Sound Radiation and Propagation of Leakage Jet through a Tube Array in Power Boilers

In this paper, a mathematical model of leakage sound propagation through a heat exchanger tubes array in boilers is established, which is based on the Twersky\´s sound scattering theory, transmission grating diffraction theory, Fabry-Perot\´s interference principle, and algebraic iteration method. The tubes array is made up of large number periodically arranged tubes immersed in air. Its acoustics transmission properties are examined experimentally and theoretically. The stopping frequency, passing frequency and its bandwidth of leakage sound through the tube arrays with different structure parameter are calculated. The definition of "deaf-band" and "audible-band" of inner tube leakage sound transmission of tube array are given. The experiments of sound propagation characteristic through tube array using electro-acoustic spectral and real air leakage spectral are studied respectively. It was tested that the "deaf band" position of electro-acoustic spectrum is consistent with the theoretical estimation. However, the width is wider than theoretical prediction. The transmission properties of leakage sound spectral is well consistent with theoretical one at low frequency, but different at high frequency. The reason is that the second sound radiation is produced by the interaction between leaking ejection fluid and tube array. The sound transmission characteristic with different rows is concluded at the same time. It offers the evidence for the orientation and location of leakage source well. As same as the phononic crystals, the tube array structure has stop effect and pass effect on leaking sound propagation. The leaking sound radiation in tube array includes leaking jet noise and the second order noise caused by the interaction between the leaking jet and tube array.