Study On Gas-Solid Two-Phase Flow Characteristics And Anti-Erosion Optimization In Pneumatic Conveying Pipes

Pneumatic conveying is widely used in industrial production because of its advantages of high efficiency and environmental protection.However,problems such as pipeline resistance and elbow erosion in conveying process will lead to pipeline leakage and equipment efficiency decline.Therefore,it is necessary to study the characteristics of gas-solid two-phase flow in pneumatic conveying pipes and the anti-erosion characteristics of elbows in order to guide the safe operation and improve the conveying efficiency of industrial pneumatic conveying systems.In this paper,the gas-solid two-phase flow characteristics in the pneumatic conveying pipeline,erosion characteristics and anti-erosion structure optimization of the elbow pipe,the influence of vibration on drag reduction and the erosion of elbow pipe were studied by combining experiment and numerical simulation.The main work is as follows:(1)A experimental platform for gas-solid two-phase flow conveying system was set up to measure the variation of pressure drop with flow velocity in horizontal and elbow pipes at two particle mass flow rates.The experimental data was used to validate the reliability of the numerical method and model selected in this paper.On this basis,the flow characteristics of dilute and dense phase pneumatic conveying in pipes were studied using numerical simulation methods.The simulation results show that the deposition increases with the increasing particle size and mass flow rate,and decreases with the increasing flow rate in the dilute phase conveying in horizontal pipe.In the dilute phase conveying in elbow,the erosion of particles on the pipe wall initially decreases,then increases,and finally decreases steadily with the increase of the particle size.The erosion increases with the increase of flow rate as a power index function,and increases linearly with the increase of particle mass flow rate.In the dense phase pneumatic conveying pipelines,the pressure drop increases quadratically with the increase of the flow rate and linearly with the increase of the volume fraction of the solid phase.(2)A relatively systematic study was conducted on the erosion problem of pneumatic conveying elbow pipes.Starting from the anti-erosion characteristics of the inner wall surface of the elbows,a variety of new elbow structures such as three-point lofting elbow,elbow with groove structure,elbow with petal-shaped structure,elbow with bionic transverse groove structure,and elbow with single rib and multi-rib structure were proposed.The numerical simulation technique was used to analyse and compare the erosion resistance of these structures in detail.The results show that the three-point lofting elbow with L=80mm has the best resistance to erosion,with an improvement of 36.67%.The elbow with the groove structure has the best anti-erosion performance at θ=15° with an improvement of 25.21%.The elbow with a petal-shaped structure has the best anti-erosion performance at θ=20°,with an improvement of 17.95%.All of the bionic surface structures with rectangular grooves,triangular grooves,and isosceles trapezoidal grooves on the elbow wall exhibit varying degrees of anti-erosion performance,with the order of antierosion superiority being triangular grooves,rectangular grooves,and isosceles trapezoidal grooves.Among them,the triangular groove with 4mm groove depth,4mm groove width and 3mm groove spacing is the best,and its anti-erosion effect increases by 36.83%.For the elbow pipe with rib structure,the isosceles triangle-shaped rib with a depth of 6mm positioned at θ=25° exhibits the best anti-erosion performance,with a 44.02% improvement.(3)The gas-solid flow characteristics of pneumatic conveying pipelines under vibration conditions were studied numerically and the effects of different vibration parameters on flow resistance and wall erosion were analyzed.The results show that the drag reduction effect is better when the vibration is perpendicular to the main flow direction in the horizontal pipelines,and the efficiency of drag reduction varies in a "semi-peak shape" manner with increasing amplitude and vibration frequency.The efficiency of drag reduction for the elbows increases with increasing amplitude and vibration frequency.The maximum erosion rate for the elbow pipes initially increases and then decreases with the increase of frequency.The maximum erosion rate increases quadratically with increasing flow velocity and linearly with increasing particle mass flow rate.The larger the flow velocity and the mass flow rate of particles,the smaller the change in the erosion shape on the pipe wall compared with that without vibration.