| Mixing is necessary process in industrial production,which finds many utilities in metallurgy,chemical,pharmaceutical and orher fields.The purpose of stirring and mixing is to achieve the mixing uniformity of the material system as soon as possible,so as to promote the reaction.Therefore,how to obtain the effective quantification of the uniformity of the multiphase mixing system and further improve the mixing efficiency is of great significance to the design optimization of the stirring reactor and the energy saving and consumption reduction.The high-speed photography technology can only get the image after the bubble overlapping in the mixing process due to the factors such as reflectance.There is an urgent need for a method of visualization of multiphase flow to study and explore the mixed state in metallurgical process.Considering its advantages of being non-radioactive and its fast speed,can collect the internal phase distribution map of the mixing process in real time,Electrical capacitance tomography(ECT)has the potential of metallurgical industry application.In this paper,the evaluation method and application of gas-liquid mixing effect in stirred reactor are systematically studied by using fractal dimension calculation,digital image processing technology and statistical theory.The content mainly involves the design of gas-liquid mixing experiment,the logistics evaluation method of gas-liquid mixing effect and its model research,and the qualitative and quantitative analysis of gas-liquid mixing effect.A top-blowing gas-liquid mixing experimental platform based on the capacitance tomography system was established to expound and put forward a new logistics model evaluation method for the effect of gas-liquid mixing.This method can simultaneously determine the shortest mixing time and the different stages of bubble growth.The basic theories of the evaluation of stirring and mixing is reviewed,the effects of different top blown gun flow Q、different immersion depth of the gun H and diffenent number of nozzle on the mixing effects in experiments are investigated,the effects of flow rate,insertion depth and number of nozzle on mixing effect were studied experimentally.The results show that the logistic curve based on the fractal dimension has an s-shaped growth trend with time,and the mixing time corresponding to its inflection point is the shortest mixing time.The smaller the mixing time is,the better the gas-liquid two-phase mixing effect is;with the increase of the spray flow rate and the nozzle insertion depth,the minimum mixing time shows a decreasing trend.The experimental results show that the spray flow rate in the best condition is Q= 0.65L/h and the nozzle insertion depth is L= 4cm,and the corresponding mixing time is the minimum.With the double spray gun,the shortest mixing time corresponding to the inflection point in the platform period of the Logistics curve does not decrease with the increase of the flow rate,but the excessive flow rate makes the mixing effect counterproductive.At the same time,euler property number was introduced to characterize the evolution law of bubble topological invariant in gas-liquid mixing process.Secondly,the statistical laws of mixing effects by caculatced the hisograms of the capacitance number time scries in different mixing conditions are further investigated,and the result shows that the capacitance values under different experimental conditions are approximately normally distributed.In order to clearly describe the accuracy of the normal distribution fitting,the probability distribution diagram was calculated,and the mixing effect was judged according to the curve fitting degree.Experiments show that the better the mixing effect,the better the fitting degree of the fitting curve in the probability distribution function. |
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