Study On Particle Fluidization Characteristics Of Bulk Grain Pneumatic Conveying Flow Field

Pneumatic conveying is widely used in food,chemical industry,metallurgy and other fields as a stable and reliable conveying method with flexible arrangement.However,due to the complex gas-solid phase interaction in the conveying process,the fluidization effects of bulk grain particles are obviously different under different conveying pressures and conveying methods,resulting in significant differences in the feeding time,pressure drop,gas-solid twophase velocity and particle flow state in the conveying process.In order to explore the gassolid two-phase motion law under different conveying pressure parameters and conveying methods,improve the gas-solid two-phase velocity,reduce the pressure drop and particle settlement phenomenon,this thesis takes wheat particles as the research object,based on the basic theory of gas-solid two-phase flow,and adopts simulation and test methods to study the particle fluidizing characteristics of bulk grain pneumatic conveying flow field.The main work contents are as follows:(1)Three-dimensional modeling software was used to establish the three-dimensional model of the proportional transmission device,and computational fluid dynamics simulation software Fluent was used to simulate the pneumatic conveying of bulk grain particles by axial flow.It is found that when other conditions are the same,the feeding time of 0.25 MPa,0.3MPa and 0.35 MPa is 16 s,14s and 10 s,respectively.The feeding speed is positively correlated with the conveying pressure.When the conveying pressure is too high or too low,it may cause large pressure loss and low energy utilization rate.The pressure from the inlet to the outlet of the outlet pipe will be reduced by 97.1%,96.8% and 98.1% respectively,among which the pressure drop under the conveying pressure of 0.3MPa is the least.At the same time when the end point of the feed is not reached,the gas phase velocity at the inlet of the outlet pipe is higher than that at the outlet pipe,while the particle velocity at the inlet pipe is lower than that at the outlet pipe.The gas-solid two phases complete the transformation of kinetic energy.(2)In order to reduce the energy loss in the pneumatic conveying process,improve the gas-solid mixing effect and shorten the feeding time,the rotational technology was introduced to redesign,model and simulate the pneumatic conveying and sending device of axial flow.The simulation results show that compared with the axial flow pneumatic conveying,when the cyclone pneumatic conveying pressure is 0.25 MPa,0.3MPa and 0.35 MPa,the feeding time is 13 s,10s and 8s respectively,and the feeding speed is increased by 18.8%,28.6% and 20%,respectively.The pressure from the inlet to the outlet of the outlet pipe is reduced by 94.59%,94.54% and 94.66% on average,respectively.Compared with the axial pneumatic conveying pressure drop percentage,the energy utilization efficiency is improved.Compared with the axial flow pneumatic conveying,the gas-solid two-phase velocities at the inlet and outlet are both improved.The gas phase velocities at the inlet and outlet increase by an average of 81.5%,67.5%,28.8% and 29.3% respectively.(3)The pneumatic conveying test platform was designed and built,and the corresponding test data measurement system was constructed.The axial flow and cyclone pneumatic conveying of bulk grain particles were carried out with wheat particles as the test object.The mass-time curve and particle flow state diagram under different conveying pressures and modes were obtained by sensor measurement and high-speed photography.In the test of axial pneumatic conveying bulk grain particles,the feeding time of 0.25 MPa,0.30 MPa and0.35 MPa under three different conveying pressures is 15.9s,13.6s and 11.7s respectively,and the feeding time of cyclone pneumatic conveying is 12.8s,9.5s and 8.9s respectively.Compared with the axial pneumatic conveying,the conveying speed of cyclone pneumatic conveying is increased by 19.5%,30.1% and 23.9%,respectively.The conveying speed of cyclone pneumatic conveying is higher than that of axial pneumatic conveying,and the conveying process is stable.Compared with axial pneumatic conveying,cyclone pneumatic conveying can effectively reduce the particle settlement caused by gravity and make wheat particles more evenly distributed when moving in the pipeline.