Electrical Impedance Measurement For Characterizing The Volume Fraction In Liquid-Solid Two-Phase Flows

Multi-phase flows widely exist in the petroleum,chemical,pharmaceutical,dredging and many other industries.The phase fraction and distribution are the key parameters in characterizing the flow structure and condition.The accurate measurements on these flow parameters are of great significance for understanding the multi-phase flow mechanics,as well as the industrial process efficiency and safety.Currently,the online non-invasive measurement of the phase fractions in multi-phase flows is still difficult to accomplish.The impedance-based measurement and imaging techniques have many advantages,i.e.,no-radiation,fast response,high dynamic range and low cost;therefore,could be investigated for the phase fraction measurements in multi-phase flows with broad prospect.This subject focuses on the characterization performance of impedance-based flow sensors in measuring the solid fraction in the liquid-solid two-phase flows,including the low frequency(below 10 MHz)and microwave frequency ranges.The main contents are as follows:1.By using Monte Carlo method,a number of effective medium approximation(EMA)models have been evaluated,regarding the feasibility and calculation accuracy in estimating the phase fraction in multi-phase flows.Numerical simulation and experimental results show that,the use of EMA models could provide the satisfied estimation results for the phase fraction,providing the experience and knowledge for the selection of EMA models in the subsequent researches on impedance-based flow sensors.2.Currently,the radioactive densitometers are still widely employed for the online measurement of slurry density/solid fraction on the cutter suction dredgers,which poses the potential radiation risk and environmental pollution.In addition,the on-site measurements cannot be transmitted remotely.Therefore,an electrical resistance tomography(ERT)system with the feature of Internet of Things(Io T)has been designed and implemented,which can achieve the functions of remote data transmission,multi-client access to the on-site data and images,etc.Combined with the EMA model,the online measurement and imaging of slurry could be carried out.The simulation and experimental results show that,the ERT system cross-sectional imaging could perform the real-time monitoring of slurry distributions and changes in the pipeline.In addition,the ERT data are in good consistency with that of the gamma-ray densitometer,demonstrating its feasibility as an online non-radioactive slurry densitometer.3.The low-frequency impedance measurement technique could be significantly affected by the conductivity changes in continuous phase,which motivates the research on measuring the solid fraction by using microwave transmission method.Electromagnetic field simulations and experiments show that,the resonance phenomenon occurs in the microwave frequency range 3～4 GHz in the impedance-based sensors,i.e.,the concave,double ring and double helix antennas.It has been found that,the double helix antenna sensor has the smallest residuals in measuring the solid fraction at 3.6 GHz.And,the absolute error of solid fraction obtained by the experimental circuit is less than 5%,suggesting its feasibility in measuring the solid fraction.It has also been indicated that,the microwave transmission method could achieve a comparatively high accuracy in measuring the solid fraction,for the water cut ratio in the range of 0～100%.