Acoustic Behavior Of Steam Leakage From Boiler Tubes

The accident of "four-tube" crack in boiler has always been one of the major problems in power plant, which baffles the unit operation safely and economically. At present, the detection using acoustic method is one of the most potential technologies in early leaking stage in boiler. However, there is lack of knowledge of spectral analysis and directionality characteristic of leakage sound radiation, lack of the sound propagation characteristic under the condition of water wall boundary, tube array of heat exchanger, and temperature field in furnace. The technology of acoustic detection was embarrassed without enough acoustic knowledge as diagnostic dependence. Therefore, it is important for academic research and engineering application to study the transmission behavior and property of leaking sound in boiler tubes.In this paper, the turbulence flowing law of leakage jet in isolated tube and physical production mechanism of jet noise are studied. Experiment test of frequency characteristic of leakage jet has been done. The relationship between leakage sound radiation and pressure in tube and leakage caliber are concluded. Based on the principle of piston oscillation, a mathematical model of tube leakage sound radiation is constructed. The directionality characteristic of leakage sound radiation in far sound field is concluded and proved by the experiment test of the electroacoustic signal and real leakage signal respectively.Based on the Bloch's theory and reflection gratings theory, a mathematical model of water wall tube array is established. The sound field distribution from leakage on the surface of water wall to inner furnace is calculated by image theory and the mathematical model of isolated tube leakage sound radiation. The influence of water wall boundary around furnace on sound field distribution and the modal frequency of standing wave are analyzed. The numerical calculation of sound field distribution of low frequency modal is done by the FEM software ANSYS.Based on Twersky's sound scattering theory, transmission grating diffraction theory, Fabry-Perot's interference principle, and algebraic iteration method, a mathematical model of leakage sound propagation through the heat exchanger tube array is established. The cutoff frequency, pass frequency and bandwidth of leakage sound through different structure parameter heat exchanger tube array are calculated. The definition of "deaf-band" and "audible-band" of inner tube leakage sound of tube array are given. The experiments of sound propagation characteristic through tube array using electroacoustic spectral and real air leakage spectral are studied respectively. It was tested that the "deaf band" position of...