A device and method for testing acoustic propagation characteristics in a heated bulk coal

Abstract

The application provides a device and method for testing sound propagation characteristics in loose coal body under temperature rise, and belongs to the technical field of acoustic characteristic analysis measurement. The device comprises a software test platform, an experimental cavity system, a data acquisition instrument, a gas preparation system, a power amplifier, a programmed temperature rise system, a gas analysis system and an intelligent humidifier. The experimental cavity system comprises an experimental cavity tube main body, an experimental cavity tube rear cover and a liquid heat preservation layer. A spraying system is arranged in the experimental cavity tube main body. The application adopts the liquid heat preservation layer to preserve the experimental cavity tube main body, so that the influence of the electrically generated magnetic action in the electric blanket on the microphone is eliminated. The device can simulate the propagation of sound waves in the environment of the temperature rise products of the loose coal body, and the environment comprises gas components, gas concentration and environmental humidity. The device can effectively measure and analyze the sound wave attenuation coefficient and sound wave flight time and other characteristics of the sound wave propagation in the temperature rise process of the loose coal body, and provides parameter support for the research on the acoustic measurement of the temperature of the loose coal body.

Description

Technical Field

[0001] This invention belongs to the field of acoustic characteristic analysis and measurement technology, and particularly relates to an analytical testing device and method for detecting the propagation path and characteristics of sound waves during the heating process of loose coal. Background Technology

[0002] Spontaneous combustion of coal in goaf areas is one of the important factors affecting mine safety production, and it seriously restricts mine safety production. Accurate detection of the temperature field of coal in goaf areas is the key to solving the problem of spontaneous combustion of coal.

[0003] Existing methods for detecting high-temperature points in goaf areas are mainly divided into contact and non-contact methods. Among them, contact temperature measurement methods such as thermocouple methods and borehole methods are greatly affected by environmental factors such as underground water accumulation, and the cost of underground borehole sampling is high, resulting in a large workload for temperature measurement. Non-contact temperature measurement methods such as remote sensing methods, magnetic methods, and spontaneous potential methods have poor signal anti-interference capabilities, resulting in low temperature measurement accuracy. These problems seriously affect the detection of high-temperature areas of spontaneous combustion in coal.

[0004] Acoustic thermometry has attracted much attention due to its advantages such as wide measurement range, large spatial capacity, real-time monitoring, and non-contact temperature measurement. The basic principle of acoustic thermometry is based on the physical relationship that the speed of sound in a medium is a single-valued function of the medium's temperature, reconstructing the temperature field in the medium based on this relationship. Currently, acoustic thermometry has been extensively studied in boilers, grain silos, and stockpiled biomass, with relatively mature temperature measurement models established and successfully applied in these fields. Loose coal remnants in goaf areas share certain similarities with stored grain and stockpiled biomass, all falling under the category of loose media. Therefore, acoustic thermometry holds great promise as a method for detecting high-temperature points in loose coal masses.

[0005] Currently, research on acoustic-based temperature measurement of loose coal is limited and remains in its early exploratory stages. For example, the fundamental acoustic characteristics of sound wave propagation during the heating process of loose coal are still unclear. The slow progress in researching the propagation characteristics of sound waves within heated loose coal significantly hinders the application of acoustic thermometry in the field of loose coal temperature measurement. The invention patent with application number 202011180700.5 is the patent technology we applied for earlier. This technology still has the following shortcomings: (1) The heating method used is electric blanket heating. When the current flows in the closed circuit, it will generate electromagnetic waves, which will cause serious interference to the signal received by the microphone; (2) The airflow is directly discharged after passing through the experimental chamber tube, and the gas composition generated by the substance during the heating process cannot be analyzed, which leads to inaccurate analysis of the results; (3) Although the sound wave transit time is mentioned, the specific calculation method of the sound wave transit time is not provided; (4) Real-time intelligent gas distribution cannot be realized, and the gas composition after distribution cannot be detected in real time; (5) The specific analysis method and analysis steps of the sound wave propagation path are not proposed; (6) The real environment (including temperature and humidity) of the sound wave in the void of loose coal body at different temperature points cannot be simulated.

[0006] The propagation of sound waves in loose coal is influenced by many factors and is quite complex. Temperature and gas composition have a significant impact on the flight time of sound waves in loose coal. Therefore, it is particularly important to clarify the propagation characteristics of sound waves during the heating process of loose coal. Summary of the Invention

[0007] The main objective of this invention is to provide a device and method for testing the sound propagation characteristics in loose coal bodies under heating conditions. This device, while completing the entire process of sound generation, emission, reception, acquisition, and analysis, can simultaneously perform real-time analysis of the gas composition generated at various temperature points during the heating process of loose coal bodies, analyze the sound wave propagation characteristics during the heating process of loose coal bodies with different oxygen concentrations, analyze the sound wave propagation characteristics in loose coal bodies with different saturated gases, and simulate the propagation characteristics of sound waves in loose coal body products (including temperature, humidity, and gas composition) at different temperature points. The propagation characteristics include sound wave attenuation coefficient and sound wave transit time. By analyzing the degree to which the attenuation coefficient of different sound source signals is affected by temperature, the optimal sound source signal suitable for sound wave thermometry can be selected. The test results can provide parameter support for research on acoustic measurement of loose coal body temperature, and have positive significance for the application of acoustic thermometry technology in loose coal bodies.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] One of the objectives of this invention is to provide a device for testing the sound propagation characteristics in loose coal under heating conditions, comprising a software testing platform, an experimental chamber system, a data acquisition instrument, and a gas preparation system. The data acquisition instrument is used to receive the sound wave signal transmitted by the experimental chamber system and upload it to the software testing platform. The gas preparation system serves as a gas source, delivering gas into the experimental chamber system.

[0010] The software testing platform is connected to the experimental chamber system via a power amplifier and is used for audio signal generation, sound wave signal reception and analysis, sound wave transit time calculation, and sound wave attenuation coefficient calculation.

[0011] The power amplifier is used to amplify the weak electrical signals generated by the software testing platform and transmit them to the experimental chamber system.

[0012] The experimental chamber system is connected to a programmed heating system, which is used to heat the loose coal filling the experimental chamber system in a liquid bath.

[0013] The experimental chamber system is also connected to a gas analysis system, which is used to perform real-time analysis of the gas composition of the gas discharged from the experimental chamber system and upload the analysis results to the software testing platform.

[0014] Furthermore, the audio signal includes sine wave signal, triangle wave signal, square wave signal, sawtooth wave signal, analog pulse signal, pseudo-random signal, and white noise signal.

[0015] Furthermore, the frequency response range of the power amplifier is 20Hz to 20kHz.

[0016] Furthermore, the experimental chamber system includes an experimental chamber tube body, an experimental chamber tube rear cover, and a liquid insulation layer. From left to right, the experimental chamber tube body contains a loudspeaker, a first microphone, a temperature and humidity sensor, and a second microphone. The first microphone, temperature and humidity sensor, and second microphone are all installed at the top inside the experimental chamber tube body. A first baffle is located to the right of the loudspeaker. An air inlet is located at the bottom of the experimental chamber tube body near the right side of the first baffle, and this air inlet is connected to a gas preparation system. A wire inlet is located on the right end face of the experimental chamber tube body, through which a high-temperature resistant wire is connected to a power amplifier. The instrument and speaker, the first microphone and the second microphone are connected to the data acquisition instrument via a low-level transmission line, and the temperature and humidity sensor is connected to the software testing platform via a data line; the experimental chamber tube rear cover and the experimental chamber tube body are detachably connected to form the experimental chamber tube, the experimental chamber tube rear cover is provided with a conical sound-absorbing sponge inside, a second baffle is provided on the left side of the conical sound-absorbing sponge, and an air vent is opened at the top of the experimental chamber tube rear cover near the right side of the second baffle, the air vent is connected to the gas analysis system; the liquid insulation layer surrounds the outside of the experimental chamber tube body and is connected to the programmed temperature rise system.

[0017] Preferably, the wire diameter of the first and second retaining meshes is 0.55 mm.

[0018] Preferably, the sampling frequencies of the first and second microphones are 51,200 Hz, and the first and second microphones are piezoelectric ceramic microphones with high temperature resistance.

[0019] Preferably, the accuracy of the temperature and humidity sensor is 0.1 °C and 0.1% RH.

[0020] Preferably, the longitudinal section of the rear cover of the experimental cavity tube is a "C" - shaped structure with a side opening. The rear cover of the experimental cavity tube is connected to the main body of the experimental cavity tube by threads and is wrapped with raw tape to ensure airtightness.

[0021] Preferably, the loudspeaker and the power amplifier are connected by a phono connector.

[0022] Preferably, three Y - shaped brackets are arranged at the bottom of the main body of the experimental cavity tube. The three Y - shaped brackets support the main body of the experimental cavity tube at equal intervals, and the Y - shaped brackets are wrapped with soft rubber.

[0023] Furthermore, the programmed temperature - rising system includes a temperature controller, a temperature - rising liquid tank, and a liquid circulation pump. The temperature controller is used to adjust the temperature of the liquid medium in the temperature - rising liquid tank. The side wall of the temperature - rising liquid tank is provided with a liquid outlet pipe and a return pipe. The liquid outlet pipe is connected to the liquid inlet end arranged at the top right end of the liquid insulation layer, and the return pipe is connected to the liquid outlet end arranged at the bottom right end of the liquid insulation layer. The liquid circulation pump is arranged on the liquid outlet pipe.

[0024] Preferably, a valve switch is further arranged on the liquid outlet pipe.

[0025] Preferably, the length of the liquid inlet end on the liquid insulation layer is 6 cm, the length of the liquid outlet end is 6 cm, and a small hole with a diameter of 0.5 cm is left on the left end face of the liquid insulation layer to allow a high - temperature - resistant wire connecting the power amplifier and the loudspeaker to pass through.

[0026] Preferably, the boiling point of the liquid medium in the temperature - rising liquid tank is 100 - 300 °C, and the accuracy of the temperature controller is 0.1 °C.

[0027] Furthermore, the gas preparation system includes a gas storage tank and a dynamic gas mixer. The gas storage tank has an inlet pipe and an outlet pipe on its side wall. The dynamic gas mixer has a first standard gas inlet, a second standard gas inlet, a third standard gas inlet, a fourth standard gas inlet, a mixed gas outlet, and a waste gas outlet. The gas storage tank is connected to the mixed gas outlet via the inlet pipe, and the inlet port is connected to the gas storage tank via the outlet pipe. The first standard gas inlet, the second standard gas inlet, the third standard gas inlet, and the fourth standard gas inlet are respectively connected to… The gas cylinders are connected to a first, second, third, and fourth gas cylinder via PTFE tubing. Each of the first, second, third, and fourth gas cylinders is equipped with a pressure reducing valve. The gas stored in the first, second, third, and fourth gas cylinders enters the dynamic gas mixer through the first, second, third, and fourth standard gas inlets, is mixed in proportion, and then sent to the gas storage tank through the mixed gas outlet. The waste gas generated in the dynamic gas mixer is discharged through the waste gas outlet.

[0028] Preferably, a gas rotor flow meter is provided on the gas outlet pipe.

[0029] More preferably, the gas rotor flow meter has an accuracy class of 2.5 and a measurement range of 0.1-1 L / min.

[0030] Preferably, the exhaust pipe and the intake pipe are made of polytetrafluoroethylene (PTFE).

[0031] Furthermore, the gas analysis system includes a gas chromatograph and a gas-liquid separator. The gas-liquid separator adopts a three-way pipe structure and is filled with granular dry silica gel. The inlet of the gas-liquid separator is connected to an outlet, one of the outlets of the gas-liquid separator is connected to the analytical gas inlet of the gas chromatograph, and the other outlet of the gas-liquid separator is directly discharged outdoors. The gas chromatograph is equipped with a chromatographic column connected to the analytical gas inlet, and has an exhaust outlet for discharging waste gas from the chromatographic column. The gas chromatograph is connected to a software testing platform through a computer connection port.

[0032] Preferably, a second switch is provided at the outlet of the gas-liquid separator connected to the analytical gas inlet, and a first switch is provided at the other outlet of the gas-liquid separator.

[0033] Furthermore, the experimental chamber is also equipped with a spray system, which consists of twelve nozzles evenly distributed inside the experimental chamber. Each nozzle is connected to a spray inlet located at the bottom of the experimental chamber via a water pipe.

[0034] Furthermore, the sound propagation characteristics testing device for loose coal body used for heating also includes an intelligent humidifier. The intelligent humidifier has a wiring hole at the bottom, through which wires connect the intelligent humidifier to the software testing platform. The intelligent humidifier has a water tank at the top, with a humidifier outlet on the water tank, and the humidifier outlet is connected to the spray inlet.

[0035] The second objective of this invention is to provide a method for testing the sound propagation characteristics in loose coal under heating conditions, which is achieved using the aforementioned device for testing the sound propagation characteristics in loose coal under heating conditions, specifically through the following steps:

[0036] (1) Place the loose coal of different grades into the main body of the experimental chamber and close the back cover of the experimental chamber.

[0037] (2) Open all experimental instruments, check the integrity of the equipment, and calibrate the first and second microphones with a sound calibrator.

[0038] (3) Open the air inlet and outlet of the main body of the experimental chamber, set the flow rate of the rotor flowmeter to 120 mL / min, and open the pressure reducing valve of the corresponding gas cylinder.

[0039] (4) Turn on the temperature controller, set the maximum temperature to 150℃, the heating rate to 0.1℃ / min, and turn on the liquid circulation pump;

[0040] (5) Turn on the gas chromatograph and set the sampling rate to analyze the gas components for every 1°C increase;

[0041] (6) Select a sound wave signal on the software testing platform and transmit it to the loudspeaker through the power amplifier. After the sound wave passes through the loose coal body to be tested, it is transmitted to the data acquisition instrument by the first microphone and the second microphone. Then it is transmitted to the software testing platform through the data acquisition instrument. The sound wave emission interval is 10 min / time.

[0042] (7) The temperature and humidity sensor and gas chromatograph transmit the collected data to the software testing platform;

[0043] (8) The software testing platform draws conclusions by calculating the sound wave flight time and sound wave attenuation coefficient from the collected data.

[0044] Furthermore, in step (8), the acoustic wave transit time is calculated using a cross-correlation algorithm of the received signals. The specific calculation method is as follows:

[0045] The signal received by the first microphone is x1(k) = s(k) + W1(k);

[0046] The signal received by the second microphone is x2(k) = s(kD) + W2(k);

[0047] W1 and W2 are the signals after background noise has been added, and D is the signal delay time.

[0048] The cross-correlation function between the first microphone and the second microphone is:

[0049] R x1x2 (τ)=E{x1(k)x2(k+τ)}=E{(s(k)+w1(k))(s(k-D+τ)+w2(k+τ))}

[0050] =R ss (τ-D)+R sw1 (τ-D)+R sw2 (τ)+Rw1w2(τ);

[0051] If the signal s(k) and noise W1(k) and W2(k) satisfy the uncorrelated assumption, then: R SW1 (τ-D)=0, R SW2 (τ)=0, R W1W2 (τ)=0, then we get: R x1x2 (τ)=R ss (τ-D); From the properties of autocorrelation, we obtain: |R ss (τ-D)|≤R ss (0), R ss (τ-D) reaches its maximum when τ-D=0, where τ is the time it takes for the sound wave to travel between the first and second microphones.

[0052] Furthermore, in step (8), the sound wave attenuation coefficient is calculated using an exponential equation, and the specific calculation method is as follows:

[0053] The distance from the first microphone to the loudspeaker is r1, and the distance from the second microphone to the loudspeaker is r2. The sound pressure levels at points r1 and r2 are:

[0054] In the formula, p1(f) and p2(f) are the sound pressures at the first and second microphones, respectively, in Pa; f is the sound wave frequency, in Hz;

[0055] It can be deduced that This is the final expression of the sound wave attenuation coefficient.

[0056] Furthermore, during step (6), the liquid circulation pump in step (4) stops working, and the air inlet and outlet in step (3) are closed.

[0057] Furthermore, during step (5), the second switch is turned off every five minutes and turned back on after the gas chromatograph has finished analyzing the data.

[0058] Furthermore, in step (6), the selected acoustic signal can be changed in real time as needed.

[0059] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0060] (1) The sound propagation characteristics test device for loose coal body for heating of the present invention uses a liquid insulation layer to insulate the main body of the experimental cavity tube. By continuously ventilating and supplying the loose coal body, the loose coal body is spontaneously heated on the one hand, and the effect of the electromagnetism in the electric blanket on the microphone is eliminated on the other hand. At the same time, the main body of the experimental cavity tube is insulated to prevent heat from dissipating.

[0061] (2) The sound propagation characteristics test device for loose coal body for heating of the present invention contains a gas chromatograph. While completing the entire process of sound generation, sound emission, reception, collection and analysis, it can perform real-time analysis of the products of loose coal body heating at different temperatures. It can analyze the gas composition and concentration generated during the heating process of loose coal body in real time.

[0062] (3) The sound propagation characteristics test device for loose coal body for heating of the present invention includes an intelligent dynamic gas mixing instrument and an intelligent humidifier, which can intelligently configure the gas components required at different temperature points in real time, simulate the humidity change during coal heating, and the gas components can be analyzed in real time by a gas chromatograph. The temperature and humidity sensor can measure the humidity in the experimental chamber in real time to ensure that the type, concentration and environmental humidity of the prepared gas are accurate.

[0063] (4) The present invention can simulate the sound wave flight time in loose coal products at different temperature points by cleaning the main body of the experimental chamber, injecting only the prepared gas into the main body of the experimental chamber, setting the humidity in the main body of the experimental chamber through an intelligent humidifier, and heating through a programmed heating liquid tank, thereby calculating the speed of sound wave propagation in loose coal at different temperature points.

[0064] (5) The sound propagation characteristic testing device for heating loose coal body of the present invention adopts a software testing platform that can emit a variety of sound wave waveforms, which can test the attenuation characteristics of sound waves in heating loose coal body under different sound source signals, and select the best sound source signal for propagation in loose coal body.

[0065] (6) The sound propagation characteristics test device for loose coal body for heating of the present invention contains a gas-liquid separator, which dries the gas generated by heating the loose coal body by drying silica gel to prevent the gas sample from having excessive humidity, which would damage the gas chromatograph.

[0066] (7) This invention calculates the flight time of sound waves in loose coal bodies with different grades and different saturated gases by using the cross-correlation method, and verifies it by using the attenuation coefficient, and infers the propagation path of sound waves in loose coal bodies.

[0067] (8) The sound propagation characteristic testing device for loose coal body for heating of the present invention can simulate the propagation of sound waves in the environment of the heating product of loose coal body. The environment includes gas composition, gas concentration and ambient humidity. It can effectively measure the sound wave propagation characteristics during the heating process of loose coal body. The test results can provide parameter support for the study of acoustic measurement of loose coal body temperature. It has positive significance for the study of acoustic temperature measurement technology in loose coal body. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of the overall structure of the sound propagation characteristics testing device for heating loose coal in Embodiment 1 of the present invention.

[0069] Figure 2 This is a schematic diagram of the experimental cavity system in Embodiment 1 of the present invention;

[0070] Figure 3 This is a schematic diagram of the programmed heating system in Embodiment 1 of the present invention;

[0071] Figure 4 This is a schematic diagram of the gas preparation system in Embodiment 1 of the present invention;

[0072] Figure 5 This is a schematic diagram of the gas analysis system in Embodiment 1 of the present invention;

[0073] Figure 6 This is a schematic diagram of the acoustic calibration instrument in Embodiment 1 of the present invention;

[0074] Figure 7 This is a schematic diagram of the intelligent humidifier in Embodiment 1 of the present invention;

[0075] Figure 8 This is a schematic diagram of the Y-shaped bracket in Embodiment 1 of the present invention;

[0076] Figure 9 This is a flowchart for determining the sound wave propagation path in loose coal in Test Example 2 of the present invention;

[0077] Figure 10 This is a flowchart illustrating the calculation of the sound wave propagation distance in loose coal in Test Example 3 of the present invention.

[0078] Figure labels: 1-Software testing platform, 2-Power amplifier, 3-Experimental chamber system, 4-Data acquisition instrument, 5-Programmed heating system, 6-Gas preparation system, 7-Gas analysis system, 8-Intelligent humidifier, 9-Liquid insulation layer, 10-First microphone, 11-Temperature and humidity sensor, 12-Second microphone, 13-Spray system, 14-Speaker, 15-First baffle, 16-Air inlet, 17-Sprayer inlet, 18-Second baffle, 19-Air outlet, 20-Conical sound-absorbing sponge, 21-Wire inlet, 22-Experimental chamber tube body, 23-Experimental chamber tube rear cover, 24-Temperature controller, 25-Heating liquid tank, 26-Liquid outlet pipe, 27-Liquid circulation pump, 28-Return pipe, 29-Valve switch, 30-Gas storage tank 31-Inlet pipe, 32-Outlet pipe, 33-Dynamic gas mixer, 34-First standard gas inlet, 35-Second standard gas inlet, 36-Third standard gas inlet, 37-Fourth standard gas inlet, 38-Mixed gas outlet, 39-Waste gas outlet, 40-First gas cylinder, 41-Second gas cylinder, 42-Third gas cylinder, 43-Fourth gas cylinder, 44-Gas rotor flow meter, 45-Gas-liquid separator, 46-First switch, 47-Second switch, 48-Gas chromatograph, 49-Analytical gas inlet, 50-Chromatographic column, 51-Waste gas outlet, 52-Computer connection port, 53-Acoustic calibrator, 54-Wiring hole, 55-Water tank, 56-Humidifier outlet, 57-Y-shaped bracket, 58-Liquid inlet, 59-Liquid outlet. Detailed Implementation

[0079] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0080] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this patent and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this patent. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. It should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to fixed connection or setting, detachable connection or setting, or integral connection or setting; they can refer to mechanical connection or electrical connection; they can refer to direct connection or indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0081] Example 1: A device for testing the sound propagation characteristics in loose coal under heating conditions.

[0082] The device includes a software testing platform 1, an experimental chamber system 3, a data acquisition instrument 4, and a gas preparation system 6. The data acquisition instrument 4 is used to receive the acoustic signals transmitted by the experimental chamber system 3 and upload them to the software testing platform 1. The gas preparation system 6 serves as a gas source and sends gas into the experimental chamber system 3.

[0083] The software testing platform 1 is connected to the experimental cavity system 3 via the power amplifier 2, and is used for audio signal generation, sound wave signal reception and analysis, sound wave transit time calculation, and sound wave attenuation coefficient calculation.

[0084] The power amplifier 2 is used to amplify the weak electrical signals generated by the software testing platform 1 and transmit them to the experimental chamber system 3.

[0085] The experimental chamber system 3 is connected to a programmed heating system 5, which is used to heat the loose coal filling the experimental chamber system 3 in a liquid bath.

[0086] The experimental chamber system 3 is also connected to a gas analysis system 7, which is used to perform real-time analysis of the gas composition of the gas discharged from the experimental chamber system 3 and upload the analysis results to the software testing platform 1.

[0087] Specifically, the experimental chamber system 3 includes an experimental chamber tube body 22, an experimental chamber tube rear cover 23, and a liquid insulation layer 9. Inside the experimental chamber tube body 22, from left to right, are arranged a loudspeaker 14, a first microphone 10, a temperature and humidity sensor 11, and a second microphone 12. The first microphone 10, temperature and humidity sensor 11, and second microphone 12 are all installed at the top inside the experimental chamber tube body 22. A first baffle 15 is provided to the right of the loudspeaker 14. An air inlet 16 is provided at the bottom of the experimental chamber tube body 22 near the right side of the first baffle 15. The air inlet 16 is connected to the gas preparation system 6. A wire inlet 21 is provided on the right end face of the experimental chamber tube body 22, through which a high-temperature resistant wire is connected to the power supply. A power amplifier 2 and a speaker 14 are connected. The first microphone 10 and the second microphone 12 are connected to the data acquisition instrument 4 via a low-level transmission line. The temperature and humidity sensor 11 is connected to the software testing platform 1 via a data line. The experimental chamber tube rear cover 23 and the experimental chamber tube body 22 are detachably connected to form the experimental chamber tube. The experimental chamber tube rear cover 23 is provided with a conical sound-absorbing sponge 20 inside. A second baffle 18 is provided on the left side of the conical sound-absorbing sponge 20. An air vent 19 is opened at the top of the experimental chamber tube rear cover 23 near the right side of the second baffle 18. The air vent 19 is connected to the gas analysis system 7. The liquid insulation layer 9 surrounds the outside of the experimental chamber tube body 22 and is connected to the programmed temperature rise system 5.

[0088] In this embodiment, the software testing platform 1 includes a built-in virtual experimental platform and a data analysis and processing system. The virtual experimental platform can generate various acoustic wave signals such as sine wave signals, triangular wave signals, square wave signals, sawtooth wave signals, analog pulse signals, pseudo-random signals, and white noise signals, and the amplitude and frequency of each waveform signal are adjustable. The data analysis system can perform data analysis on the collected signals. The first microphone 10 and the second microphone 12 are calibrated by an acoustic calibrator before use. The connection between the first microphone 10, the second microphone 12, and the temperature and humidity sensor 11 and the experimental chamber tube body 22 is sealed by a hot melt gun to improve the sealing performance of the experimental chamber system 3.

[0089] In this embodiment, the power amplifier 2 has a frequency response range of 20Hz to 20kHz. The wire diameter of the first baffle 15 and the second baffle 18 is 0.55mm. The sampling frequency of the first microphone 10 and the second microphone 12 is 51200Hz. The first microphone 10 and the second microphone 12 are high-temperature resistant piezoelectric ceramic microphones. The temperature and humidity sensor 11 has an accuracy of 0.1℃ and 0.1%RH. The longitudinal section of the experimental chamber tube rear cover 23 is a "U"-shaped structure with a side opening. The experimental chamber tube rear cover 23 is connected to the experimental chamber tube body 22 by threads and wrapped with Teflon tape to ensure sealing. The speaker 14 is connected to the power amplifier 2 using a lotus connector. The experimental chamber tube formed by the experimental chamber tube rear cover 23 and the experimental chamber tube body 22 is a cylindrical or regular polygonal prism tubular structure.

[0090] Specifically, the bottom of the experimental chamber tube body 22 is provided with three Y-shaped supports 57, which support the experimental chamber tube body 22 at equal intervals, and the Y-shaped supports 57 are covered with soft rubber.

[0091] Specifically, the programmed heating system 5 includes a temperature controller 24, a heating liquid tank 25, and a liquid circulation pump 27. The temperature controller 24 is used to regulate the temperature of the liquid medium in the heating liquid tank 25. The heating liquid tank 25 has an outlet pipe 26 and a return pipe 28 on its side wall. The outlet pipe 26 is connected to the inlet end 58 located at the top right end of the liquid insulation layer 9, and the return pipe 28 is connected to the outlet end 59 located at the bottom right end of the liquid insulation layer 9. The liquid circulation pump 27 is installed on the outlet pipe 26, and a valve switch 29 is also installed on the outlet pipe 26.

[0092] In this embodiment, the length of the liquid inlet end 58 on the liquid insulation layer 9 is 6cm, the length of the liquid outlet end 59 is 6cm, and a small hole with a diameter of 0.5cm is left on the left end face of the liquid insulation layer 9 to allow the high-temperature resistant wire connecting the power amplifier 2 and the speaker 14 to pass through; the boiling point of the liquid medium in the heating liquid tank 25 is 100~300℃, and the temperature controller 24 has an accuracy of 0.1℃.

[0093] Specifically, the gas preparation system 6 includes a gas storage tank 30 and a dynamic gas mixer 33. The gas storage tank 30 has an inlet pipe 31 and an outlet pipe 32 on its side wall. The dynamic gas mixer 33 has a first standard gas inlet 34, a second standard gas inlet 35, a third standard gas inlet 36, a fourth standard gas inlet 37, a mixed gas outlet 38, and a waste gas outlet 39. The gas storage tank 30 is connected to the mixed gas outlet 38 through the inlet pipe 31. The inlet port 16 is connected to the gas storage tank 30 through the outlet pipe 32. The first standard gas inlet 34, the second standard gas inlet 35, the third standard gas inlet 36, and the fourth standard gas inlet 37 are respectively connected by polytetrafluoroethylene pipes. There are a first gas cylinder 40, a second gas cylinder 41, a third gas cylinder 42, and a fourth gas cylinder 43. Each of the first gas cylinder 40, the second gas cylinder 41, the third gas cylinder 42, and the fourth gas cylinder 43 is equipped with a pressure reducing valve. The gas stored in the first gas cylinder 40, the second gas cylinder 41, the third gas cylinder 42, and the fourth gas cylinder 43 enters the dynamic gas mixer 33 through the first standard gas inlet 34, the second standard gas inlet 35, the third standard gas inlet 36, and the fourth standard gas inlet 37. After being mixed in proportion, the mixture is sent to the gas storage tank 30 through the mixed gas outlet 38. The waste gas generated in the dynamic gas mixer 33 is discharged through the waste gas outlet 39. A gas rotor flow meter 44 is installed on the outlet pipe 32.

[0094] In this embodiment, the gas rotor flow meter 44 has an accuracy class of 2.5 and a measurement range of 0.1-1 L / min. The outlet pipe 32 and the inlet pipe 31 are made of polytetrafluoroethylene (PTFE) tubing.

[0095] Specifically, the gas analysis system 7 includes a gas chromatograph 48 and a gas-liquid separator 45. The gas-liquid separator 45 adopts a three-way pipe structure and is filled with granular dry silica gel. The inlet of the gas-liquid separator 45 is connected to the gas outlet 19. One outlet of the gas-liquid separator 45 is connected to the analytical gas inlet 49 of the gas chromatograph 48, and the other outlet of the gas-liquid separator 45 is directly discharged outdoors. The gas chromatograph 48 is equipped with a chromatographic column 50 connected to the analytical gas inlet 49. The gas chromatograph 48 is equipped with a waste gas outlet 51 for the discharge of waste gas from the chromatographic column 50. The gas chromatograph 48 is connected to the software testing platform 1 through a computer connection port 52. A second switch 47 is installed on the outlet of the gas-liquid separator 45 connected to the analytical gas inlet 49, and a first switch 46 is installed on the other outlet of the gas-liquid separator 45.

[0096] In this embodiment, the granular dry silica gel in the gas-liquid separator 45 can be replaced in real time, and the two outlet gas paths of the gas-liquid separator 45 can be switched.

[0097] Specifically, the experimental chamber body 22 is also equipped with a spray system 13, which consists of twelve nozzles evenly distributed inside the experimental chamber body 22. Each nozzle is connected to a spray inlet at the bottom of the experimental chamber body 22 via a water pipe. The sound propagation characteristic testing device for heating loose coal also includes an intelligent humidifier 8. The intelligent humidifier 8 has a wiring hole 54 at its lower part. A wire is connected to the intelligent humidifier 8 and the software testing platform 1 through the wiring hole 54. The intelligent humidifier 8 has a water tank 55 at its upper part. A humidifier outlet 56 is provided on the water tank 55 and is connected to the spray inlet.

[0098] In this embodiment, the humidity of the intelligent humidifier 8 can be adjusted according to the software testing platform 1.

[0099] Example 2: A method for testing the sound propagation characteristics in loose coal mass under heating conditions.

[0100] The sound propagation characteristics test device for loose coal mass used for heating, as described in Example 1, was used to achieve this, specifically following these steps:

[0101] (1) Place the loose coal of different grades into the experimental chamber tube body 22 and close the experimental chamber cover.

[0102] (2) Open all experimental instruments, check the integrity of the equipment, and calibrate the first microphone 10 and the second microphone 12 with the sound calibrator 53.

[0103] (3) Open the air inlet 16 and air outlet 19 of the main body 22 of the experimental chamber tube, set the flow rate of the rotor flow meter to 120 mL / min, and open the pressure reducing valve of the corresponding gas cylinder.

[0104] (4) Turn on the temperature controller 24, set the maximum temperature to 150℃, the heating rate to 0.1℃ / min, and turn on the liquid circulation pump 27;

[0105] (5) Turn on the gas chromatograph and set the sampling rate to analyze the gas components for every 1°C increase;

[0106] (6) Select a sound wave signal on the software test platform 1 and transmit it to the speaker 14 through the power amplifier 2. After the sound wave passes through the loose coal body to be tested, it is transmitted to the data acquisition instrument 4 by the first microphone 10 and the second microphone 12. Then it is transmitted to the software test platform 1 through the data acquisition instrument 4. The sound wave emission interval is 10 min / time.

[0107] (7) The temperature and humidity sensor 11 and the gas chromatograph 48 transmit the collected data to the software testing platform 1;

[0108] (8) The software testing platform 1 draws a conclusion by calculating the sound wave flight time and sound wave attenuation coefficient from the collected data.

[0109] Specifically, in step (8), the acoustic wave transit time is calculated using a cross-correlation algorithm of the received signal. The specific calculation method is as follows:

[0110] The signal received by the first microphone 10 is x1(k) = s(k) + W1(k);

[0111] The signal received by the second microphone 12 is x2(k) = s(kD) + W2(k);

[0112] W1 and W2 are the signals after background noise has been added, and D is the signal delay time.

[0113] The cross-correlation function between the first microphone 10 and the second microphone 12 is:

[0114] R x1x2 (τ)=E{x1(k)x2(k+τ)}=E{(s(k)+w1(k))(s(k-D+τ)+w2(k+τ))}

[0115] =R ss (τ-D)+R sw1 (τ-D)+R sw2 (τ)+Rw1w2(τ);

[0116] If the signal s(k) and noise W1(k) and W2(k) satisfy the uncorrelated assumption, then: R SW1 (τ-D)=0, R SW2 (τ)=0, R W1W2 (τ)=0, then we get: R x1x2 (τ)=R ss (τ-D); From the properties of autocorrelation, we obtain: |R ss (τ-D)|≤R ss (0), R ss (τ-D) reaches its maximum when τ-D=0, where τ is the time it takes for the sound wave to travel between the first microphone 10 and the second microphone 12.

[0117] Specifically, in step (8), the sound wave attenuation coefficient is calculated using an exponential equation, and the specific calculation method is as follows:

[0118] The distance from the first microphone 10 to the loudspeaker 14 is r1, and the distance from the second microphone 12 to the loudspeaker 14 is r2. The sound pressure at points r1 and r2 is:

[0119] In the formula, p1(f) and p2(f) are the sound pressures at the first microphone 10 and the second microphone 12, respectively, in Pa; f is the sound wave frequency, in Hz;

[0120] It can be deduced that This is the final expression of the sound wave attenuation coefficient.

[0121] Specifically, when step (6) is performed, the liquid circulation pump 27 in step (4) stops working and the air inlet 16 and air outlet 19 in step (3) are closed; when step (5) is performed, the second switch 47 is turned off once every five minutes, and the gas chromatograph 48 is turned on again after analyzing the data.

[0122] In this embodiment, the selected acoustic signal in step (6) can be changed in real time as needed.

[0123] Test Example 1: Optimal Sound Source Signal Test for Sound Wave Propagation in Heated Loose Coal Body

[0124] In this experimental example, a single air cylinder is used, which is directly connected to a gas rotor flow meter via a pressure reducing valve on the air cylinder. The test workflow is as follows:

[0125] (1) Place the loose coal of different grades into the experimental chamber tube body 22 and close the experimental chamber tube back cover 23.

[0126] (2) Open all experimental instruments, check the integrity of the equipment, and calibrate the first microphone 10 and the second microphone 12 with the sound calibrator 53;

[0127] (3) Open the air inlet 16 and the air outlet 19, turn on the gas rotor flow meter 44 of the air cylinder, and set the air intake to 120 mL / min;

[0128] (4) Turn on the temperature controller 24, set the maximum temperature to 150℃, and the heating rate to 1℃ / min;

[0129] (5) Turn on the gas chromatograph and set the sampling rate to analyze the gas components every 5°C increase;

[0130] (6) Select a sine wave signal on the signal generator of the software test platform 1, and transmit it to the speaker 14 through the power amplifier 2. After the sound wave passes through the loose coal body to be tested, it is transmitted to the data acquisition instrument 4 by the first microphone 10 and the second microphone 12, and then transmitted to the software test platform 1 through the data acquisition instrument 4. The sound wave emission interval is 5 minutes.

[0131] (7) At the beginning of each experiment, close the air inlet 16 and the air outlet 19, and turn off the circulating liquid pump.

[0132] (8) The temperature and humidity sensor 11 transmits the collected data to the software testing platform 1;

[0133] (9) The signals received by the first microphone 10 and the second microphone 12 are transmitted to the software test platform 1, and the attenuation coefficient of the sound wave in the loose coal body at different temperatures is calculated using the attenuation formula.

[0134] (10) Change the signal on the signal generator of the software test platform 1 to triangular wave signal, square wave signal, sawtooth wave signal, analog pulse signal, pseudo-random signal, white noise signal and other acoustic wave signals in sequence, and change the amplitude and frequency of each waveform signal, and calculate the acoustic wave attenuation coefficient under this signal.

[0135] In step (10), the distance from the first microphone 10 to the loudspeaker 14 is r1, and the distance from the second microphone 12 to the loudspeaker 14 is r2. The sound pressure at points r1 and r2 is:

[0136] In the formula, p1(f) and p2(f) are the sound pressures at the first microphone 10 and the second microphone 12, respectively, in Pa; f is the sound wave frequency, in Hz;

[0137] This is the expression for the sound wave attenuation coefficient.

[0138] In step (10), the sensitivity of the attenuation coefficient of different sound source signals to temperature is tested. By finding the minimum sound wave attenuation coefficient, the optimal sound source signal type and frequency for transmission in the heated loose coal body are determined.

[0139] Test Example 2: Sound wave propagation path test in heated loose coal.

[0140] (1) After crushing the raw coal with a coal crusher, five particle size ranges (0.9-3mm, 3-5mm, 5-7mm, 7-10mm and greater than 10mm) are screened out. The screened coal samples are made into a five-grade mixed sample. The loose coal body to be tested is placed in the main body 22 of the experimental chamber tube. The removable experimental chamber tube back cover 23 is installed with wrapped raw rubber tape. The air tightness of the experimental chamber tube is tested. The places that are prone to leakage, such as the first microphone 10, the temperature and humidity sensor 11 and the second microphone 1211, are sealed with a hot melt gun.

[0141] (2) Connect the air cylinder directly to the gas rotor flow meter 44, open the pressure reducing valve of the air cylinder, and set the flow rate of the gas rotor flow meter 44 to 120 mL / min.

[0142] (3) Turn on the temperature controller 24, set the initial temperature to 30℃ and the maximum temperature to 150℃, and set the heating rate of the temperature controller 24 to 0.1℃ / min;

[0143] (4) Use the sound calibrator 53 to calibrate the first microphone 10 and the second microphone 12; set up the software test platform 1, and use the signal selected in test example 1 as the test signal for output. The first microphone 10 and the second microphone 12 convert the received signal into an electrical signal and transmit it to the software test platform 1 via the data acquisition instrument 4.

[0144] (5) The temperature and humidity measured by the temperature and humidity sensor 11 are taken as the actual temperature and humidity of the loose coal body. At this time, the signals received by the first microphone 10 and the second microphone 12 from the software test platform 1 are analyzed, and the flight time Ti of the sound wave in the loose coal body under this temperature and humidity environment is calculated.

[0145] (6) Replace the air cylinder with a nitrogen cylinder and a carbon dioxide cylinder respectively, and repeat the above experiment. If the sound wave transit time does not change, the sound wave propagates through the structure of the coal in the loose coal body. If the transit time changes, continue the experiment.

[0146] (7) The loose coal body was graded into different grades such as four-grade and three-grade, and the gas was set to air. The above experiment was repeated, and the final conclusion was drawn.

[0147] In this embodiment, the gases to be tested are a single air cylinder, a nitrogen cylinder, and a carbon dioxide cylinder.

[0148] In this embodiment, in steps (1) and (7), the three-level gradation produced is 3-5mm, 5-7mm, and 7-10mm, accounting for 25%, 50%, and 25% of the total, respectively; the four-level gradation produced is 3-5mm, 5-7mm, 7-10mm, and greater than 10mm, accounting for 25%, 25%, 25%, and 25% of the total, respectively; and the five-level gradation produced is 0.9-3mm, 3-5mm, 5-7mm, 7-10mm, and greater than 10mm, accounting for 10%, 15%, 50%, 15%, and 10% of the total, respectively.

[0149] In this embodiment, in step (5), the signals received by the first microphone 10 and the second microphone 12 are x1(k) = s(k) + W1(k) and x2(k) = s(kD) + W2(k), respectively, where W1 and W2 are the signals after background noise is mixed in, and D is the signal delay time.

[0150] The cross-correlation function between the first microphone 10 and the second microphone 12 is:

[0151] R x1x2 (τ)=E{x1(k)x2(k+τ)}=E{(s(k)+w1(k))(s(k-D+τ)+w2(k+τ))}

[0152] =Rss (τ-D)+R sw1 (τ-D)+R sw2 (τ)+Rw1w2(τ);

[0153] If the signal s(k) and noise W1(k) and W2(k) satisfy the uncorrelated assumption, then: R SW1 (τ-D)=0, R SW2 (τ)=0, R W1W2 (τ)=0, then we get: R x1x2 (τ)=R ss (τ-D);

[0154] Based on the properties of autocorrelation, we obtain: |R ss (τ-D)|≤R ss (0), R ss (τ-D) reaches its maximum when τ-D=0, where τ is the time it takes for the sound wave to travel between the two microphones. Data is collected three times at each sampling point, and the average of the three data is used as the experimental data.

[0155] In step (1), after the loose coal mixture is loaded into the main body 22 of the experimental chamber, the packing shape of the loose coal is not changed. The gas environment is changed for testing while maintaining the same packing shape.

[0156] In step (5), when collecting experimental data, the liquid circulation pump 27 and the gas rotor flow meter 44 are turned off to reduce the influence of the external environment on the sound collection.

[0157] Throughout the entire process described above, the morphology of the loose coal mass remains unchanged; only the gas composition within the voids of the loose coal mass is altered. By calculating the flight time of sound waves in the loose coal mass, the propagation characteristics and main paths of sound waves in the heated loose coal mass are analyzed. The analysis method follows... Figure 9 The judgment process is carried out.

[0158] Test Example 3: Test of the propagation path length of sound waves in heated loose coal.

[0159] When the propagation path of the sound wave in the loose coal mass is determined to be propagation through the coal structure in Test Example 1, its propagation length is the length between the two microphones; when the propagation path of the sound wave in the loose coal mass is determined to be propagation through the voids in the loose coal mass, its propagation path length is calculated as follows: Figure 10 As shown.

[0160] (1) Place the loose coal body with four grades (3-5mm, 5-7mm, 7-10mm and greater than 10mm accounting for 25%, 25%, 25%, and 25% of the total, respectively) into the main body 22 of the experimental chamber tube, close the removable experimental chamber tube rear cover 23, and test the air tightness of the experimental chamber tube. Use a hot melt gun to seal the locations prone to leakage, such as the first microphone 10, the temperature and humidity sensor 11, and the second microphone 12.

[0161] (2) Connect the air cylinder directly to the gas rotor flow meter 44 and set the flow rate of the gas rotor flow meter 44 to 20 mL / min. The gas passing through the experimental chamber tube passes through the gas-liquid separator 45 and then reaches the gas chromatograph 48. The gas chromatograph 48 transmits the analyzed gas data to the software test platform 1.

[0162] (3) Turn on the temperature controller 24, set the initial temperature to 30℃ and the maximum temperature to 150℃, and set the heating rate of the temperature controller 24 to 0.1℃ / min;

[0163] (4) Use the sound calibrator 53 to calibrate the first microphone 10 and the second microphone 12; set up the software test platform 1 to emit the sound source signal selected in the above test example 1; the first microphone 10 and the second microphone 12 convert the received signal into an electrical signal and transmit it to the software test platform 1 via the data acquisition instrument 4.

[0164] (5) Using the data from temperature and humidity sensor 11 as the temperature of the coal and the humidity at different temperature points, the cross-correlation method was used to analyze the sound wave transit time T at different temperature points. 1i The speed of sound wave propagation in the experimental cavity is V. 1i The gas composition obtained by heating the loose coal body at this time was obtained by gas chromatography-mass spectrometry 48.

[0165] (6) Clean the coal in the experimental chamber body 22, configure the gas composition at different temperature points obtained by the gas chromatograph 48 during the coal heating process through the dynamic gas distribution instrument 33, and set the humidity of the intelligent humidifier 8 through the software test platform 1 to simulate the gas composition, concentration and humidity environment at different temperature points during the heating process of loose coal.

[0166] (7) Using 1℃ as the unit, the dynamic gas mixing instrument 33 simulates the gas composition at different temperature points and transmits it to the air inlet 16 through the gas storage tank 30. The accuracy of the mixed gas is analyzed by the gas chromatograph 48. When the gas fills the entire experimental chamber, the air outlet 19 is closed.

[0167] (8) The gas is heated to a specific temperature by the liquid insulation layer 9, and the signal selected in the above test example 1 is used as the sound source signal. The cross-correlation method is used to measure the transit time of the sound wave in the gas at different temperature points.

[0168] (9) Taking the distance between the first microphone 10 and the second microphone 12 as L, and the flight time at different temperature points as T. 2i Based on physical formulas, calculate the velocity V of the sound wave in the gas of the experimental chamber at different temperature points. 2i ;

[0169] (10) When sound waves propagate through the gas in the pores of loose coal, V 1i =V 2i L can be calculated by considering the relationship between time, speed, and distance. 真 =T 2i ·V 1i Ltrue is the actual path length of the sound wave as it propagates in the loose coal body.

[0170] During the above experiment, after the intelligent humidifier 8 is used, the program heating system 5 should be started to heat and dry the experimental chamber.

[0171] Finally, it should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. The embodiments listed in this invention are not intended to limit the invention, and any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A device for testing the sound propagation characteristics in heated loose coal, comprising a software testing platform, an experimental chamber system, a data acquisition instrument, and a gas preparation system, wherein the data acquisition instrument receives the sound wave signal transmitted by the experimental chamber system and uploads it to the software testing platform, and the gas preparation system serves as a gas source, delivering gas into the experimental chamber system; characterized in that: The software testing platform is connected to the experimental chamber system via a power amplifier; The experimental chamber system is also connected to a programmed temperature rise system, a gas analysis system, a spray system, and an intelligent humidifier; The programmed heating system is a liquid bath heating system, used to programmatically control the temperature of the loose coal filling the experimental chamber system. The gas analysis system is used to perform real-time composition analysis on the gas discharged from the experimental chamber system and upload the analysis results to the software testing platform. The spray system is installed inside the experimental chamber system, and the intelligent humidifier is connected to the spray system to regulate the humidity inside the experimental chamber system. The software testing platform is configured to: collaboratively control the programmed heating system, gas preparation system, gas analysis system, intelligent humidifier and spray system, so as to simulate the coupled environment of temperature, humidity and gas concentration in the pores of loose coal at different temperature points during the heating process of loose coal in the experimental chamber system, and analyze the propagation characteristics of sound waves in this coupled environment. The test of the actual propagation path length of sound waves in heated loose coal includes the following steps: Loose coal of four grades (3-5mm, 5-7mm, 7-10mm, and greater than 10mm) accounting for 25%, 25%, 25%, and 25% of the total, respectively, was placed into the main body of the experimental chamber tube. The removable rear cover of the experimental chamber tube was closed, and the airtightness of the experimental chamber tube was tested. The locations prone to leakage, such as the installation locations of the first microphone, temperature and humidity sensor, and second microphone, were sealed with a hot melt gun. The air cylinder is directly connected to the gas rotor flow meter, and the flow rate of the gas rotor flow meter is set to 20 mL / min. The gas passing through the experimental chamber tube passes through the gas-liquid separator and then reaches the gas chromatograph. The gas chromatograph transmits the analyzed gas data to the software testing platform. Turn on the temperature controller, set the initial temperature to 30℃ and the maximum temperature to 150℃, and set the temperature controller's heating rate to 0.1℃ / min; The first and second microphones are calibrated using an acoustic calibrator; a software test platform is set up to emit sound source signals; the first and second microphones convert the received signals into electrical signals and transmit them to the software test platform via a data acquisition device. Using data collected by temperature and humidity sensors as the temperature of the coal and the humidity at different temperature points, the cross-correlation method was used to analyze the sound wave transit time T at different temperature points. 1i The speed of sound wave propagation in the experimental cavity is V. 1i The gas composition obtained by heating the loose coal body at this time was obtained by gas chromatography analysis. The coal in the main body of the experimental chamber was cleaned, and the gas composition at different temperature points obtained by the gas chromatograph during the coal heating process was configured by the dynamic gas mixing instrument. At the same time, the humidity of the intelligent humidifier was set by the software testing platform to simulate the gas composition, concentration and humidity environment at different temperature points during the heating process of loose coal. The dynamic gas mixing instrument simulates the gas composition at different temperature points in units of 1℃, and transmits the gas to the inlet through the gas storage tank. The accuracy of the mixed gas is analyzed by a gas chromatograph. When the gas fills the entire experimental chamber, the outlet is closed. The cross-correlation method was used to measure the transit time of sound waves in a gas at different temperature points. Let L be the distance between the first and second microphones, and T be the time of flight at different temperature points. 2i Based on physical formulas, calculate the velocity V of the sound wave in the gas of the experimental chamber at different temperature points. 2i ; When sound waves propagate through the gas in the pores of loose coal, V 1i =V 2i L can be calculated by considering the relationship between time, speed, and distance. 真 =T 2i ·V 1i Ltrue is the actual path length of the sound wave as it propagates in the loose coal body.

2. The device for testing the sound propagation characteristics in loose coal mass for heating according to claim 1, characterized in that: The experimental chamber system includes an experimental chamber tube body, an experimental chamber tube rear cover, and a liquid insulation layer. Inside the experimental chamber tube body, from left to right, are arranged a loudspeaker, a first microphone, a temperature and humidity sensor, and a second microphone. The first microphone, temperature and humidity sensor, and second microphone are all installed at the top inside the experimental chamber tube body. A first baffle is located to the right of the loudspeaker. An air inlet is located at the bottom of the experimental chamber tube body near the right side of the first baffle, and this air inlet is connected to a gas preparation system. A wire inlet is located on the right end face of the experimental chamber tube body, through which a high-temperature resistant wire connects to a power amplifier and the loudspeaker. The first microphone and the second microphone are connected to a digital amplifier via a low-level transmission line. The temperature and humidity sensor is connected to the data acquisition instrument via a data cable and then to the software testing platform. The experimental chamber tube's rear cover and main body are detachably connected to form the experimental chamber tube. The rear cover of the experimental chamber tube contains a conical sound-absorbing sponge, and a second baffle is located on the left side of the conical sound-absorbing sponge. An air vent is located on the top of the rear cover of the experimental chamber tube near the right side of the second baffle, and the air vent is connected to a gas analysis system. The liquid insulation layer surrounds the outside of the main body of the experimental chamber tube and is connected to a programmed temperature rise system. Three Y-shaped supports are located at the bottom of the main body of the experimental chamber tube, and the three Y-shaped supports are equally spaced to support the main body of the experimental chamber tube. The Y-shaped supports are covered with soft rubber.

3. The device for testing the sound propagation characteristics in loose coal mass under heating according to claim 2, characterized in that: The programmed heating system includes a temperature controller, a heating liquid tank, and a liquid circulation pump. The temperature controller is used to regulate the temperature of the liquid medium in the heating liquid tank. The side wall of the heating liquid tank is provided with an outlet pipe and a return pipe. The outlet pipe is connected to the inlet end located at the top right end of the liquid insulation layer, and the return pipe is connected to the outlet end located at the bottom right end of the liquid insulation layer. The liquid circulation pump is installed on the outlet pipe. A valve switch is also provided on the outlet pipe. The boiling point of the liquid medium in the heating liquid tank is 100-300℃.

4. The device for testing the sound propagation characteristics in loose coal mass for heating according to claim 3, characterized in that: The gas preparation system includes a gas storage tank and a dynamic gas mixer. The gas storage tank has an inlet pipe and an outlet pipe on its side wall. The dynamic gas mixer has a first standard gas inlet, a second standard gas inlet, a third standard gas inlet, a fourth standard gas inlet, a mixed gas outlet, and a waste gas outlet. The gas storage tank is connected to the mixed gas outlet via the inlet pipe, and the inlet port is connected to the gas storage tank via the outlet pipe. The first standard gas inlet, the second standard gas inlet, the third standard gas inlet, and the fourth standard gas inlet are each connected to a first standard gas outlet via a polytetrafluoroethylene (PTFE) pipe. The first, second, third, and fourth gas cylinders are all equipped with pressure reducing valves. The gas stored in the first, second, third, and fourth gas cylinders enters the dynamic gas mixer through the first, second, third, and fourth standard gas inlets, is mixed in proportion, and then sent to the gas storage tank through the mixed gas outlet. The waste gas generated in the dynamic gas mixer is discharged through the waste gas outlet. A gas rotor flow meter is installed on the outlet pipe.

5. The device for testing the sound propagation characteristics in loose coal mass for heating according to claim 4, characterized in that: Place The gas analysis system includes a gas chromatograph and a gas-liquid separator. The gas-liquid separator adopts a three-way pipe structure and is filled with granular dried silica gel. The inlet of the gas-liquid separator is connected to an outlet. One outlet of the gas-liquid separator is connected to the analytical gas inlet of the gas chromatograph, and the other outlet of the gas-liquid separator is directly discharged outdoors. The gas chromatograph contains a chromatographic column connected to the analytical gas inlet and has an exhaust outlet for discharging waste gas from the chromatographic column. The gas chromatograph is connected to a software testing platform via a computer connection port. A second switch is installed on the outlet of the gas-liquid separator connected to the analytical gas inlet, and a first switch is installed on the other outlet of the gas-liquid separator.

6. The device for testing the sound propagation characteristics in loose coal mass under heating according to claim 1, characterized in that: The experimental chamber is also equipped with a spray system, which consists of twelve nozzles evenly distributed inside the experimental chamber. Each nozzle is connected to a spray inlet located at the bottom of the experimental chamber via a water pipe.

7. The device for testing the sound propagation characteristics in loose coal mass under heating according to claim 6, characterized in that: It also includes a smart humidifier. The smart humidifier has a wiring hole at the bottom, through which wires connect the smart humidifier to the software testing platform. The smart humidifier has a water tank at the top, with a humidifier outlet on the water tank, which is connected to the spray inlet.

8. A method for testing the sound propagation characteristics in loose coal mass under heating, characterized in that, This is achieved using the sound propagation characteristics testing device for loose coal mass under heating as described in claim 1, specifically following these steps: (1) Place the loose coal of different grades into the main body of the experimental chamber and close the back cover of the experimental chamber. (2) Open all experimental instruments, check the integrity of the equipment, and calibrate the first and second microphones with a sound calibrator. (3) Open the air inlet and outlet of the main body of the experimental chamber, set the flow rate of the rotor flowmeter to 120 mL / min, and open the pressure reducing valve of the corresponding gas cylinder. (4) Turn on the temperature controller, set the maximum temperature to 150℃, the heating rate to 0.1℃ / min, and turn on the liquid circulation pump; (5) Turn on the gas chromatograph and set the sampling rate to analyze the gas components for every 1°C increase; (6) Select a sound wave signal on the software testing platform and transmit it to the loudspeaker through the power amplifier. After the sound wave passes through the loose coal body to be tested, it is transmitted to the data acquisition instrument by the first microphone and the second microphone. Then it is transmitted to the software testing platform through the data acquisition instrument. The sound wave emission interval is 10 min / time. (7) The temperature and humidity sensor and gas chromatograph transmit the collected data to the software testing platform; (8) The software testing platform calculates the sound wave transit time and sound wave attenuation coefficient by analyzing the collected data and draws conclusions. When step (6) is performed, the liquid circulation pump in step (4) stops working, and the air inlet and outlet in step (3) are closed; when step (5) is performed, the second switch is turned off once every five minutes, and the gas chromatograph is turned on again after analyzing the data.

9. The method for testing the sound propagation characteristics in loose coal mass under heating according to claim 8, characterized in that, In step (8), the acoustic wave transit time is calculated using a cross-correlation algorithm of the received signals. The specific calculation method is as follows: The signal received by the first microphone is x1(k) = s(k) + W1(k); The signal received by the second microphone is x2(k) = s(kD) + W2(k); W1 and W2 are background noise signals, and D is the signal delay time; The cross-correlation function between the first microphone and the second microphone is: If the signal s(k) and noise W1(k) and W2(k) satisfy the uncorrelated assumption, then: , , =0, then we get: From the properties of autocorrelation, we obtain: , exist At that time, the maximum was achieved. The time it takes for a sound wave to travel between the first and second microphones.

10. The method for testing the sound propagation characteristics in loose coal mass under heating according to claim 9, characterized in that, In step (8), the sound wave attenuation coefficient is calculated using an exponential equation, and the specific calculation method is as follows: The distance from the first microphone to the loudspeaker is r1, and the distance from the second microphone to the loudspeaker is r2. The sound pressure levels at points r1 and r2 are: In the formula, p1(f) and p2(f) are the sound pressures at the first and second microphones, respectively, in Pa. f is the sound wave frequency, measured in Hz; It can be deduced that This is the final expression of the sound wave attenuation coefficient.

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