Application of impedance tomography to measurement of temperature distributions in hot gases

This communication describes a novel technique for measuring gas temperature distributions, based on impedance tomography. In the method, the temperature field in the hot gas is reconstructed from the temperature-induced resistance changes in a grid of thin metal wires forming the measuring device. The grid consists of 21 filaments, arranged in groups of 7 wires with an angle of 120º between the groups. The reconstruction of the temperature distribution may be reduced to the standard inversion problem of tomography. In the present case, however, the measuring mesh is relatively coarse, which leads to severe undetermination of the problem, thus rendering the commonly used inversion techniques unsuitable. Therefore, the problem is recast in the form of a Bayesian parameter estimation problem where Markov Chain Monte Carlo methods (MCMC) are applied for extracting the temperature field. The operation of the algorithm is demonstrated through an application to synthetic data infected by noise. Results are presented on the use of the method for measurement of two temperature distributions above a hot-air blower, one with a single peak and the other with two peaks lying close to each other. The reconstructed distributions agree well with the temperature readings measured with auxiliary thermocouples located at several positions in the hot gas stream. As compared to the 21-wire device based on the principle of tomography, to achieve an equal resolution with the point-wise thermocouples, an array of ca. 100 sensors would have been needed, which is more tedious to implement and operate.