Study On The ECT/ERT Dual-modality Tomography Technique Based On C~4D

Two-phase flow is widespread in nature and industrial production, and the measurement of the characteristic parameters of two-phase flow is very important. As two important electrical tomography technologies of two-phase flow detection, electrical capacitance tomography (ECT) and electrical resistance tomography (ERT) have different suitable areas. ECT is suitable for the measurement of non-conductive two-phase flow, while ERT is suitable for the measurement of conductive two-phase flow. Due to the complexity of two-phase flow, if ECT and ERT can be fused into an ECT/ERT dual-modality tomography system, its application ranges will be greatly extended. However, the existing ECT/ERT dual-modality systems are always the direct combination of two single modality tomography systems, their structure are complicated, and the spatio-temporal consistency of the measurement can not be ensured. What’s more, the electrodes of the ERT sensor are in direct contact with the measured fluid, which will cause polarization effect and electrochemical erosion. So the application ranges of the existing ECT/ERT dual-modality systems are limited.To solve the problems in the existing ECT/ERT dual-modality systems, capacitively coupled contactless conductivity detection (C4D) technique, which is often studied in analytical chemistry area, is introduced into ECT/ERT dual-modality tomography area in this paper. Meanwhile, combined with the phase sensitive demodulation (PSD) method, this paper proposes a new ECT/ERT dual-modality tomography technique based on C4D principle. The main works and innovation points are listed as follows:(1) Propose a new ECT/ERT dual-modality tomography technique based on C4D principle. With only one electrode array and one data acquisition unit, the ECT and ERT information can be measured simultaneously. So the spatio-temporal consistency of the measurement can be ensured and the system structure can also be simplified. Moreover, the electrodes of the new dual-modality system are not in direct contact with the measured fluid, so polarization effect and electrochemical erosion are avoided and the application range of dual-modality system is extended. Meanwhile, the sensor structure and equivalent circuit model in different modalities of the new dual-modality system are analyzed. Then the sensor is simulated and modeled based on finite element method to optimize the sensor structure parameters and improve its sensitivity. The sensitivity distribution of the optimized sensor is also acquired.(2) Combined with analog phase sensitive demodulation technique, a new dual-modality system prototype based on C4D principle is developed and a series of experiments are carried out to verify the feasibility of the system. The experiment results verify its feasibility, and this system realizes the tomography in ECT and ERT modality. The image reconstruction quality is satisfactory, the reconstructed images are consistent with the simulated flow distributions, and the data acquisition speed is more than40frames per second.(3) To improve the measurement performance of the new dual-modality system, digital phase sensitive demodulation (DPSD) technique is introduced into the data acquisition unit design and its key technique is studied. Firstly, the overall structure and measurement principle of the new dual-modality system based on DPSD is presented. Then several key parameters in DPSD technique are optimized to improve the measurement accuracy. Finally, a data acquisition unit based on DPSD is developed and a series of experiments are carried out. Experiment results show that the data acquisition unit based on DPSD has high data acquisition speed and high measurement accuracy, which lays the foundation for the implement of a high speed dual-modality tomography system based on DPSD technique.