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A discrete particle model for flows of Group A particles in Geldart's classification is studied. In general, Group A particles are fine and light, so that the adhesion force has a strong effect on their fluidization behavior. Inter-particle adhesion force of Group A particle was measured first. Secondly, the DEM–CFD coupling simulation with the measured adhesion force was performed, and the simulated results were compared with the experimental data about a small-scale fluidized bed for verification of the simulation. It was found from the results that there were considerable differences between their flow patterns. In order to reveal the cause of the differences, the effect of the adhesion force in the contact force model was studied on the motion of a single particle colliding with a wall. From the analysis on the particle–wall collision process, it is found that the spring constant used in the DEM model has a large effect on the particle's sticking behavior on the wall. The dynamic adhesion force model is proposed based on the present analytical investigation, and it is found that the present model well expresses the effects of the adhesion force on the flow structure for the case of a small adhesion effect.

A DEM-MPS coupled model for solid-liquid two phase flows is developed. Fluid motion is calculated for locally phase-averaged variables. The present model is applied to a collapse behavior of the assembly of aluminum particles in a rectangular container with and without liquid. The corresponding experiment is performed to validate the present model. The trajectory of each particle is traced by using the PTV (Particle Tracking Velocimetry) measurement. Calculated collapse behaviors agree well with the observed behaviors in the corresponding experiment. The calculated horizontal position of leading particle and particle velocity also agree well with the experimental results.

An NMR (Nuclear Magnetic Resonance) imaging technique was employed to visualize the convective motion in a horizontally vibrated granular bed. The size segregation phenomena are observed for a binary mixture of larger and smaller particles. Temporal progress of the size segregation was evaluated for three different combinations of binary mixture. The convective motion was clearly observed by MRI, that is, the smaller particles tended to fall down along the side wall, while the larger particles tended to rise through the central region. The convective motion is observed even in the plane perpendicular to the vibration direction as well as in the plane parallel to the vibration direction for all combinations of binary mixture. It was suggested that the size ratio of larger to smaller particles and of vessel to particle affected the segregation phenomena.

Generally, it is difficult to observe, without any disturbance, flow structures or velocities inside flows such as granular flows, particle-fluid flows and so on. It is effective to use a non-contact and non-destructive measurement method for such flows. In the present paper, an MRI (Magnetic Resonance Imaging) technique is employed to measure the motion and velocity inside the flows. MRI has been applied to granular flows since about 1990. Our group has studied the particle motion inside the rotating drum using MRI. The rotating drum is industrial equipment which is widely utilized in engineering processes. In the cylindrical rotating drum it is well-known that axial and/or radial segregation take place. In the present study, we use a conical rotating drum which is sometimes employed in the granulation process. The conical rotating drum is half-filled with a mixture of two different sizes of spherical particles. We varied the rotational speed. Then we investigated the effect of the rotational speed on the axial segregation pattern and observed the flow mode.

It is generally difficult to measure the particle motion inside of dense granular flows. An MRI (Magnetic Resonance Imaging) is one of the non-contacting and non-destructive measurement tools for such flows. In the present paper, the size segregation in the conical rotating drum is studied experimentally by use of the MRI. The segregation pattern in the axial direction of the drum depends on the rotational speed and can be classified into three types for the present experimental conditions. The MRI visualization of the particles suggests that the three types of the axial segregation pattern is closely related to the different types of the flow modes; cascading, cataracting and hybrid of them.

It is difficult to measure a particle motion inside a dense granular flow or a fluid-particle flow because of the existence of other particles. MRI is one of the non-invasive measurement techniques for such flows. MRI can measure the velocity distribution (tagging method and phase method), which is an outstanding advantage of the MRI measurement. This paper briefly explains the principle of the MRI measurement. Then MRI is applied to some dense granular flows or fluid-particle flows, such as rotating drums, vibrated granular beds, hopper flows and spouted beds.

Discrete Element Method (DEM) is widely applied to the numerical simulations of fluidized beds. However, the computational expense increases explosively as the number of particles increases. This issue hinders DEM from being applied to real-scale simulations. A model particle is sometimes employed in order to overcome this problem, in which real particles are replaced by larger model particles. When the model particle is used, some conditions (e. g., superficial velocity, gas density, gas viscosity, particle density) must be adjusted accordingly. Those are referred to as the ‘similarity conditions.’ In this research the similarity conditions are derived from the equations of change through a dimensionless analysis. Bubble motions are compared between the model particle cases and the real particle case to validate the proposed similarity conditions.

Generally, particles used in industrial fluidized beds have size distribution. When the size distributed particles are fluidized, they tend to segregate with each other. The segregation is caused by difference of drag force between larger and smaller particles. In the present paper, we focus on the drag force for a binary mixture of particles differing in diameter, and propose some drag force models for fluidized beds with the size distributed particle. An experiment under the same condition as the numerical simulation is performed to validate the proposed drag force models. We examine pressure drop property of the particle bed and how the segregation progresses as fluidizing time goes on both numerically and experimentally. The calculation results for each drag force model are compared with the experimental result.

The aerodynamics of particles and gas flow in a two-dimensional spouted bed (2DSB) with draft plates is investigated with the aid of the discrete element method. The geometry of the 2DSB with draft plates is set as close as possible to the experimental apparatus of Kudra [1] and Kalwar [2]. The physical properties of the coarse particles are similar to those of shelled corn. The calculated minimum spouting velocity and pressure drop agree well with the correlations of Kudra [1] and Kalwar [2]. In the spout region, the particle vertical velocities are found to decrease as the height increases. The fluid velocity in the downcomer region decreases as the superficial gas velocity increases. The particle circulation rate increases when the friction coefficient decreases or the separation height increases. At the minimum spouting velocity, the bed height does not affect the particle circulation rate in the 2DSB with draft plates. The draft plates not only reduce the minimum spouting velocity and pressure drop but also increase the maximum spoutable bed height. The effect of taking out the draft plates on the spouting phenomenon is investigated and the effect of putting in a deflector on the possible breakage of the particles is also estimated.

The solids motion in a gas–solid fluidized bed was investigated via discrete particle simulation. The motion of individual particles in a uniform particle system and a binary particle system was monitored by the solution of the Newton's second law of motion. The force acting on each particle consists of the contact force between particles and the force exerted by the surrounding fluid. The contact force is modeled by using the analogy of spring, dash-pot and friction slider. The flow field of gas was predicted by the Navier–Stokes equation. The solids distribution is non-uniform in the bed, which is very diluted near the center but high near the wall. It was also found that there is a single solids circulation cell in the fluidized bed with ascending at the center and descending near the wall. This finding agrees with the experimental results obtained by Moslemian. The effects of the operating conditions, such as superficial gas velocity, particle size, and column size on the solids movement, were investigated. In the fluidized bed containing uniform particles better solids mixing was found in the larger bed containing smaller size particles and operated at higher superficial gas velocity. In the system containing binary particles, it was shown that under suitable conditions the particles in a fluidized bed could be made mixable or non-mixable depending on the ratios of particle sizes and densities. Better mixing of binary particles was found in the system containing particles with less different densities and closer sizes. These results were found to follow the mixing and segregation criteria obtained experimentally by Tanaka et al.

The effect of pulsating gas injection on the flow pattern was studied numerically. Discrete element method was applied to the solid-phase calculation. To examine the effect of particle condition, two case of solid particles were considered : one is Group B particles in Geldart's classification and the other is Group D particles. The multiple bubbling state without pulsation was chosen as the basis gas-flow condition. In order to characterize quantitatively the effect of the gas pulsation on the flow pattern, we analyzed power spectra of the distributions of void fraction and solid velocity. The results of the present simulations suggests that the gas pulsation largely modifies the solid flow patterns in a low frequency range. Especially in the case of Group B particles, the pattern of bubbles tends to be ordered by applying the gas pulsation.

Flows in a spouted bed in a cylinder with a tapered bottom were simulated numerically. To reduce the computational load, a quasi-three-dimensional numerical simulation method for axisymmetric gas-solid flows was proposed. Fluid motion was calculated two-dimensionally by solving the locally averaged equations written in cylindrical coordinates, in which the circumferential components were neglected assuming the axisymmetry. Particle motion was calculated three-dimensionally and was traced discretely by solving Newton's equation of motion for each particle. The discrete element method (DEM) was employed to model the interaction between particles. The typical flow pattern of the spouted bed was obtained in the present calculation, i.e., a stable spout, fountain and annulus were obtained. The calculation was made for the same geometry as the experiment by Roy et al. [D. Roy, F. Larachi, R. Legros, J. Chaouki, Can. J. Chem. Eng. 72 (1994) 945–952]. The calculated spout diameter agreed quantitatively well with their experimental result. The calculated distributions of the vertical component of the particle velocity in the spout, the fountain and the annulus were compared with the experiments by He et al. [Y.-L. He, S.-Z. Qin, C.J. Lim, J.R. Grace, Can. J. Chem. Eng. 72 (1994) 561–568], in which smaller particles were used. The calculated velocity profiles agreed qualitatively well with the experimental results in spite of the difference in the particle diameter.

Dense gas-solid flows in a vertical pipe are important relating to many industrial applications; for example, standpipe flows in circulating fluidized beds or vertical plug flows in pneumatic conveying systems. In such flows, particles do not disperse uniformly in the pipes but form clusters, or generate density waves. Experimental and numerical studies have been performed for small-scale standpipe flows, and a power law have been found in power spectra of the density waves. In the present work, we analyzed the density wave in an industrialscale vertical pipe, and found the similar power law in it although the value of the exponent was different from that of the previous works for small-scale systems. We also performed a numerical simulation based on the discrete element method (DEM) coupled with CFD. The calculated value of the exponent agreed quantitatively with that in the corresponding experiment. The effect of the gas velocity on flow structure was also investigated.

A distinct element model is used to study the hydrodynamics of large-particle fluidized beds. The computed bubble rise velocity, voidage variations, averaged particle/particulate and fluid velocities are compared with the other continuum theory based on two fluid model. Based on the averaged particle/particulate velocities in a grid cell, deformation of the particle layers predicted by the two fluid model and the distinct element method are also compared. The predicted characteristics of bubble formation, motion, and eruption at the bed surface are in good qualitative agreement with the experimental observations. The quantitative differences in predicting the above parameters along with the advantages and limitations of two approaches for the case of a single isolated bubble rising in a two-dimensional fluidized bed are discussed.

An Eulerian/Lagrangian-type numerical simulation was performed on a two-dimensional fluidized bed in which the particle motion is restricted by parallel front and rear walls. Particle motion was calculated using Newton's equation of motion, and the contact forces were modeled by the discrete element method. The locally averaged equations were solved to calculate the fluid motion, taking into account the interaction between fluid and particles. Two kinds of models were used regarding the calculation of the particle motion: a two-dimensional model and a three-dimensional model. Results for both cases were compared with each other and the effect of the walls on the particle motion is discussed. Cases where partition walls are set up artificially in the bed are also calculated.

A Eulerian/Lagrangian-type numerical simulation was performed for two-dimensional fluidized beds, in which the particle motion is restricted by parallel front and rear walls. Particle motion was calculated using ordinary Newton's equations of motion, modeling the contact forces by the DEM (discrete element method). The local averaged equations were solved to calculate the fluid motion, taking into account the interaction between fluid and particles. Two kinds of calculations were performed regarding the calculation of particle motion : two-dimensional(2D) model and three-dimensional(3D) model. Results for both cases were compared and the effect of the walls on particle motion was discussed. Cases where partition walls are set up in the bed were also calculated.

Numerical simulation, in which the motion of individual particles was calculated, was performed of a two-dimensional gas-fluidized bed. Contact forces between particles are modeled by Cundall's Distinct Element Method (P.A. Cundall and O.D.L. Strack, Geotechnique, 29 (1979) 47), which expresses the forces with the use of a spring, dash-pot and friction slider. The gas was assumed to be inviscid and its flow was solved simultaneously with the motion of particles, taking into account the interaction between particles and gas. The simulation gives realistic pictures of particle motion. Formation of bubbles and slugs and the process of particle mixing were observed to occur in the same way as in experiments. The calculated pressure fluctuations compared well with measurements.

A Lagrangian-type numerical simulation was attempted for a two-dimensional fluidized bed. The availabilty of computers with large capacity opens new possibilities for treating individual particles in a fluidized bed. The solid phase in the bed was obtained from calculations of the motion of individual particles using the ordinary Newtonian equations, contrary to most previous simulations where the solid phase was regarded as a continuum. The gas phase was solved using the Eulerian equations for local variables, taking into account the gas-particle interaction. The particle-particle interaction through contact forces is a dominant factor in the case where the particle concentration becomes larger, such as in a fluidized bed. The contact forces are modeled by mechanical units such as a spring, dashpot and friction slider, in the present work.

The relation between the solid volume fraction and the attenuation coefficient of supersonic waves in suspension of large particles was investigated. Experiments were performed on the gravity flow of two kinds of spherical polystylene pellets (0.406mm and 1.50mm) in a vertical pipe. The attenuation rate was measured for two frequencies of a supersonic wave (40kHz and 200kHz). The solid fraction was measured up to about 14%. It was found that the attenuation coefficient was proportional to the solid volume fraction in the range of measurements. In addition to the experiment, theoretical calculation was carried out, assuming the particles to be fixed rigid spheres. The calculated results compared well with the measurements.

The present paper describes the discrete particle simulation of the evacuation dynamics. The inter-pedestrian forces are given by the discrete element method (DEM). The composite particle model is proposed to take into account the effect of the non-circular shape of pedestrians on the evacuation behavior. It has been indicated that the pedestrians can evacuate faster when an obstacle is placed at an appropriate position. The effect of the obstacle on the evacuation rate is also examined numerically in the present study. The proposed numerical model represents the positive and negative effects of the obstacle on the evacuation behavior qualitatively.