Temperature Field Reconstruction Based On Acoustic Tomography

Gas temperature is one of the most important information required in furnace operating. In order to maintain furnace running safely, the furnace combustion process must be automatically controlled. By measuring the furnace temperature fields, the combustion process can be controlled in time, which ensures that the combustion presses is in optimization mode. Gas temperatures inside a modern furnace is high as 3000°F(1650°C), and contact measuring methods are not suitable due to the hot condition. Furthermore, the monitor of temperature field on-line can not be achieved by conventional thermocouple and water-cooled thermocouple.Temperature field measurement by acoustic tomography is introduced in this paper. As a new temperature measurement technology, acoustic method has many advantages such as non-contact, wide temperature range (0~1900°C), large space of measuring object (up to a few decameters), high-precision, real-time, continuous measurement, easy maintenance and so on. It will be more and more useful in industrial boiler temperature field measuring. Besides, it also can be used to monitor and adjust the temperature of a theater, sense the temperature distribution of atmosphere and ocean.In this paper, many measurement methods of temperature field in industry furnace are summarized; the principle and the development status of temperature field measurement by acoustic tomography are introduced. Exponential SVD reconstruction algorithm is describe, many influences on the temperature reconstruction precision are investigated such as the number of the acoustic sound sensors (i.e. emitters/receivers), the locations of the sensors, the division of the image area and the complex degree of temperature distribution. Two new temperature reconstruction methods, regularized exponential reconstruction algorithm, Landweber iterative exponential reconstruction algorithm are proposed. Compared with exponential SVD algorithm, new algorithms are more suitable for complex temperature field reconstruction. The bending effect of sound wave paths is an important factor that influences the precision of reconstruction of temperature field. That the straight line between transmitters and receivers is thought as sound wave paths will cause great errors, especially for temperature field whose temperature gradient is steep. This paper revise reconstruction of temperature field for better precision of reconstruction using bending wave paths calculated by solving differential equations which are derived from Fermat's theorem and the calculus of variations.These algorithms are investigated using simulation data by mathematic engineering software- MATLAB. With 8 or 16 acoustic sound emitters/receivers, four industry furnace temperature distributions, i.e. symmetrical single temperature peak model, asymmetrical single temperature peak model, symmetrical dual temperature peak model, and asymmetrical dual temperature peak model, are reconstructed by the three algorithms respectively. Reconstruction error analysis indicates that all the two new algorithms can reconstruct temperature field with better precision; and the reconstruction accuracy can be increased when we take the effect of the bending sound wave paths into account. Two-dimension temperature field reconstruction experiment is implemented in Lab, the temperature distribution reconstructed accords with the real temperature field probably.