Research On Electrical Capacitance Tomography And Mixing Characteristics Of Gas-liquid Mixing Process With Top-blowing Gas Agitation

Stirring is a key step in many process technologies,involving many fields such as metallurgy,petroleum,energy,and chemical engineering.In physical reactions,stirring and mixing is to obtain the uniformity of the distribution of multiple substances;In chemical reactions,stirring is used to accelerate the reaction process.Therefore,visualizing the two-phase distribution of the gas-liquid mixing process and obtaining the gas-liquid two-phase mixing characteristics are of great significance for optimizing the stirring process.The traditional methods for measuring the mixing effect include high-speed camera shooting and conductivity measurement.High-speed camera imaging has spatial overlap;the conductivity probe measurement points are not representative,and too many probes will also affect the mixing effect.Therefore,a reliable and non-invasive technical method is urgently needed to detect the gas-liquid mixing process.Electrical capacitance tomography(ECT)technology has the advantages of non-intrusive,fast response,real-time monitoring,etc.It has strong advantages and potential for industrial application in the study of multiphase mixing.This article focuses on the top-blow gas stirring gas-liquid two-phase visualization and evaluation of the mixing effect.A top-blower stirrer covered with a 12-electrode ECT sensor is designed and a top-blowing stirring test system is set up.First,a linear back projection algorithm is used to reconstruct the image of t he gas-liquid mixing process;Secondly,use the image segmentation technology based on Color Pix and support vector machine to extract image features;Then the"Three-state test(3st)"method is used to identify chaotic features in the time series of fracta l dimension of gas-liquid mixing process.Finally,the mixing time of the gas-liquid mixing process was quantified by the corrosion meter box dimension and Logistic regression analysis.The main research contents and conclusions are as follows:(1)The single-layer 12-electrode ECT sensor is designed and manufactured.When the measuring electrode height is 15cm and the width is 4.2cm,the imaging accuracy is the highest.The gas phase uses air,and the liquid phase uses synthetic heat transfer oil.The image is reconstructed using a linear back projection algorithm.Comparing the results of two single-bubble ECT imaging with a physical model,the imaging accuracy is 94.89%,indicating that it is feasible to use ECT to study gas-liquid mixing.(2)Image segmentation technology based on Color Pix and support vector machine is used to extract image features,and the flow pattern and distribution of gas phase,liquid phase and gas-liquid mixed phase are obtained;The top-blown gas-liquid mixing process can be monitored not only by real-time imaging,but also by image reconstruction offline to analyze the mixing effect.(3)Obtain the fractal dimension time series of the ECT images of each working condition,and use the"3st"method to discriminate the period,quasi-period and chaos characteristics of the fractal dimension fluctuation in the gas-liquid mixing process.By analyzing the periodic influencing factors,it is concluded that during the top-blown gas-liquid mixing process,the better mixing conditions are chaotic.(4)Finally,use the"corrosion meter box dimension"method to process the ECT image of the experimental results to obtain the time series of the slope value P of the corrosion meter box dimension.Use the logistic regression to find the i nflection point of the P value and mix the gas and liquid Time was quantified.The earliest working conditions to reach the mixing state are the air intake Q=2.0m~3/h,the insertion depth H=30cm,and the liquidus temperature T=45?.In summary,this experimental study combines ECT technology,digital image processing,and mathematical theoretical methods,which provides new ideas for the research of blowing and stirring,and the research results can help mathematical simulation personnel to correctly understand the physical characteristics of the research process.In short,ECT technology can be used to visualize the flow pattern and analyze the mixing characteristics of the gas-liquid mixing process,and the agitator designed in this paper and the data processing method used can be extended to other two-phase flow mixing research fields.