method or tool which can better meet the requirements on comprehensive performance such as stability, durability and the like does not exist.
When the water content of the soil is monitored by adopting the optical fiber Bragg grating sensor, the structure and the installation of the sensor need to be considered.
Disclosure of Invention
The utility model provides a measure optic fibre Bragg grating sensor of soil moisture content to be used for solving structure, the installation problem that is used for carrying out moisture content measuring optic fibre Bragg grating sensor.
The technical scheme of the utility model is that: a fiber Bragg grating sensor for measuring the water content of soil comprises a probe 1, a fiber Bragg grating 2, a soft cable type electric heating element 12, a cylinder shell inner wall 14, a cylinder shell outer wall 15 and a cylinder top 18; wherein, the inner wall 14 of the cylinder shell, the outer wall 15 of the cylinder shell and the top 18 of the cylinder form a cylinder with an opening at one end, one end of the probe 1 positioned at the central shaft of the cylinder is fixedly connected with the bottom of the top 18 of the cylinder, and the other end of the probe 1 is used as a free end and is provided with a needle tip 3; a groove 4 is formed in the inner side of the probe 1 and used for placing the optical fiber Bragg grating 2, and the optical fiber Bragg grating 2 is led out of the probe 1 through an optical fiber 5; the flexible cable type electric heating element 12 is spirally wound between the inner wall 14 of the cylinder shell and the outer wall 15 of the cylinder shell to form an interlayer and is led out through a temperature-resistant flexible wire 13.
The optical fiber 5 is connected with external equipment through a detection interface module 6, and a temperature-resistant flexible wire 13 is connected with a power adapter for external power supply through a heating interface module 7.
The open end of the cylinder is provided with a sharp corner 17 along the axial direction.
The top 18 of the cylinder is made of polyurethane heat-insulating material; the inner wall 14 of the cylinder shell adopts an aluminum shell; the outer wall 15 of the cylinder shell is made of polyurethane heat-insulating material.
The device also comprises a piston shaft 8, a piston handle 9, a return spring 10 and a piston 11; one end of a piston shaft 8 is connected with a piston handle 9, the other end of the piston shaft 8 penetrates through a hole 19 formed in the top 18 of the cylinder and extends into the cylinder to be connected with a piston 11, two ends of a return spring 10 are respectively connected and fixed with the top 18 of the cylinder and the piston 11, and a ring 20 is reserved at the circle center position of the piston 11 to allow the probe 1 to penetrate through.
The open end of the cylinder is provided with barbs 16 in the radial direction.
The piston 11 is made of polyurethane heat-insulating material; the inner wall 14 of the cylinder shell adopts an aluminum shell; the outer wall 15 of the cylinder shell is made of polyurethane heat-insulating material.
The utility model has the advantages that: the utility model can heat the soil sample in the cylinder, measure the heat conductivity coefficient by using the sensor, and determine the corresponding water content according to the relation between the soil water content and the soil heat conductivity; the utility model has simple structure, convenient measurement and low cost, and can realize the on-site on-line measurement of the moisture content of the soil; meanwhile, the optical fiber Bragg grating is adopted in the structure, so that the water content monitoring device has strong electromagnetic interference resistance and corrosion resistance and is suitable for long-term monitoring of the water content.
Drawings
FIG. 1 is a schematic view of the structure of the present invention;
FIG. 2 is a cross sectional view of the structure of the present invention;
fig. 3 is a bottom plan sectional view of the present invention;
FIG. 4 is a graph of the constant heat flux density uniform heating of the soil in the cylinder of the present invention;
fig. 5 is a first-order fitting curve graph of the central wavelength of the fiber Bragg grating of the present invention varying with temperature;
FIG. 6 is a graph showing the relationship between water content and thermal conductivity of different clays;
the reference numbers in the figures are: the device comprises a probe 1, a fiber Bragg grating 2, a needle point 3, a groove 4, an optical fiber 5, a detection interface module 6, a heating interface module 7, a piston shaft 8, a piston handle 9, a return spring 10, a piston 11, a soft cable type electric heating element 12, a temperature-resistant flexible wire 13, a cylinder shell inner wall 14, a cylinder shell outer wall 15, a barb 16, a sharp corner 17, a cylinder top 18, a hole 19 and a ring 20.
Detailed Description
The invention will be further described with reference to the following drawings and examples, but the scope of the invention is not limited thereto.
Example 1: as shown in fig. 1-6, a fiber Bragg grating sensor for measuring the water content of soil comprises a probe 1, a fiber Bragg grating 2, a flexible cable type electric heating element 12, a cylinder shell inner wall 14, a cylinder shell outer wall 15 and a cylinder top 18; wherein, the inner wall 14 of the cylinder shell, the outer wall 15 of the cylinder shell and the top 18 of the cylinder form a cylinder with an opening at one end, one end of the probe 1 positioned at the central shaft of the cylinder is fixedly connected with the bottom of the top 18 of the cylinder, and the other end of the probe 1 is used as a free end and is provided with a needle tip 3; a groove 4 is formed in the inner side of the probe 1 and used for placing the optical fiber Bragg grating 2, and the optical fiber Bragg grating 2 is led out of the probe 1 through an optical fiber 5; the flexible cable type electric heating element 12 is coiled in a sandwich layer formed between the inner wall 14 of the cylinder shell and the outer wall 15 of the cylinder shell and is led out through a temperature-resistant flexible wire 13 made of fluorine.
Further, the optical fiber 5 may be connected to an external device through the detection interface module 6, and the temperature-resistant cord 13 may be connected to an external power adapter through the heating interface module 7. Two mutually independent signal input and output channels of the sensor connected with the external equipment are led out through the detection interface module 6: an external laser source is connected with the input end of an optical fiber 5 through an FC/APC joint on a detection interface module 6, an input optical signal enters an optical fiber Bragg grating 2, the central wavelength of the grating is changed due to temperature change, the signal returns from the output end of the optical fiber 5 and is transmitted to an optical fiber demodulator for demodulation, the output end of the optical fiber 5 and the optical fiber demodulator are connected through another FC/APC joint, and the two joints are installed in the detection interface module 6. The soft cable type electric heating element 12 is led out to the heating interface module 7 through a plug on a temperature-resistant flexible wire 13, and a power supply hole is reserved on the heating interface module 7 and used for being connected with a power supply adapter for supplying power to the external power supply and supplying power to the heating part. The detection interface module 6 and the heating interface module 7 are connected with external equipment through holes reserved on the top 18 of the cylinder.
Furthermore, the open end of the cylinder can be provided with a sharp corner 17 along the axial direction, so that the cylinder is convenient to insert into soil.
Further, the top 18 of the cylinder can be made of rigid polyurethane heat insulation material, so that heat can be prevented from being longitudinally dissipated; the inner wall 14 of the cylindrical shell is made of an aluminum shell, so that heat conduction is easy; the outer wall 15 of the cylinder shell is made of polyurethane heat-insulating materials, so that heat loss can be reduced, and heating is more uniform and faster.
Further, the total length of the probe 1 can be set to be longer than the inner wall 14 and the outer wall 15 of the cylindrical shell, so that the probe can be conveniently buried in the soil.
Further, the probe 1 and the steel needle tip 3 can be arranged as an integral structure, and 304 stainless steel is adopted.
Further, a gap of 1.5mm can be reserved between the inner wall 14 of the cylinder shell and the outer wall 15 of the cylinder shell, a soft cable type electric heating element 12 with the diameter of 1.4mm can be just placed in a sandwich layer between the inner wall 14 of the cylinder shell and the outer wall 15 of the cylinder shell in a spiral shape from the bottom, the winding height of the soft cable type electric heating element can be adjusted adaptively according to experiments, and the purpose is to enable the inner space of the cylinder to be heated uniformly and stably at 360 degrees.
Example 2: as shown in fig. 1-6, a fiber Bragg grating sensor for measuring the water content of soil comprises a probe 1, a fiber Bragg grating 2, a flexible cable type electric heating element 12, a cylinder shell inner wall 14, a cylinder shell outer wall 15 and a cylinder top 18; wherein, the inner wall 14 of the cylinder shell, the outer wall 15 of the cylinder shell and the top 18 of the cylinder form a cylinder with an opening at one end, one end of the probe 1 positioned at the central shaft of the cylinder is fixedly connected with the bottom of the top 18 of the cylinder, and the other end of the probe 1 is used as a free end and is provided with a needle tip 3; a groove 4 is formed in the inner side of the probe 1 and used for placing the optical fiber Bragg grating 2, and the optical fiber Bragg grating 2 is led out of the probe 1 through an optical fiber 5; the flexible cable type electric heating element 12 is coiled in a sandwich layer formed between the inner wall 14 of the cylinder shell and the outer wall 15 of the cylinder shell and is led out through a temperature-resistant flexible wire 13 made of fluorine.
Further, the optical fiber 5 may be connected to an external device through the detection interface module 6, and the temperature-resistant cord 13 may be connected to an external power adapter through the heating interface module 7. Two mutually independent signal input and output channels of the sensor connected with the external equipment are led out through the detection interface module 6: an external laser source is connected with the input end of an optical fiber 5 through an FC/APC joint on a detection interface module 6, an input optical signal enters an optical fiber Bragg grating 2, the central wavelength of the grating is changed due to temperature change, the signal returns from the output end of the optical fiber 5 and is transmitted to an optical fiber demodulator for demodulation, the output end of the optical fiber 5 and the optical fiber demodulator are connected through another FC/APC joint, and the two joints are installed in the detection interface module 6. The soft cable type electric heating element 12 is led out to the heating interface module 7 through a plug on a temperature-resistant flexible wire 13, and a power supply hole is reserved on the heating interface module 7 and used for being connected with a power supply adapter for supplying power to the external power supply and supplying power to the heating part. The detection interface module 6 and the heating interface module 7 are connected with external equipment through holes reserved on the top 18 of the cylinder.
Further, the open end of the cylinder can be provided with a sharp corner 17 along the axial direction to facilitate the insertion into soil, and the open end of the cylinder is provided with a barb 16 along the radial direction.
Further, the device can also comprise a piston shaft 8, a piston handle 9, a return spring 10 and a piston 11; one end of a piston shaft 8 is connected with a piston handle 9, the other end of the piston shaft 8 penetrates through a hole 19 formed in the top 18 of the cylinder and extends into the cylinder to be connected with a piston 11, two ends of a return spring 10 are respectively connected and fixed with the top 18 of the cylinder and the piston 11, and a ring 20 is reserved at the circle center position of the piston 11 to allow the probe 1 to penetrate through. The tested soil in the cylinder can be conveniently taken out by pushing the piston 11 after the soil is inserted for measurement, and meanwhile, the barbs 16 arranged inside the inner wall 14 of the shell of the cylinder can prevent the piston 11 from falling out of the cylinder when the piston 11 is pushed.
Further, the piston 11 can be made of rigid polyurethane heat insulation material, so that heat can be prevented from being longitudinally dissipated; the inner wall 14 of the cylindrical shell is made of an aluminum shell, so that heat conduction is easy; the outer wall 15 of the cylinder shell is made of polyurethane heat-insulating materials, so that heat loss can be reduced, and heating is more uniform and faster.
Further, the total length of the probe 1 can be set to be longer than the inner wall 14 and the outer wall 15 of the cylindrical shell, so that the probe can be conveniently buried in the soil.
Further, the probe 1 and the steel needle tip 3 can be arranged as an integral structure, and 304 stainless steel is adopted.
Further, a gap of 1.5mm can be reserved between the inner wall 14 of the cylinder shell and the outer wall 15 of the cylinder shell, a soft cable type electric heating element 12 with the diameter of 1.4mm can be just placed in a sandwich layer between the inner wall 14 of the cylinder shell and the outer wall 15 of the cylinder shell in a spiral shape from the bottom, the winding height of the soft cable type electric heating element can be adjusted adaptively according to experiments, and the purpose is to enable the inner space of the cylinder to be heated uniformly and stably at 360 degrees.
Furthermore, a cylinder top 18 can be provided with two symmetrical circular through holes 19 with the diameter of 5mm, a cylindrical piston shaft 8 with the diameter of 4mm can penetrate through the through holes, a circular ring 20 with the diameter of 8mm is reserved at the circle center of the circular piston 11 and allows the probe 1 to penetrate through the through holes, the piston shaft 8, the probe 1 and the inner wall 14 of the cylinder shell have smooth surfaces, so that the piston shaft 8 and the circular piston 11 can slide up and down, the top of the piston shaft 8 is integrated with the piston handle 9, the bottom of the piston shaft 8 is integrated with the piston 11, the free length of the return spring 10 can be 100mm, after the piston handle 9 is pushed to enable the piston 11 to move downwards, the piston 11 can be automatically reset to the top of the heating area just by using the contraction elastic force generated by the return spring 10.
The utility model discloses a use as follows:
the sensor with the structure shown in the figures 1-3 is inserted into soil, the heating interface module is connected with a power supply, and the soil in the cylindrical inner space with the inner radius of 50mm and the height of 200mm is heated by a 360-degree uniform and constant heat source through the soft cable type electric heating element (the structure used here is the sensor structure with a piston, the winding height of the soft cable type electric heating element is 200mm, the part of the cylinder with the soft cable type electric heating element is completely inserted into the soil, and the radius of the inner wall of the cylinder is 50 mm). The heat carries out heat transfer along radial direction transmission with the surveyed soil in the drum, when drum inner space reached heat balance, the temperature was not changing in the surveyed soil, because the difference of moisture content can lead to the difference of soil coefficient of heat conductivity, will form different heat balance temperature in the soil that the moisture content is different after the heating. The difference in temperature will cause a shift in the center wavelength of the thermometric fiber grating. The corresponding temperature is detected through different wavelength offsets of the temperature measurement fiber bragg gratings, and therefore the soil moisture content is measured through a conversion formula.
And (3) analyzing a mathematical model:
the sensor is buried in the soil to be measured, the cylindrical constant temperature heating body is used as a heat source and can reach stable temperature under the heating of given voltage, the heat is uniformly distributed on the inner wall of the cylinder shell, and the heat is conducted to the inner part by constant heat. The heat conductivity coefficient of the measured medium is constant, and heat is only conducted along the radial direction. According to a second type of boundary conditions, the internal radius of the cylinder is 2 delta and the initial temperature t is0The soil in the cylinder is subjected to constant heat flux q at 360 degreescHeating was uniform (see fig. 4).
The temperature distribution t (x, τ) along the radial x-axis inside the cylinder is determined at any instant.
The thermal conductivity differential equation, initial conditions and second type boundary conditions are as follows:
t(x，0)＝t0
the solution to the equation is:
in the formula: τ is time; lambda is the thermal conductivity of the soil; alpha is the temperature conductivity coefficient of the soil; mu.sn＝βnδ, n is the root of equation β, 1, 2, 3, … … nnIs a positive increasing sequence of numbers;
is a Fourier criterion; t is t0Is the initial temperature; q. q.scIs a constant heat flux density heating from the end face into the cylinder in the x-direction;
is a dimensionless distance.
With increasing time τ, F0The larger the number, the smaller the number of stages and terms in the formula (1). When F is present0For > 0.5, the number of stages and terms become very small, only the first term is retained and the other terms are ignored, and equation (1) becomes:
thus, when F0After > 0.5, the temperature and time are linear throughout the soil in the cylinder, the rate of temperature change with time is constant and uniform throughout, and this condition is called quasi-steady state.
At quasi-steady state, the temperature at which x is 0 in the soil inside the cylinder at the probe is:
the cylinder heating surface x is as follows:
the temperature difference between the two surfaces is:
as known qcAnd δ, and Δ t is measured, the thermal conductivity can be found from equation (3):
a fiber Bragg grating is arranged at the central shaft of a heating source on the inner wall of the cylinder, and a spirally wound nichrome wire flexible cable type electric heating wire is powered by a direct current stabilized power supply and can be converted into temperature through the wavelength signal processing of the fiber Bragg grating.
The fiber grating sensor is calibrated in a laboratory in advance, a first-order fitting curve of the central wavelength changing along with the temperature is shown in figure 5, and the temperature values (R) of the soil samples measured under different wavelengths can be determined through the fitting curve2A linear correlation coefficient, the larger the value, the stronger the linear correlation of the two variables). And substituting a fitting formula according to the grating wavelength obtained in real time in the experimental site to obtain the corresponding temperature for subsequent calculation of the heat conductivity coefficient.
The temperature detected when the instrument is inserted into the soil to be measured is t (0, tau), and the current or voltage is constant, so that the heating power is a constant value. After heating, the fiber Bragg grating in the probe always feeds back the temperature t (delta, tau), and corresponding temperature difference can be obtained while measuring the actual temperature.
Although the heating is carried out by using a thin nickel-chromium alloy wire soft cable type spiral electric heating wire, the heating wire has certain heat capacity, and the soft cable type electric heating element absorbs heat before soil in the heating process. The heat actually absorbed by the soil must therefore be subtracted from the electrical power by the heat absorbed by the elements.
The soil in the cylinder is heated equally by the soft rope type electric heating element, and the temperature in the cylinderThe degree field is symmetrical to the heating source wound by the soft cable type electric heating element, and the heat flux density q iscIs calculated as:
in formula (7): u is an external power supply voltage V; i is external power supply current A; f is the cylindrical area of the soft rope type electric heating element wound, m2；Ch＝0.079J/(m2The temperature is the specific heat capacity of the cylindrical unit area wound by the soft cable type electric heating element;
is the temperature change rate of a soft rope type electric heating element (also a cylindrical heating surface).
The heat conductivity coefficient can be obtained by bringing formula (7) into formula (6):
through experimental determination, the corresponding relationship between the water content and the thermal conductivity of different clays is shown in fig. 6.
According to the test result, the heat conductivity coefficient of the soil sample is increased along with the increase of the water content, and then the increase of the heat conductivity coefficient is gradually reduced along with the increase of the water content. According to the measured and calculated heat conductivity coefficient, the corresponding water content can be found according to the experiment calibration, and the water content is consistent with the actual situation. Therefore, in practical application, the result of the test of the optical fiber soil moisture content sensor constructed based on the quasi-steady state method can meet the requirement of soil thermal property analysis.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.
Claims (7)
1. The utility model provides a measure optic fibre Bragg grating sensor of soil moisture content which characterized in that: the device comprises a probe (1), a fiber Bragg grating (2), a soft cable type electric heating element (12), a cylinder shell inner wall (14), a cylinder shell outer wall (15) and a cylinder top (18); wherein, the inner wall (14) of the cylinder shell, the outer wall (15) of the cylinder shell and the top (18) of the cylinder form a cylinder with an opening at one end, one end of the probe (1) positioned at the central shaft of the cylinder is fixedly connected with the bottom of the top (18) of the cylinder, and the other end of the probe (1) is used as a free end and is provided with a needle point (3); a groove (4) is formed in the inner side of the probe (1) and used for placing the optical fiber Bragg grating (2), and the optical fiber Bragg grating (2) is led out of the probe (1) through an optical fiber (5); the flexible cable type electric heating element (12) is spirally wound between the inner wall (14) of the cylinder shell and the outer wall (15) of the cylinder shell to form an interlayer and is led out through a temperature-resistant flexible wire (13).
2. The fiber Bragg grating sensor for measuring the water content of soil according to claim 1, wherein: the optical fiber (5) is connected with external equipment through the detection interface module (6), and the temperature-resistant flexible wire (13) is connected with a power adapter for external power supply through the heating interface module (7).
3. The fiber Bragg grating sensor for measuring the water content of soil according to claim 1, wherein: the open end of the cylinder is provided with a sharp corner (17) along the axial direction.
4. The fiber Bragg grating sensor for measuring the water content of soil according to claim 1, wherein: the top (18) of the cylinder is made of polyurethane heat-insulating material; the inner wall (14) of the cylinder shell adopts an aluminum shell; the outer wall (15) of the cylinder shell is made of polyurethane heat-insulating material.
5. The fiber Bragg grating sensor for measuring the water content of soil according to claim 1, wherein: the device also comprises a piston shaft (8), a piston handle (9), a return spring (10) and a piston (11); one end of a piston shaft (8) is connected with a piston handle (9), the other end of the piston shaft (8) penetrates through a hole (19) formed in the top (18) of the cylinder and extends into the cylinder to be connected with a piston (11), two ends of a return spring (10) are respectively connected and fixed with the top (18) of the cylinder and the piston (11), and a circular ring (20) is reserved at the circle center of the piston (11) to allow the probe (1) to penetrate through.
6. The fiber Bragg grating sensor for measuring soil moisture content according to claim 5, wherein: the open end of the cylinder is provided with barbs (16) along the radial direction.
7. The fiber Bragg grating sensor for measuring soil moisture content according to claim 5, wherein: the piston (11) is made of a polyurethane heat-insulating material; the inner wall (14) of the cylinder shell adopts an aluminum shell; the outer wall (15) of the cylinder shell is made of polyurethane heat-insulating material.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113504270A (en) * | 2021-09-06 | 2021-10-15 | 中南大学 | Cohesive soil water content tester and method based on heating vaporization method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113504270A (en) * | 2021-09-06 | 2021-10-15 | 中南大学 | Cohesive soil water content tester and method based on heating vaporization method |
| CN113504270B (en) * | 2021-09-06 | 2021-11-26 | 中南大学 | Cohesive soil water content tester and method based on heating vaporization method |
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