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.

Pneumatic conveying is an important technology in industries to transport bulk materials from one location to another. Different flow regimes have been observed in such a transportation process depending on operational conditions, but the underlying fundamentals are not clear. This paper presents a three-dimensional numerical study of vertical pneumatic conveying by a combined approach of discrete element model for particles and computational fluid dynamics for gas. The 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 vertical pneumatic conveying and their corresponding phase diagram can be reproduced. Then forces governing the behavior of particles, such as the particle-particle, particle-fluid, and particle-wall forces, are analyzed in detail. It is shown that the roles of these forces vary with flow regimes. A new phase diagram is proposed in terms of the key forces, which can successfully identify dilute-phase flow and dense-phase flow in vertical pneumatic conveying.

The compaction process of Fe and Al composite powders subjected to single action die compaction was numerically modeled by FEM method. The relationship between the overall relative density and compaction pressure of the compacts with various Al contents was firstly identified, and the influences of Al content on the local relative density, stress, and their distributions were studied. Then the compaction pressure effects on the above properties with fixed Al content were discussed. Furthermore, detailed flow behaviors of the composite powders during compaction and the relationship between the compaction pressure and the ejection force/spring back of the compact were analyzed. The results show that: (1) With each compaction pressure, higher relative density can be realized with the increase of Al content and the relative density distribution tends to be uniform; (2) When the Al content is fixed, higher compaction pressure can lead to composite compact with higher relative density, and the equivalent Von Mises stress in the central part of the compact increases gradually; (3) Convective flow occurs at the top and bottom parts of the compact close to the die wall, each indicates a different flow behavior; (4) The larger the compaction pressure for each case, the higher the residual elasticity, and the larger the ejection force needed.

The breakthrough route involving a reduction shaft furnace operated with pure hydrogen gas (here called H 2-SF) and the electric arc furnace is widely accepted as one of the most viable future alternatives for industrial-scale production of primary steel with minor CO 2 emissions. It has been clarified that the largest portion of the total energy for the entire route is consumed by the H 2-SF operation, but this unit has not yet received much attention and should therefore be explored. For this, a mathematical model of a reduction shaft furnace is presented in this paper, where a set of simulations were also performed to shed more light on the operation of the H 2-SF equipped with a top gas recycling system. The results show that a high gas feed rate is required for guaranteeing a smooth H 2-SF operation due to the strong heat demand. An increase in the feed temperature of the gas or in furnace height can reduce the required gas feed. However, an excessive length may conversely result in an increase in the total energy consumption. The model and its results are expected to be helpful for gaining a better understanding of the complex processes in and constraints of the H 2-SF.

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The present investigation was aimed at elucidating solid particle behaviour in a new design COREX shaft furnace using a new technique called areal gas distribution (AGD). The measurement of solid flow profile was performed with a semi-cylindrical model. To guarantee similarity of conditions, a modified Froude number was taken into consideration in the physical model constructed. The solid flow characteristics in this new furnace with different blast volumes were analysed, and the effect of discharge rate as well as abnormal conditions on solid flow behaviour have also been investigated. The work reveals that solid flow profile in the shaft furnace model progresses through a FlatRWaveRW shape profile as the burden descends. Blast volume has little influence on solid particle behaviour. However, increasing the discharge rate has an effect of decreasing the quasi-stagnant zone size and with the increasing discharge rate, the cross-section of AGD channel increases. For asymmetric flow, particles descend from the top and move to the discharging outlet and a very big stagnant zone is formed on the opposite side of the discharging outlet.