Flow Characteristics And Stability Of Dense Pneumatic Conveying System For Grain

The pneumatic conveying technology in dense phase with suspension,in recent years,has been paid great attention to bulk,and become one of the hotspot and frontier in the field of interdisciplinary research in mechanical design,fluid mechanics,energy and power.The movement of gas-solid turbulent flow itself shows the low energy consumption,large flow rate and good grain quality,however the clogging and wear would occur.In this work,the flow characteristics and stability of grain were investigated numerically and experimentally based on the theory of fluid turbulence and particle dynamics and using the Euler-Euler model.The flow characteristics and transfer laws conveyed gas-solid two-phase turbulent were discussed by using dense phase non-uniform suspension conveying technology for Zhengzhou Dagong Grain Machinery Engineering Co.,Ltd.CXLD50 type grain absorbing machine so as to find the optimal delivery parameters for continuous delivery whit low speed and high concentration.In view of the defects such as high wind speed,low conveying ratio,serious pipeline wear,low material quality and unstable output,etc for dilute phase transport mode,the horizontal conveying of the horizontal pipe was selected considered phase-to-phase coupling effect and turbulence energy variation,and two-equation modes ofk-ewere established using the fluent simulation software to calculate the best lowest pressure drop in the delivery tube.Based on this,the Gidaspow-Gidaspow combination calculation model was confirmed,and the default value of the collision recovery coefficient is 0.92 to 0.9 for pneumatic transport of grain particles.The optimize the designs of the pipe diameter structure were worked to expound regularities of distribution on particle concentration,turbulence intensity,gas velocity and pressure loss.Compared with the results of first-order diameter change,it was finded that the pipeline structure has the advantages of low transportation speed,low pressure loss and low turbulence intensity,which can greatly improve the stability of transportation.On this basis,effect of particle density on gas-solid slip velocity and pressure drop was studied by analyzing and comparing the flow characteristics with four different values of particle density.When particle density was used from 3000 to4000kg/m~3the conveying the pressure loss and the turbulent flow energy were the smallest,and the distribution of the material concentration was the most uniform in the tube.At the same time,the optimum economic wind speed is determined to improve the continuity of transportation.Finally,experimental device for the pneumatic conveying is designed,and the flow rate and pressure loss of the granular material are detected by different inlet wind speeds according to the conveying condition.The results show that the experimental measurements are consistent with the pressure drop gradient of the prediction model,and the maximum error is within 20%.The actual measured optimal wind speed is consistent with the predicted economic wind speed.As a result,the reliability of the double Euler simulation model is proved,and the new application theory and engineering guidance are provided for improving the practical transportation efficiency and stability.