| Gas-liquid two-phase flow exists widely in industrial process and it is closely related to the national economy.The state monitoring and parameter measurement of gas-liquid two-phase flow are of great importance.However,due to the complexity of gas-liquid two-phase flow,relevant monitoring/measurement work is still a difficulty in the research field.ET is an effective method for monitoring gas-liquid two-phase flow and implementing relevant parameter measurement.Among them,ERT technique has become popular for research due to its advantages of no radiation,good real-time performance and low cost.However,the electrodes of conventional ERT sensor are in contact with the measured fluid directly,which can easily lead to electrochemical corrosion and electrode polarization.Currently,researchers introduced C~4D technique and proposed a new contactless ERT technique,which is CCERT technique.The electrodes of CCERT sensor are not in contact with the measured fluid directly and the problem of conventional ERT can be avoided.Even though CCERT is a new technique of potential,the research related to CCERT is limited and weak.The research on measurement characteristics,image reconstruction performance of sensors under different excitation strategies is an important aspect in the research field of ET.However,the research on CCERT sensor under different excitation strategies is limited and more research should be undertaken.This dissertation is aimed at proposing a new 12-electrode CCERT system on the basis of conventional CCERT system,which can realize different excitation strategies.The measurement characteristics,image reconstruction performance and void fraction measurement performance under different excitation strategies will be investigated and compared,which can provide new method and reference for solving the relevant problems of the monitoring/measurement of gas-liquid two-phase flow.The main innovation points and contributions of this dissertation are listed as follows:1.A 12-electrode CCERT system which can realize different excitation strategies is developed and five different excitation strategies(1-electrode excitation strategy,2-electrode excitation strategy,3-electrode excitation strategy,4-electrode excitation strategy and 5-electrode excitation strategy)will be investigated.The command decoder module is improved to realize different excitation strategies.Research results indicate that the development of the new system is successful.Using LBP algorithm to implement the preliminary image reconstruction experiments,the results indicate that the reconstructed image can reflect the distribution of the measured medium.2.The sensitivity distribution characteristics of the 12-electrode CCERT sensor under the five excitation strategies is investigated by simulation.The research results indicate that under the five excitation strategies,the sensitivity distributions of the 12-electrode CCERT sensor have no negative region and are not uniform.The sensitivities near edge of field are much higher than those of other area.The average sensitivities of the sensitivity distributions of the four multi-electrode excitation strategies are all higher than that of the sensitivity distribution of the 1-electrode excitation strategy.The sensitivity distributions become more uniform simultaneously as the number of excitation electrodes increases.3.The image reconstruction performance of the 12-electrode CCERT system under five excitation strategies is investigated and compared.Four typical image reconstruction algorithms(LBP algorithm,Landweber iteration algorithm,ART algorithm and SIRT algorithm)are introduced to investigate the image reconstruction performance.The experimental data are obtained from the CCERT system and image reconstruction experiments are implemented.Research results show that the 1-electrode excitation strategy and the 2-electrode excitation strategy have better global image reconstruction performance.These two excitation strategies are better choices.4.An image reconstruction algorithm,which is developed for the 12-electrode CCERT system under 2-electrode excitation strategy,is proposed.Using L-curve and Reginska’s method to determine the value of truncation index,the TSVD method is used to reconstruct the initial image.The ART algorithm is used to obtain the final reconstructed image.Image reconstruction experiments are conducted by the CCERT system.Experimental image reconstruction results indicate that under 2-electrode excitation strategy,the proposed algorithm has obvious advantage over conventional image reconstruction algorithms.Under 1-electrode excitation strategy,the image reconstruction performance is comparable or slightly improved compared with that of conventional image reconstruction algorithms.The quality of the initial reconstructed image can be significantly improved compared with that of classic LBP,either under 2-electrode excitation strategy or 1-electrode excitation strategy.5.The void fraction measurement of gas-liquid two-phase flow of three two-phase distributions(bubble flow,stratified flow and annular flow)is investigated by the 12-electrode CCERT system under five excitation strategies.Two data processing approaches which are the data average method and the PCR method are used to establish the void fraction measurement models and hence to implement the void fraction measurement.Using the CCERT system to carry out void fraction measurement experiments,the measurement results indicate that the 5-electrode excitation strategy has the best void fraction measurement performance.The absolute values of void fraction measurement errors of the three two-phase distributions are all less than 5.0%and3.0%with data average method and PCR method,respectively.Experimental research results reveal that the 5-electrode excitation strategy+PCR combination is a new and effective way for void fraction measurement. |
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