| Abstract
| - Dense-phase pneumatic transportation of bulk materials in the form of slug flow has become a very importanttechnology in industry. In order to understand the underlying mechanisms of slug flow, this paper presentsa 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 continuumgas 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 interms of particle flow pattern and gas pressure drop. Then the influence of operational conditions such as gasand solid flowrates on slug behavior is numerically investigated. It is shown that slug velocity linearly increaseswith gas flowrate but is not sensitive to solid flowrate, and slug length increases with both gas and solidflowrates. The results qualitatively agree with the experimental observations. Finally, forces governing thegas−solid flow are analyzed on different length scales. It is shown that the movement of a slug ismacroscopically controlled by the axial particle−fluid and particle−wall interactions, whereas the particle−particle interaction microscopically causes a slug to sweep up particles in a settled layer. The magnitudes ofthese interaction forces increase with gas and solid flowrates.
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