Study On Particle Deposition And Erosion Characteristics In Bend Based On Gas-Solid Two-Phase Flow

A gas-solid two-phase flow through a bend is common,such as flue gas sampling,pneumatic conveying of natural gas,etc.The deposition of the micro-particles in a sampling pipe will reduce the sampling accuracy,and the erosion of the wall of the elbow by the particles with larger particle size also has an important effect on the production efficiency and safety.It is of great academic significance and industrial application value to understand the influence of various factors on the deposition efficiency and explore the method that reduces the maximum erosion rate.In this paper,the deposition characteristics of the micro-particles in standard 90°bend the erosion characteristics of the particles with larger particle size in the bends of different structures are researched numerically.The RNG k–εturbulence model and Lagrangian particle-tracking model are used to simulate the gas-solid two-phase flow.For the characteristics of the deposition,the effect of the curvature ratio on the deposition efficiency is studied on the different walls of the 90°square bend.The influence of the cross-section shape on the deposition efficiency,and the secondary flow and the trajectories of particles are also analyzed.The results show that the deposition efficiency in a square bend is lower than that in a circular bend under identical hydraulic diameter.The particles near the side wall can move toward the inner wall under the action of the vortices of the secondary flow.When the curvature ratio is 3,as the Stokes number increases,the deposition efficiency on the inner wall increases initially and then decreases,and the particles mainly deposit in middle deflection angles range;while the deposition efficiency on the outer wall increases slowly and then increases rapidly.The deposition efficiency on the inner wall decreases with the increase in the curvature ratio.Regarding the distributions of the deposition efficiency on the outer wall,the deposition efficiency of particles with Stokes number of 0.29–1.03 increases gradually along the outer bend wall in a bend with a curvature ratio of 3;however,the deposition efficiency of particles with larger Stokes numbers starts to decrease near the exit of the bend when the curvature ratio increases,moreover,the starting point of the downward trend moves upstream.For the characteristics of the erosion,the vertical-horizontal combined bends consisting of the bend（θ₁）–straight pipe（L）–bend（θ₂）is constructed,the flow field,trajectories of particles,erosion distribution,maximum erosion rate and total annual eroded mass are studied.The results show that the combined bend has a certain flow buffering performance,and the pressure on the outer wall of the straight pipe is lower than that of the bend.The standard 90°bend and the combined bends ofθ₁=45°have an elliptic erosion zone with a"V"shape erosion scar.While in the combined bends withθ₁=15°andθ₁=30°,the"V"shape scar disappears as the length of the straight pipe is increased,at the same time,it is accompanied by the appearance and disappearance of the stripe-shaped erosion scar.In the combined bends withθ₁=15°,when the length of the straight pipe is greater than 2D,the maximum erosion rate changes from being strengthened to being weakened.The combined bend withθ₁=30°,L=1.5D,andθ₂=60°has better anti-erosion performance,and its maximum erosion rate is 60.7%lower than that of the 90°bend.Except that the total annual eroded mass in the combined bends withθ₁=15°and L≤1.5D is similar to that in a 90°bend,the total annual eroded mass in other combined bends is greater than that in a 90°bend.