Investigation Of Complex Permittivity/conductivity Distribution By Electrical Tomography

Multiphase flows are widely existed in many industrial processes,likes energy,chemical,petroleum,metallurgy,pharmaceutical industry.Accurate measurement of the multiphase flow parameters is the key to optimize and control the process to improve the process efffcieny.Electrical tomography,as an industrial imaging technology,has the advantages of non-intrusive,non-invasive and non-radiative,and has been widely used in multiphase flow measurement.However,due to the complex multiphase flow characteristics involved in the industry process,it is difficult to directly measure the flow parameters.For example,in the pharmaceutical coating and drying process in a fluidized bed,the permittivity significantly changes due to the particle's moisture change.With the increase of mositure content,the fluid changes from non-conductive to low conductive.Similarly,in oil exploitation and transportation process,the heterogeneity of oil and water phase distribution results in the change of conductivity.For the above industrial process,the conventional single-modual tomography is difficult to meet the measurement requirements due to the change of permittivity and conductivity.It is important to provide accurate measurement for the permittivity and conductivity distribution and to control the multiphase flow process.The main target of this research is to investigate the application of electrical capacitance tomography(ECT),electrical resistance tomography with voltage excitation(ERTv)and electrical resistance tomography with current excitation(ERTc)on the multiphase flow with complex permittivity and conductivity distribution.The final objective based on the above research is to provide suitable tomography modual for different multiphase flow process.This research focused on the analyses of ECT,ERTc and ERTv performance in term of themeasurement principle,sensor design,sensitive field distribution and image reconstruction algorithm,and evaluates the stability of ECT,ERTc and ERTv systems based on the parameter of signal-to-noise ratio(SNR).To evaluate the effects of permittivity and conductivity on image quality for different type of tomography,static experiments are carried out with test materials of corn flour with moisture content of 10%-40%and saline water with conductivity of 308?S/cm-2560 ?S/cm under different flow patterns.Linear Back Projection(LBP)algorithm is used for image reconstruction.The reconstructed image is quantitatively evaluated by correlation coefficient,and the fluctuation of normalized measurement data is analyzed.The results show that the image qualities of ECT,ERTc and ERTv strongly depend on the flow patterns in experiment.ECT has better performance in the flow regime of core flow than in the bubble flow.The reconstructed image agrees well with the true distribution when the water content is less than 20%.ERTv performs better in bubble flow regime than in core flow regime,and the image qualities are especially good for wet particles with higher water content and the conductivity should be no more than 2560?S/cm.ERTc also has better performance in bubble flow regime than in core flow regime,and the phenomenon of "diagonal line" is obvious when bubbles are in the center of the measured area.In addition,ERTc behaves well in the multiphase flow with continuous phase conduction.