Numerical Simulation And Three Dimensional ECT Measurement Of Gas-solid Flow In Annular Pipe

Multiphase flow is widely applied in the industrial production,the thermal process is complex and the flow parameters are still set up according to experience in the production.The mechanism and movement law of gas solid flow have been researched extensively.However,the research on application of multiphase flow in annular space is relatively less,which contain both numerical simulation and experimental research.The velocity field,the temperature field distribution in annular pipe is complex and the method of detection related is less too.In this paper,the discrete phase model(DPM)and the two fluid model is used to simulate the low concentration and high concentration gas solid flow in the annular space based on computational fluid dynamics.In DPM,the gas flow is simulated by Eulerian method and the trajectories of solid particles of difference sizes at different air velocities is calculated in the Lagrangian framework.The movement and aggregation of different size particles in different wind velocity is analyzed respectively.The simulation results show that under the same wind velocity,small size particle influenced by air drag force obviously and the movement in the pipeline is random.The larger size particles affected by gravity greater and they are blown out at the bottom of the pipe smoothly.When the particle diameter is the same,the greater the wind speed,the greater the particles affected by air drag force.And a vortex is formed near the exit of inner pipe which is not conducive to the transport of particles.In the two fluid model,the velocity of solid phase flow in inclined section just under gravity is simulated,and the velocity of solid part at the monitoring point is calculated.The imaging experiment based on the direct 3D Electric Capacitance Tomography(ECT)is established.A ECT sensor with double helix structure for the annular space is designed.The three-dimensional image with high accuracy of solid medium is obtained and they can identify the cross-sectional shape and position distribution of solid part,which can also detect the parameters in axial direction such as solid position.Based on the capacitance method,cross-correlation method is used to measure the velocity of solid phase on the inclined section.the speed difference is quite small compared to the result in two fluid numerical simulation.It indicates the feasibility of the experiment and it can be 3D ECT detection complement too,which makes the measurement results more accurate.In this paper,the computational fluid mechanics and direct three-dimensional capacitance tomography technology are combined to study the gas-solid two-phase flow in the annular space.It make up for the lack of practical shortcomings in mechanical calculation and enriches the detection results of theoretical support.