Flow Regime Identification And Quantitative Detection Of Solid Mass Flux Under Various Flow Regimes During Particle Conveying Process

Particle conveying(pneumatic conveying and hydraulic conveying)is widely used in industrial processes due to its advantages of large conveying capacity and convenient operation.As an an energy-consuming process,it is often recommended to convey materials near the minimum conveying velocity(the conveying velocity at the minimum pressure drop)to reduce the energy consumption.However,the flow regimes in this operating zone are complex and variable,and the solid mass flux fluctuates greatly,which harms the stable operation.Therefore,based on the formation mechanism of the minimum conveying velocity,realizing the flow regime identification and the quantitative detection of solid mass flux under various flow regimes has always been a key research direction in the particle conveying field.In this thesis,taken the pneumatic conveying process and hydraulic conveying process as the research object,acoustic emission detection,pressure pulsation detection and high-speed photography are employed to obtain the particle motion information during the conveying process.By analyzing the particle motion information,the formation mechanism of the minimum conveying velocity is revealed,the flow regime identification is realized,and the quantitative detection of the solid mass flux(pneumatic conveying)/solid mass concentration(hydraulic conveying)under various flow regimes is also realized.The main research work and findings are as follows:1.For the inclined pneumatic conveying process with the most complex forces acting on particles,the evolution laws of the pressure drop and the minimum conveying velocity with the inclination angle are explored,and the theoretical analysis of energy loss reveals the underlying mechanism of the minimum conveying velocity.The results show that under the same superficial gas velocity and solid mass flux,the pressure drop first increases and then decreases with the increasing inclination angle.Meanwhile,the minimum conveying velocity increases with the increasing inclination angle,and the changing trend is bounded by 45°.When the inclination angle is smaller than 45°,the minimum conveying velocity increases rapidly with the increasing inclination angle.And when the inclination angle is larger than or equal to 45°,the minimum conveying velocity increases slowly with the increasing inclination angle.By theoretically decomposing the pressure drop during the dilute phase conveying process,combined with the particle image velocimetry technology,it is confirmed that the evolution law of the minimum conveying velocity is mainly dominated by the particle velocity.The particle velocity can significantly affect the energy loss caused by particle suspension,which in turn dominates the evolution law of the minimum conveying velocity.2.The evolution law of particle motions during the flow regime transition in the horizontal pneumatic/hydraulic conveying process is explored,a new method for flow regime identification based on the distribution characteristics of particle motions is established,and the universality of the method is investigated.The results show that the essence of flow regime transition is the change of the spatial distribution characteristics of particle motions.Based on this feature,the fluctuation distribution index(FI)constructed by the moment method and the concept of polymer molecular weight distribution index can effectively reflect the particle motion characteristics under different flow regimes.In suspension flow,the disordered particle motions cause the FI to be much larger than 1.While in slug flow,the strongly ordered particle motions cause the FI to approach 1.Furthermore,the circumferential fluctuation difference(Dpneumatic)that characterizes the circumferential difference of FI is defined,and a new criterion for flow regime identification in the horizontal pneumatic conveying process is established.In suspension flow,Dpneumatic>0;In stratified flow,Dpneumatic<0;In slug flow,Dpneumatic≈0.The new flow regime identification method can realize the accurate identification of suspended flow,stratified flow and slug flow in different conveying scenarios(different conveying materials and different conveying pipes).In addition,this method can also be extended to the accurate identification of homogeneous suspension flow and heterogeneous suspension flow in the horizontal hydraulic conveying process.3.Combined with acoustic emission detection and machine learning model,the standardization strategies of acoustic signals in different conveying scenarios are proposed,the intelligent prediction model of solid mass flux suitable for different pneumatic conveying scenarios is established,and the accurate prediction of solid mass flux in different horizontal pneumatic conveying scenarios(different flow regimes,different conveying pipes and different conveying materials)is realized.The results show that adding flow regime parameters(fluctuation distribution index FI,circumferential fluctuation difference Dpneumatic and so on)to the inputs can significantly improve the prediction accuracy under different flow regimes,and thereby reducing the prediction error from 17.3%to 8.4%.Based on the generation and propagation mechanism of acoustic signals,the original acoustic signals obtained in different conveying scenarios can be standardized to improve the similarity of them.Then,combined with the optimized machine learning network,the prediction accuracy under different conveying pipes(from 25 mm inner diameter to 40 mm inner diameter)and different conveying materials(from polypropylene to polyethylene)can be greatly improved,and the prediction error decreases from 176.0%and 218.6%to 16.2%and 20.6%respectively.4.An acoustic emission model is proposed to characterize the particle motions during hydraulic conveying process(E=Kscsu2mix),and the quantitative relationship between acoustic energy of particle motions,solid mass concentration and mixture velocity is revealed.And thereby the prediction of solid mass concentration during horizontal hydraulic conveying is realized.The results show that the key parameter of acoustic emission model(Ks)is mainly affected by the flow regime.When the flow regime is unchanged,Ks is fixed,and the acoustic energy of particle motions is linearly related to the solid mass concentration,and is quadratically related to the mixture velocity.Based on the flow regime identification results(heterogeneous suspension flow and homogeneous suspension flow),the key parameter of prediction model can be obtained through piecewise regression(3.09×107 and 2.52×107 for quartz sands,2.00×107 and 1.85×107 for slag particles),and the accurate prediction of solid mass concentration in the hydraulic conveying process of two kind of materials can be realized(the prediction error of quartz sands is 10.2%and the prediction error of slag particles is 14.0%).