Analysis Of Gas-Solid Two-phase Flow With Multi-sized Particles In Thin Elbows

Research of gas-solid two-phase flow law in pipes has important applications in engineering. It’s not only widely used in material handling of powder and bulk in metallurgy, rapid prototyping/3D printing, chemical engineering and other industries, but also benefit for the clean-up of dirty pipes, separation or mixture of multi-sized particles, gas-solid separation and so on. Domestic and foreign scholars have done lots of experimental and numerical researches in this field. However, most work aims at pipes with a large diameter transporting mono-sized particles, while multi-sized particles mixed in the thin pipes is rarely reported. In this paper, the numerical simulation and experimental methods are conducted to explore the solid-phase flow law in a typical 90° vertical-to-horizontal thin elbow, the main work and results are as follows:Firstly, this paper uses Fluent to simulate the dilute gas-solid flow of mono-sized particles in thin elbow, then analyze the flow behavior of particles and its influence of feeding rate, conveying velocity and particle size. The study suggests that, feeding rate has little effect on the particle distribution while increasing the conveying velocity and decreasing the particle size will alleviate the particle deposition in elbows. When the conveying velocity is 18m/s, the degree where particles collide with the elbow wall is only 2° larger than that of 9m/s, which indicates that the collision position has little to do with the conveying velocity for the elbow of constant curvature radius. Analysis also shows that the collision position is mainly affected by particle size, that is, larger diameter means larger degree.Secondly, in order to explore the transport law under complex conditions, this paper makes a further research of binary and multi-sized particles mixing in the same pipe based on the mono-sized results. The study shows that, in the bend segment, the positions that particles of different sizes collide with the side wall are different, but the collision gradually attenuates with development of flow. After approximately 60°, different particle beams tend to be merged with a bunch of beam flowing along the side wall. In the vertical section, the mass center of particles shows the behavior of oscillation around the pipe center, and the oscillation will gradually decline to vanish. Besides, larger particles are oscillating more sharply, while the influence of feeding rate and conveying velocity is not significant.Moreover, considering the research conditions, a set of gas-solid two-phase flow experiment device is built with PIV technology which is used to observe the particle flow in the pipe. The experiental result is then compared with that fromthe simulation results. It is found that, the particle deposition in the simulation is more obvious than that of experiment in the horizontal section while the other parts fit well. The study indicates that, the transverse force contributing to the suspension of particles is about 0.3 times of the drag force. Sothe transverse force should not be neglected in the numerical simulation.At last, this paper summarizes the whole study, and points out the deficiency and future direction of relative research.