Computational Investigation of Horizontal Slug Flow in Pneumatic Conveying

Abstract

Dense-phase pneumatic transportation of bulk materials in the form of slug flow has become a very important technology in industry. In order to understand the underlying mechanisms of slug flow, this paper presents a numerical study of slug flow in horizontal pneumatic conveying by means of discrete particle simulation. To be computationally efficient, the motion of discrete particles is three-dimensional and the flow of continuum gas is two-dimensional, and periodic boundary conditions are applied to both gas and solid phases horizontally. The proposed numerical model is qualitatively verified by comparing the calculated and measured results in terms of particle flow pattern and gas pressure drop. Then the influence of operational conditions such as gas and solid flowrates on slug behavior is numerically investigated. It is shown that slug velocity linearly increases with gas flowrate but is not sensitive to solid flowrate, and slug length increases with both gas and solid flowrates. The results qualitatively agree with the experimental observations. Finally, forces governing the gas-solid flow are analyzed on different length scales. It is shown that the movement of a slug is macroscopically controlled by the axial particle-fluid and particle-wall interactions, whereas the particleparticle interaction microscopically causes a slug to sweep up particles in a settled layer. The magnitudes of these interaction forces increase with gas and solid flowrates.

Micromechanic modeling and analysis of the flow regimes in horizontal pneumatic conveying

“…Figure 10b also shows that the radial gas velocity remains negative near the slug tail, but positive near the slug head, as observed in other studies. 58 Different from the velocity distribution, the pressure drop mainly happens inside the slug along the pipe, and is negligible outside the slug (Figure 10d), similar to that observed by Tomita et al 73 Because of the aforementioned flow properties of gas phase, the fluid-drag force shown in Figure 10f, and the pressure gradient force shown in Figure 10g, is both several times the particle gravity force inside the slug and less than particle gravity force inside the settled layers and other parts. Interestingly, it is found that the pressure gradient force has a more uniform distribution in the radial direction than the fluid-drag force, similar to those found in a vertical slug flow.…”

“…Actually, particles in the back settled layer gradually settle down when the slug moves away. For comparison, the particle-particle force, as the driving force of a slug for picking up particles in its front settled layers, 58 is given in Figure 10h. It can be seen that the particle-particle force is mainly distributed near the middle section of the slug, and can be a thousand times the particle gravity force.…”

“…The cell size used in this work is three particle diameters, in connection with our previous study. 58 For a cell close to a wall, its region out of the computational domain should be excluded. All these treatments are consistent with those used in averaging a local macroscopic property.…”

A numerical study exploring the effect of particle properties on the fluidization of adhesive particles

“…This relationship is used by a number of DEM force models, 15,16 which differ in their treatment of dissipative and tangential forces. Unlike the linear model, the mathematical expression of the Hertzian force depends on the physical properties of the particle.…”

Dilute-phase pneumatic conveying of polystyrene particles: pressure drop curve and particle distribution over the pipe cross-section

“…Morikawa (1982, 1984) studied a gas-solid flow in a horizontal and vertical pipe using different types of relatively large polystyrene spheres. Numerical modeling of pneumatic conveying of solid particles in horizontal tubes has been published by several authors (Kuang et al, 2008;Lain et al, 2009;Sommerfeld and Lain, 2009), but experimental work is still needed to determine pressure drop curves.…”