Study On Application Of Electrical Capacitance Tomography Technique To The Measurement Of Gas-liquid Two-phase Flow

Two-phase flow system is a complex, nonlinear and dynamic system. There are interface effect and relative velocity between these two phases. That causes the difficult of measurement of two-phase flow. The parameter measurement technique of two-phase flow is an important research field.The voidage measurement of two-phase flow is very important for safety, environment protection, energy conservation and quality assurance in industry. Meanwhile, heat transfer, mass transfer and the measurement accuracy of other two-phase flow parameters depend on the flow pattern. Voidage measurement and flow pattern identification technique are two important research fields in the two-phase system.On the basis of ECT technique(Electrical Capacitance Tomography). The voidage measurement and flow pattern identification technique of gas-liquid two-phase flow were studied. Experimental results show that the developed measurement technique is effective. The main works are listed as the following:A new hybrid image reconstruction algorithm which combines Tikhonov regularization theory with SIRT(Simultaneous Reconstruction Technique) algorithm was presented. The use of Tikhonov regularization theory was to solve ill-posed problem of image reconstruction and the use of SIRT algorithm was to improve the quality of the final reconstructed image. Compared to the well-known FLBP(Filter Linear Back Projection) algorithm, the quality of reconstructed image by the new hybrid image reconstruction algorithm was improved. Experimental results show that the new hybrid image reconstruction algorithm is effective. The image reconstruction time for one image is 0.08 second when the image area is divided into 54 pixels and the iterative times of SIRT are 10.The measurement capacitance value of the adjacent pair was removed, and 54 capacitances value were used to the image reconstruction. Thus it has the following advantages: Firstly, the sensitivity distribution of 54 pairs of electrode (sensitivity distribution of the adjacent pairs is removed) is smoother than that of 66 pairs of electrode. The use of the sensitivity distribution of 54 pairs of electrode could help to improve the quality of reconstructed image. Secondly, the difference between the measurement capacitance value and the simulation capacitance value was found through investigation. And the difference between the adjacent pair of electrode ismore than others. So the removing of the adjacent pair of capacitance value could decrease the difference. Thirdly, the removing of the measurement capacitance value of adjacent pair decreases the dimension of the sensitivity distribution matrix from 66 to 54. The reduction of the dimension could help to improve the speed of image reconstruction. The ideas mentioned above are proved by the experimental results.On the basis of the new hybrid image reconstruction algorithm, some experiments of global voidage measurement of gas-liquid two-phase flow were carried out. Experimental results show that the total measurement time is less than 0.1 second and the maximum error of voidage measurement is less than 6%.On the basis of the new hybrid image reconstruction algorithm and fuzzy pattern recognition technique, a new method for flow pattern identification of gas-oil two-phase flow was proposed. The relevant parameter matrix of pattern identification was achieved through a large amount experiments. Experimental results show that the developed measurement technique is effective. The accuracy of flow pattern identification of stratified flow, annular flow, core flow and homogeneous flow is more than 95% and the time for flow pattern identification is less than 0.15 second. For plug flow, the accuracy is more than 90%.The software of real-time voidage measurement and flow pattern identification of gas-liquid two-phase flow was developed based on the new hybrid image reconstruction algorithm. Experiments show that the software is satisfactory.