Numerical Study Of Characteristics Of Acoustic Wave Propagation In Temperature Field In Furnace Based On FEM

As a new kind of effective, low cost and non-contacttemperaturemeasurementtechnical, acoustic pyrometry has a good application prospect. In abroad,the technical of acoustic pyrometry has been used to monitor the temperature ofboiler in power plant and industry. Except reliable temperature reconstructionalgorithm, there are two key factors of accurate reconstruction of temperature field infurnace, the first is to accurately obtain acoustic wave propagation time; secondly,due to wave propagation path in the temperature gradient field in furnace is bend, thetemperature reconstruction algorithm ought to take account of the refraction effect ofsound wave path. This paper is based on the theory of acoustic propagation, the directproblem that acoustic wave propagation characteristics in temperature gradientfieldswasresearched. Wave propagation time and path is obtained by the method ofnumerical simulation, which provides reference to temperature reconstruction basedon acoustic method.Based on the finite element multi-physics fields analyse software COMSOLMultiphysics and wave equation, it is established the model of acoustic wavepropagation in temperature fields. Reasonable sound source is structured to simulateand optimize reality pulse acoustic signal, the different boundary conditions wereused to study influence of actual furnace wall on acoustic propagation and acousticvelocity. Based on the acoustic pressure of source point and receiver point, thepropagation time of acoustic wave in the field was obtained using cross-correlationfunction method. It was simulated that the propagation process of a pulse acousticwave in the typical unimodal and crater-shape profile two-dimensional temperaturefield in furnace respectively, The visualization results regarding acoustic wavefrontand an acoustic wave path bending in the temperature fields are obtained, which showthat acoustic wave paths bend away from high temperature zone, and the greater thetemperature gradient, the more severely the path bends. Toverify the simulation results, the model of acoustic path equation is derivedbased on Fermat’s principle, In addition, the acoustic wave travel time on thecorresponding path is obtained by infinitesimal thought, and compared with the traveltime above-mentioned obtained by COMSOL simulation, the deviation is within1%.The reason of the deviation isthat acoustic pressure signal at emitting point movesforward. The smaller the mesh size or the higher the temperature, the more thepressure moves forward, the larger the deviation. At last, it was researched that theinfluence of model width and boundary on acoustic wave velocity, within a certainrange, the smaller the model width, the more the acoustic velocity changed; thevelocity near the boundary has a great change when the model selected hard boundaryconditions.In this paper, it was simulated and researched theoreticallybasic problems offurnace temperature measurement with acoustic method preliminary,and laid afoundation for the study of acoustic wave propagation characteristics in temperaturefield, air velocity field and combustion media coupling fields in furnace.