Detection Technology And Its System Implementation For Ice-Water Two-Phase Flow Based On Impedance Tomography

In the high latitude countries and alpine region in north and west of China, disasters mainly caused by ice-water two-phase flows such as ice flood, ice jams and ice dam greatly endanger the safety of large hydraulic facilities, hydropower equipments and people’s property along the rivers. To prevent such disasters, foreign and domestic scholars did many jobs to forecast and detect conditions of ice-water two-phase flow. According to literature, researches mainly focus on field observation manually, analysis of mathematical models, indoors experiments, which have disadvantages of being lack of automatic detecting equiments for ice-water in field. This paper puts forwards a principle of ERT (Electrical Resistance Tomography) to detect the distribution and dynamic change of ice-wtaer two-phase flow. The main job is as follows: (1) ERT system to detect ice-water two-phase flow is developed, which has the tomogrphy fuction for two-phase sections and is proved by our experiments.(2) A calculating method for IPF (Ice Packing Factor) is put forward, which is based on digital image processing. The experimental results show that the errors of IPF are less than6%. Our system can be used to measure IPF of ice-water two-phase flow both quantitively and qualitytively.(3) A digital phase-sensitive detect circiuit and its program to detect weak impedance signals are developed, by which the seperation between real part(resistance) and image part(capacitance) is achieved in the condition of high SNA for ice-water two-phase flow measurement.(4) This paper improves the character of Voltage Controlled Current Source, namely VCCS, in the field of constant current, which strengthens the load capbility and enlarges the measuring scope of ERT system for two-phase ice and water.(5) Algorithms of image reconstruction for ERT system is developed by MATLAB, which include Linear Backprojection (LBP) algorithm, Sensitivity Coefficient algorithm, Truncated Singular Value Decomposition (TSVD) algorithm and Tikhonov Regularization algorithm.(6) In order to test the actual performance of ERT system developed, a static experiment system of ice-water two-phase flow is set up, and the image construction of dynamic distribution and variation of ice and water is tested. The result shows that the location and real-time moving state of ice column can be obtained by ERT system. Pixels of different colors are used to distinguish between water phase and ice phase. The images, which are processed by gray and binary conversion, are calculated by IPF formula. The calculated result shows that the error of phase fractions are less than6%,which indicates that our system can be used in real circumstance.The research results of this paper can play an important role in the following fields:(1) It provides a new ice-water detecting technique for the channels, tunnel, pipeline, other ice-water transfer facilities, and technical support for safe operation of national large water conservancy project in winter.(2) Our new detection technology of two-phase flow can be used in large ice storage equipments, with the characters of accurately obtaining two-phase flow pattern and IPF parameters. This technology can improve the level of real-time monitoring and automation management of refrigeration equipments.This work was supported by National Science Foundation of China(Grant No.51279122) and Shanxi Province Science Foundation for Youths (Grant No.2012021013-2).