Research On Application Of Electrical Capacitance Tomography Technique In Thermophysics

Electrical capacitance tomography (ECT) is a process tomography (PT) based on capacitance sensing. It has the advantage of being non-intrusive, fast in response, easy to implement, low in cost, non-hazardous and capable of acquiring 2D/3D image information of process parameters. Currently, it is widely used and becoming a focus in PT research. Being a new technology, many of its foundermental aspects still require thorough investigations for complex multiphase flows, which becomes the main theme of this dissertation with main contributions as follows:The image reconstruction algorithms of ECT were reviewed in this dissertation and categorized into three groups, non-iterative algorithms, iterative algorithms and intelligent optimisation algorithms. Then a general projected-iterative scheme (GPI) for image reconstruction with electrical capacitance tomography was introduced. And a general optimized step length was derived for the scheme. Finally, a general iterative-single step image reconstruction scheme (GISS) was presented.Four different Regularization algorithms, including the Tikhonov regularization in standard form, the deep normalization method, regularized general inverse method based on smoothing constraint and the Rutishauser's method were compared in this thesis. It is concluded that all the algorithms produce similar images except the deep normalization method. The Tikhonov regularization in standard form and the regularized general inverse method based on smoothing constraint are in prior consideration.Uniform design and Least Square Support Vector Machines (LS-SVM) were applied to optimize the parameters of capacitance tomography sensors. Experiments were performed with uniform design: the spatial sensitivity distribution was taken as a performance parameter, LS-SVM was used to establish the regression model basedon the experimental results. Then, a set of optimum parameters were obtained from the regression model by the factor rotation method. Simulation results indicate that the presented method in this paper can find a set of optimal parameters for capacitance tomography sensors efficiently and effectively.A novel micro-sensor with radial screens was designed and used for flow visualization of pulsating heat pipe. The influence of three types of radial screens, the dielectric permitivity of the material between two adjacent electrodes, the distance between screen and the electrod on capacitance, are analyzed in detail.ECT was used to inspect the density variations of explosive material under pressurization. The sensor structure of internal electrodes without radial screens was used. And a linear calibration method was adopted and validated by experiments.The relationship between the measured capacitances and the permitivity of the porous media was derived by an appropriate simplification. Then a three-point calibration method was presented and used in the calibration of flame visualization in porous media. Simulation and experimental results indicate that the new method is effective.