Micromechanic Modeling and Analysis of the Flow Regimes in Horizontal Pneumatic Conveying S. B. Kuang and A. B. Yu Laboratory for Simulation and Modelling of Particulate Systems, School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia DOI 10.1002/aic.12480 Published online January 18, 2011 in Wiley Online Library (wileyonlinelibrary.com). Pneumatic conveying is an important technology for industries to transport bulk materials from one location to another. Different flow regimes have been observed in such transportation processes, but the underlying fundamentals are not clear. This ar- ticle presents a three-dimensional (3-D) numerical study of horizontal pneumatic con- veying by a combined approach of discrete element model for particles and computa- tional fluid dynamics for gas. This particle scale, micromechanic approach is verified by comparing the calculated and measured results in terms of particle flow pattern and gas pressure drop. It is shown that flow regimes usually encountered in horizontal pneumatic conveying, including slug flow, stratified flow, dispersed flow and transition flow between slug flow and stratified flow, and the corresponding phase diagram can be reproduced. The forces governing the behavior of particles, such as the particle– particle, particle-fluid and particle-wall forces, are then analyzed in detail. It is shown that the roles of these forces vary with flow regimes. A general phase diagram in terms of these forces is proposed to describe the flow regimes in horizontal pneumatic conveying. V VC 2011 American Institute of Chemical Engineers AIChE J, 57: 2708–2725, 2011 Keywords: pneumatic conveying, flow regime, phase diagram, discrete element method, computational fluid dynamics Introduction Pneumatic conveying has many industrial applications and generally involves two flow regimes: dense-phase flow and dilute-phase flow. 1 The dense-phase flow conveys particles in terms of slug flow or moving bed, with power consump- tion and product damage lower than those of dilute-phase flow. The dilute-phase flow where particles are dispersed throughout an entire pipe is, however, suited for a wider range of materials. Therefore, flow regimes are of great im- portance to pneumatic conveying, particularly for horizontal pipelines, where particles exhibit more complicated behav- iors compared to those in vertical pipelines due to their gravity perpendicular to the conveying direction. The flow regimes in horizontal pneumatic conveying typically include slug flow, stratified flow, dispersed flow, and transition flow between slug flow and stratified flow. 2,3 Previous studies have shown that many variables affect flow regimes, including materials properties, operating con- ditions, and system geometries. Based on the studies of these variables, some general knowledge about flow regimes has been obtained. For example, materials and bulk properties, such as particle size and density, bulk density, permeability, air retention and deaeration, can be used to predict flow regimes, 4,5 and the characteristics of pressure fluctuation have a good capability for online identification of flow Correspondence concerning this article should be addressed to A. B. Yu at a.yu@unsw.edu.au. V VC 2011 American Institute of Chemical Engineers 2708 AIChE Journal October 2011 Vol. 57, No. 10