Research On Flow Characteristics Of Dense Phase Pneumatic Conveying In Branch Pipeline

Pneumatic conveying technology is a logistics technology transporting solid phasematerials based on the differential pressure drive air. With the characteristics of low energyconsumption, high transmission efficiency, dense phase pneumatic conveying is widely used.Pipeline layouts of pneumatic conveying system are flexible, and the geometric structuresof pipeline are various. As one of pipeline layouts, branch pipe is commonly used to carrysupervisor and branch pipe to form a network conveying system.Due to the split line, theturning of the flow will makes the movement of gas-solid phases be more complicated in thebranch pipeline, and the change of the angle between branches and system operatingparameters will affect the flow parameters of the branch such as flow distribution and pressuredrop. Therefore, study on the flow characteristics of branch pipeline has important significancein theory and engineering.Based on the above background, we selected six kinds of pipe branch with differentgeometric structure (branch pipe is composed of fixed and variable branch) as the researchobject, and the dry fly ash as delivery materials. By changing the angle of branch pipe, masssolid loading ratio and the conveying velocity, the shunt characteristics of branch pipe, thelocal pressure drop at the branch and linear of the branch pipe were analyzed. And based on theexperimental results, mathematical models of local pressure drop and linear pressure dropwere established. At the same time, the flow field of the branch was intuitively got by usingnumerical simulation technology.In the experimental research, a pneumatic conveying system which was composed ofbranch pipe was designed and built, and experimental results shows that: Flow distribution ofthe branch pipe is mainly affected by the change in the branch angle, and gas-solid phases aremore easily allocated to the branch whose angle between the supervisor and branch pipe issmaller, and only when gas velocity is less than pipeline deposition rate, gas velocity and theratio of solid gas quality will influence on the flow distribution. The local pressure drop at thebranch and linear of the branch pipe increase with the delivery speed and the ratio of solid gasquality, there will be a turning point on the pressure drop curve when reach the deposition rate. For the theoretical analysis, through the experimental study, considering elementsinfluencing linear resistance and local characteristics of branch pipe, using dimension analysisand mathematical methods, such as multiple linear regression analysis, respectively, fitting ofthe branch tube frictional resistance and local characteristic equation, and validation to theaccuracy of the equation, found that fitting equation is accurate.For the numerical simulation, based on the experimental parameters obtained, usingGambit software to geometric modeling and meshing branch pipes, and refining meshes in thebranch and the pipe wall, choosing the Eulerian two-fluid model in Fluent software andRNG k turbulence model which can increase the accuracy of the whirlpool to numericalsimulate the branch pipe diversion flow field. Simulation results show that，the two-phasevelocity and pressure reduced after branching, and the branch of inner and outer wall had alarger velocity and dynamic pressure difference; the solid phase flowed closing to the medialwall in the branch, but more gas phase was gathered in the outer wall of branch and theturbulence was strong, leading to producing vortex easily, and the branch angle is bigger, thephenomenon of turbulence and vortex more obvious. Contrasting experimental values withsimulated values, we found that simulated results had high accuracy, which could be used topredict the information relating to flow field of the branch and distributary.