Investigating On Efficient Vertical Screw Conveying Theory Based On Gas-Solid Two-Phase Screw Flow

The design and manufacturing technology of vertical screw conveyor is very backward in our country,mainly due to two reasons.First,the theoretical basis of the vertical screw conveying mechanism is weak;second,the theoretical design,structural design,selection of materials and manufacturing processes are not perfect based on the above theoretical basis for an efficient vertical screw conveyor.However,design theory and methods are particularly important.In this paper,the theoretical analysis and simulation experiments are combined to study the mechanism,design theory and methods of vertical screw conveying based on gas-solid two-phase screw flow for the first time.The main research results are as follows:Gas-solid Two-phase Screw Flow Transport Mechanism.By analyzing the particles in the three fields of gas-solid two-phase screw flow field,centrifugal force field and gravity field,it is concluded that when the influence of the screw flow field is greater than the centrifugal force field,the flow field is a gas-solid two-phase screw flow state.It is beneficial to transport particles.When the influence of centrifugal force field is greater than that of screw flow field,the flow field is in a turbulent state,which is not conducive to the transportation of particles.The transport mechanism is applied,analyzed and verified in the vertical screw conveyor,and then the formula of critical screw speed is deduced based on Reynolds number.By analyzing the changes of the delivery volume and power before and after the critical screw speed,it is proved that the transport volume decreases and the power increases after the critical screw speed,which are not conducive to the efficient transportation of particles.And the correctness of the gas-solid two-phase screw flow transport mechanism is verified.Design Method of Vertical Screw Conveyor based on Gas-solid Two-phase Screw Flow.The flow characteristics of the gas-solid two-phase screw flow in the vertical screw conveyor are analyzed by E/L method and DEM+CFD coupling.The circumferential velocity distribution,axial velocity distribution and pressure distribution in the flow field are obtained.The multivariate fitting method is used to analyze the numerical data,and the average axial velocity formula and the average circumferential velocity formula of the particles are derived.At the same time the transport function and the power function are received.Flow Discrimination Based on Re-E/L Gas-Solid Two-phase Screw Flow.Firstly,the discriminating method of the gas-solid two-phase screw flow is analyzed.Then the formula of the gas-solid two-phase Reynolds number in the vertical screw conveyor is deduced by using the gas-solid two-phase dynamic viscous coefficient.Afterwards,a method is proposed for analyzing the flow state by spiral angle and swirl intensity.Finally,the correctness of the critical screw speed based on the helix angle and the swirl intensity method and the correctness of the critical screw speed based on the critical Reynolds number method are verified by the transport volume and power consumption.Gas-solid Two-phase DEM Model and its coupled simulation method based on multi-scale structures.By studying the movement density of particles in a vertical screw conveyor,a non-uniform gas-solid two-phase drag model is obtained based on the energy minimum multi-scale structure EMMS.Combining it with the gas-solid two-phase DEM model,discrete element software,and fluid dynamics,a gas-solid two-phase DEM model based on a multi-scale structure is established.The gas-solid two-phase flow in the vertical screw conveyor and its feeding head is analyzed with the above model and EDEM+FLUENT coupling tool.Based on theoretical analysis,model establishment,simulation analysis and experimental verification,this paper studies the mechanism and design theory of vertical screw conveying based on gas-solid two-phase screw flow.The research results can be directly applied to the research,design and manufacture of vertical screw conveyors and ship unloaders in China,and greatly increase the speed of our country's screw conveyors and even screw unloaders to the advanced world level.More importantly,the proposed transport mechanism of gas-solid two-phase screw flow is a brand-new project in gas-solid two-phase flow research,which has great scientific significance and value.