CN110646443B - Test method for determining microwave penetration depth by utilizing multimode microwave heating equipment - Google Patents
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- 230000035515 penetration Effects 0.000 title claims abstract description 43
- 238000010438 heat treatment Methods 0.000 title claims abstract description 27
- 238000010998 test method Methods 0.000 title claims abstract description 15
- 239000011435 rock Substances 0.000 claims abstract description 102
- 239000000463 material Substances 0.000 claims abstract description 17
- 230000002093 peripheral effect Effects 0.000 claims abstract description 3
- 239000011889 copper foil Substances 0.000 claims description 7
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 6
- 230000002238 attenuated effect Effects 0.000 claims description 6
- 229920000742 Cotton Polymers 0.000 claims description 5
- 239000000919 ceramic Substances 0.000 claims description 5
- 239000000835 fiber Substances 0.000 claims description 4
- 239000012774 insulation material Substances 0.000 claims description 3
- 238000000034 method Methods 0.000 abstract description 7
- 238000005516 engineering process Methods 0.000 abstract description 6
- 238000013461 design Methods 0.000 abstract description 4
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- 238000009412 basement excavation Methods 0.000 description 2
- 238000009529 body temperature measurement Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 239000003989 dielectric material Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000013021 overheating Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
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- 238000009472 formulation Methods 0.000 description 1
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- 238000011160 research Methods 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N22/00—Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more
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Abstract
The invention discloses a test method for determining microwave penetration depth by utilizing multimode microwave heating equipment, which comprises the steps of wrapping a microwave reflecting material and a heat insulating material on the outer peripheral wall of a cylindrical rock sample, placing the rock sample in a multimode resonant cavity, feeding microwaves from one end of the rock sample, immediately measuring the temperatures of different cross sections of the rock sample after heating to set time, drawing a depth-temperature distribution curve of the rock sample, and taking the depth corresponding to the position where the temperature distribution curve tends to be gentle as the penetration depth of the microwaves according to the exponential attenuation relation of microwave energy in the microwave penetration depth; wherein, the depth refers to the distance from the temperature measuring point to the end face of one end of the microwave feed-in end of the rock sample. The method has reasonable design and simple operation, can be widely applied to the rock crushing link for estimating the action range of the microwave, and has important significance for realizing the engineering application of the microwave technology.
Description
Technical Field
The invention relates to a method for determining the penetration depth of a rock by microwaves, in particular to a test method for determining the penetration depth of microwaves by utilizing multimode microwave heating equipment.
Background
The microwave heating causes thermal stress in the rock to cause damage and even destruction of the rock, and the microwave heating has the advantages of being green, efficient, accurate, controllable and the like in the implementation process, so that the microwave heating is regarded as a rock auxiliary crushing technology with application prospect. The microwave penetration depth is an important index for delineating the broken rock range, and the determination of the microwave penetration depth plays an important guiding role in the subsequent formulation of a mechanical excavation scheme. In the engineering site of microwave-assisted mechanical rock breaking, the microwave is transmitted and then transmitted in the rock, and is attenuated continuously in the transmission process until the microwave disappears. The penetration depth of the microwave to the rock determines the weakening range of the rock, and mechanical excavation beyond the weakening range increases equipment loss and reduces working efficiency, thereby increasing construction cost and delaying construction period. The penetration depth of the microwave to the material is determined by the microwave frequency and the dielectric property of the material, and the dielectric property test of the rock material is not suitable for being popularized and used in engineering as a conventional measurement means because the requirements on experimental conditions and precision are harsh.
In addition, multimode microwave equipment is generally adopted in the related research of microwaves and rock media in a laboratory, the heating effect of the microwaves is enhanced by multiple working modes formed by continuously reflecting the microwaves in a resonant cavity, excessive damage to the rocks which is not in accordance with the actual engineering is caused, and the corresponding experimental data lack reference values for the engineering.
Therefore, how to simply and effectively measure the penetration depth of the microwave by using the existing experimental conditions has important significance for realizing the high-efficiency application of the microwave technology in the rock breaking link of the rock engineering.
Disclosure of Invention
The invention aims to provide a test method for determining the penetration depth of microwaves by using multimode microwave heating equipment, which is reasonable in design and simple in operation. The method can be widely applied to predicting the action range of the microwave in the rock crushing link, and has important significance for realizing the engineering application of the microwave technology.
In order to solve the technical problem, the following technical scheme is adopted in the application:
a test method for determining microwave penetration depth by utilizing multimode microwave heating equipment is characterized in that after a microwave reflecting material and a heat insulation material are wrapped on the outer peripheral wall of a cylindrical rock sample, the rock sample is placed in a multimode resonant cavity, microwaves are fed in from one end of the rock sample, when the rock sample is heated for a set time, the temperatures of different cross sections of the rock sample are immediately measured, a rock sample depth-temperature distribution curve is drawn, and according to the exponential attenuation relation of microwave energy in the microwave penetration depth, the depth corresponding to the position where the temperature distribution curve tends to be gentle is taken as the penetration depth of the microwaves; wherein, the depth refers to the distance from the temperature measuring point to the end face of one end of the microwave feed-in end of the rock sample.
Furthermore, the rock sample is formed by stacking a plurality of rock sheets with certain thickness, and the stacking gap is far smaller than the microwave wavelength. When the gaps between the rock slices are far smaller than the wavelength of the microwave, the air loss of the microwave propagating in the rock sample can be ignored.
Further, the microwave wavelength is more than 100 times of the stacking gap.
Furthermore, the heat-insulating layer is made of ceramic fiber cotton.
Further, the microwave reflecting layer is made of copper foil.
Further, heating the rock sample with different microwave powers, drawing a rock sample depth-temperature distribution curve under different microwave powers, and taking an average value of the corresponding penetration depths under the microwave powers as a final result.
Further, the rock sample is vertically placed in the multimode resonant cavity.
Further, the thickness of the rock slice is 2 cm.
Further, the heating time was set to 120 s.
Further, the microwave power is controlled to be 4-6 kw.
Further, the cross-sectional shape of the rock sample may be circular, square or triangular.
Principles and advantages
Microwave is an electromagnetic wave, and when the microwave encounters a dielectric material in free space, the attenuation occurs because the carried energy is absorbed by the material, and the absorption energy per unit volume of the rock material in the electromagnetic field is shown in formula 1:
P＝2πfε0ε″E2 (1)
wherein f is the frequency (Hz), ε0Is the dielectric constant of free space (8.85 x 10)-12F/m)，E2Is the square root of the electric field strength.
The temperature of the rock material is increased due to the absorption of microwave energy, and according to the law of thermodynamics, the energy required for the temperature increase of the rock in unit time is as follows:
P＝ρCpΔT/Δt (2)
where ρ is the density of the material (kg/m 3); cpIs the specific heat capacity (J/(kg K)) of the material; the delta T is the temperature difference (k) of the material, and the delta T is T2-T1; Δ t is a time difference(s) from an initial value, and t is t2-t 1.
The microwave penetration depth is defined as the depth at which the power density level decays to 1/e of its surface value as the microwaves propagate in the dielectric material. For rock media, whose loss factor is much smaller than the dielectric constant, the microwave penetration depth can be calculated as follows:
wherein z is the microwave penetration depth (m), λ0Is the wavelength (m) of the appropriate frequency, ε 'is the dielectric constant of the rock, ε' is the loss factor of the rock.
In rock material exposed to microwaves in free space, the electromagnetic energy within the penetration depth of the microwaves drops exponentially:
where P (z) is the power density at the z depth, P0Is the incident power density, z0Is the depth at which the power density level decays to 1/e of its surface value.
Wherein, the formulas (1) and (2) show that the microwave energy and the heat energy have a corresponding relationship, and the microwave energy absorbed by the rock can be represented by the temperature of the rock after microwave heating; formula (3) shows that the microwave penetration depth is determined with energy as a defining criterion and is independent of microwave power; equation (4) shows that the microwave energy decays exponentially within the microwave penetration depth.
In summary, the penetration depth of the microwave to the rock material can be determined according to the temperature distribution characteristics inside the rock material after microwave heating, and because the microwave penetration depth is exponentially attenuated, the temperature corresponding to the penetration depth of the microwave has an inflection point.
In addition, the microwave reflecting material is wrapped outside the rock sample, so that the sample can be prevented from absorbing the reflected microwaves in the resonant cavity, the problem that the reflected microwaves are heated for multiple times when the sample is directly placed in the microwave resonant cavity to cause inconsistency with engineering practice is avoided, the practical use scene of the microwaves can be simulated in the multimode resonant cavity, and the obtained experimental data has higher engineering reference value.
Secondly, because the microwave penetration depth is determined by taking energy as a defining standard and is irrelevant to the microwave power, and the microwave energy is exponentially attenuated in the microwave penetration depth, the microwave energy is exponentially attenuated in the microwave penetration depth under different microwave powers, namely the attenuation trends are consistent, so that the rock samples are heated under different microwave powers, and the depth-temperature distribution curves of the rock samples under different microwave powers are drawn, so that the positions of temperature inflection points can be found more intuitively and accurately, and the precision of the obtained microwave penetration depth is improved.
The beneficial effects that this application utilizes the inside temperature distribution characteristic of rock to confirm the microwave penetration depth are reasonable in design, and easy operation has avoided the test to rock dielectric property, therefore this kind of method is fit for promoting and using in the engineering, and high efficiency to realizing the microwave technology in the engineering is used and is had the significance.
Drawings
FIG. 1 pretreatment of a rock sample prior to heating;
FIG. 2 heating a rock sample within a multimode resonant cavity;
FIG. 3 temperature profile of the interior of the rock;
in the figure: 1-a core; 2-rock flakes; 3-ceramic cellucotton; 4-copper foil; 5-a multi-mode resonant cavity; 6-a microwave antenna; 7-reflecting the microwave; 8-microwave penetration depth.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A test method for determining microwave penetration depth by utilizing multimode microwave heating equipment is characterized in that the penetration depth of microwave to rock is determined by utilizing the multimode microwave heating equipment, firstly, the propagation characteristic of the microwave in free space is simulated in a multimode resonant cavity, and a rock sample is subjected to the following treatment before being heated: processing the core into a plurality of cylindrical samples and stacking the cylindrical samples into a long cylindrical rock sample, wherein in order to neglect the energy loss of microwaves when the microwaves propagate in gaps of the cylindrical samples, the gaps are far smaller than the wavelength of the microwaves by 12.2 cm; meanwhile, in order to simulate the thermal action of microwaves in an engineering scene, the curved surface of a rock sample is wrapped with copper foil before a microwave experiment so as to prevent the microwaves from overheating the rock, and in order to ensure the accuracy of temperature measurement data, heat insulation cotton needs to be wrapped. Then placing the treated rock sample right below an antenna in the multimode resonant cavity, and carrying out microwave heating under different powers; and after heating, respectively measuring the temperature of the cylindrical sample to obtain a depth-temperature distribution curve in the rock sample. And obtaining the penetration depth of the microwave to the rock sample according to the property that the rock temperature in the microwave penetration depth is attenuated according to an exponential mode and the temperature distribution is independent of the microwave power.
The depth refers to the distance from a temperature measuring point to the end face of the microwave feed-in end of the rock sample, namely the distance from the cross section of the rock sample to the end face of the microwave feed-in end of the rock sample.
It will be appreciated that the cross-sectional shape of the rock specimen may be circular, square, triangular or any other shape. In practical applications, the rock sample may be placed vertically directly in a multimode cavity, with a microwave antenna in the multimode cavity feeding microwaves from the top of the rock sample.
The method has reasonable design and simple operation, can be widely applied to the rock crushing link for estimating the action range of the microwave, and has important significance for realizing the engineering application of the microwave technology.
The present invention will be further described with reference to specific examples.
A test method for determining microwave penetration depth by utilizing multimode microwave heating equipment comprises the following steps:
and 2, stacking 20 rock slices in sequence to form a long cylindrical rock sample, sequentially wrapping the curved surface of the rock sample by using ceramic fiber cotton 3 and copper foil 4, and then placing the processed sample right below a microwave antenna 6 in a multimode resonant cavity 5 for microwave heating under different powers. The copper foil is wrapped to avoid overheating of the rock sample by microwave 7 reflected in the cavity, and the ceramic fiber cotton is wrapped to ensure the accuracy of the next temperature measurement link;
and 3, as shown in figure 2, respectively heating the processed rock sample for 120s under microwave power of 4, 5 and 6kw, then sequentially measuring the temperature of the cylindrical sample by using a handheld infrared temperature measuring gun, drawing a temperature distribution curve of the rock sample, and taking the position where the temperature distribution curve tends to be flat under different power as the penetration depth 8 of the microwave. It is noted that the temperature of the bottom region of the rock sample is high (dashed box in fig. 3) due to the reflection of the microwave as it propagates to the bottom of the cavity, and the corresponding data lacks practical significance.
And 4, performing 3 times of experiments on the same rock, wherein in order to prevent electric sparks in the experiment process, the copper foil needs to be replaced in each experiment, and the average value of the 3 times of experiment results is taken as the microwave penetration depth of the target rock.
The above examples are merely illustrative for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. Nor is it intended to be exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.
Claims (7)
1. A test method for determining microwave penetration depth by utilizing multimode microwave heating equipment is characterized in that a rock sample is placed in a multimode resonant cavity after a microwave reflecting material and a heat insulation material are wrapped on the outer peripheral wall of a cylindrical rock sample, microwaves are fed in from one end of the rock sample, when the rock sample is heated to set time, the temperatures of different cross sections of the rock sample are immediately measured, a rock sample depth-temperature distribution curve is drawn, and according to the relationship that microwave energy is exponentially attenuated in the microwave penetration depth, the depth corresponding to the position where the temperature distribution curve tends to be gentle is taken as the penetration depth of the microwaves; wherein, the depth refers to the distance from a temperature measuring point to the end face of one microwave feed-in end of the rock sample;
heating the rock sample with different microwave powers, drawing a rock sample depth-temperature distribution curve under different microwave powers, and taking the average value of the corresponding penetration depths under the microwave powers as a final result.
2. The test method of claim 1, wherein: the rock sample is formed by stacking a plurality of rock slices, and the microwave wavelength is more than 100 times of the stacking gap.
3. The test method of claim 2, wherein: the thickness of the rock slice is 2 cm.
4. The test method of claim 1, wherein: the heat insulation material is ceramic fiber cotton.
5. The test method of claim 1, wherein: the microwave reflecting material is copper foil.
6. The test method of claim 1, wherein: the rock sample is vertically placed in a multimode resonant cavity.
7. The test method of claim 1, wherein: the microwave power was controlled at 4-6kw, and the heating time was set at 120 s.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1045181A (en) * | 1990-03-27 | 1990-09-05 | 复旦大学 | Measure the microwave transmission method of penetration depth of super conducting materials |
| JPH08313456A (en) * | 1995-05-17 | 1996-11-29 | Mitsubishi Heavy Ind Ltd | Microwave resonator for high temperature |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1045181A (en) * | 1990-03-27 | 1990-09-05 | 复旦大学 | Measure the microwave transmission method of penetration depth of super conducting materials |
| JPH08313456A (en) * | 1995-05-17 | 1996-11-29 | Mitsubishi Heavy Ind Ltd | Microwave resonator for high temperature |
Non-Patent Citations (3)
| Title |
|---|
| "Investigating microwave assisted rock breakage for possible space mining applications";H. Satish等;《Mining Technology》;20061231;第115卷(第1期);第35-40页 * |
| "The influence of microwave irradiation on rocks for microwave-assisted underground excavation";Ferri Hassani等;《Journal of Rock Mechanics and Geotechnical Engineering》;20161231;第1-15页 * |
| 微波辅助机械破岩试验和理论研究进展;卢高明等;《岩土工程学报》;20160831;第38卷(第8期);第1497-1506页 * |
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