| Gas is one of the main influencing factors limiting the safe production of coal mines,and methane is the main component of gas.Therefore,the accurate detection of methane concentration is important for effective prevention and early warning of gas disasters.The current methane gas concentration detection methods are mainly electrochemical,thermal and optical,but all these methods show certain limitations in the special environment of underground coal mines such as sulfurous,oxygen-free and high dust.The acoustic resonance detection method is a new "poisoning" resistant,fast response measurement method that can effectively overcome the inherent defects of existing methane sensors due to the detection principle,and is of great significance to improve the accuracy and stability of methane concentration detection.Therefore,the acoustic resonance characteristics of methane gas are investigated in this paper,and Helmholtz-type acoustic methane sensor resonance characteristics and design principle study are presented.Therefore,this paper researched the acoustic resonance characteristics of methane gas and presented the resonance characteristics and design principle study of Helmholtz type acoustic methane sensor.The main work is as follows:(1)Based on the Helmholtz resonance principle,the basic principle of acoustic detection of methane concentration is elucidated by combining the acoustic resonance characteristics of methane gas with methane concentration detection technology,using the acoustic resonance frequency as an index for measuring the methane concentration to be measured,using the differences in acoustic resonance characteristics of different concentrations of methane gas.At the same time,a centralized parametric model is used to study the circuit method by electricacoustic analogy,and the acoustic fluctuation equation and Helmholtz resonance equation are combined on the basis of ambient temperature and pressure compensation to elaborate the intrinsic connection between acoustic resonance frequency and methane gas concentration,and finally a Helmholtz-type acoustic model for methane concentration detection is established.(2)Combining theoretical and numerical analytical algorithms,the acoustic model of methane concentration detection is concretely analyzed to obtain the influence of different environmental parameters on the acoustic resonance characteristics of methane gas.It is proposed that temperature is the main factor affecting the acoustic resonance characteristics of methane gas.The acoustic resonance characteristics of methane gas with different resonant cavity geometries are also analyzed.The results provide a theoretical basis for designing the optimum resonant cavity size and the optimal sampling frequency interval.(3)According to the acoustic resonance characteristics of methane gas,combined with the theory of homogeneous medium and the introduction of sponge as acoustic substrate,the acoustic methane concentration detection structure of acoustic wave conduit composite resonant cavity unit is designed and fabricated.Meanwhile,Lab VIEW software was developed to design the acoustic methane concentration detection software system by modular programming of the front panel user interface and the back panel program block diagram.Finally,the software and hardware design of the Helmholtz-type acoustic methane concentration sensor was completed.(4)Following the completion of hardware design and software system development,a Helmholtz-type acoustic methane sensor system was built and performance tests of the methane sensor system were carried out.The performance parameters such as sensitivity,accuracy,response time,stability and repeatability of the sensor were obtained experimentally,and the applicability and accuracy of the acoustic model for methane concentration detection were verified. |
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