Abstract
This paper presents a sectional water fraction measurement method using electrical capacitance tomography (ECT) image. To achieve a desired measurement accuracy, an optimal threshold-search method based on fast simulated annealing (FSA) algorithm is applied for image binarization; and to guarantee the imaging time consumption, fast fixed point continuation (FFPC) iterative algorithm cooperating with the compressed sensing (CS) theory was applied to the image reconstruction. In this study, the imaging time consumption and the measurement accuracy of water fraction are used to compare the proposed method and other methods. A numerical model is established with COMSOL Multiphysics to conduct the simulative validation of the proposed method firstly and physical experiments are conducted then. The experiment results show the average relative error of water fraction is lower than 15%, where the even as low as 3.68%.
Highlights
Electrical capacitance tomography (ECT) has been widely applied to multiphase flow phase fraction detection in various industrial areas such as chemical engineering, natural gas transportation, and electric power plant [1]
A fast fixed point continuation (FFPC) iterative algorithm based on compressed sensing (CS) was applied to ECT image reconstruction, with the assistance of optimal threshold-search method based on fast simulated annealing (FSA) heuristic algorithm to binary images for water fraction measurement on gas-water two phase flow
It is obvious that the relative error of water fraction calculated by the FSA-based optimal threshold searching method is much lower than particle swarm optimization (PSO) and genetic algorithm (GA), which means FSA performs well on global solution search because of the ‘‘metropolis criteria’’; the binary images of it are more similar to the real medium distributions, and the water fraction calculation is much more accurate
Summary
Electrical capacitance tomography (ECT) has been widely applied to multiphase flow phase fraction detection in various industrial areas such as chemical engineering, natural gas transportation, and electric power plant [1]. Wang [5] proposed a new method based on ECT for voidage measurement of gas-oil two phase flow, and the image reconstruction algorithm is sample back projection. Wang et al developed an AST-ELM method [9] which directly establishes the map between measured capacitances and images This neural network based algorithm does not need a sensitivity matrix compared with traditional algorithms (such as the Landweber iterative and the linear back projection algorithm), so the ill-posed nature of ECT’s inverse system can be solved. A fast fixed point continuation (FFPC) iterative algorithm based on CS was applied to ECT image reconstruction, with the assistance of optimal threshold-search method based on fast simulated annealing (FSA) heuristic algorithm to binary images for water fraction measurement on gas-water two phase flow. The whole process of ECT inverse problem solving based on CS and FFPC is: 1) solve the sparse vector zopt in (14) by FFPC (as described in (7)-(10)); 2) calculate the gray vector gopt by according to (11)
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