Toshitsugu Tanaka

Prediction of gas-particle dynamics and heat transfer in a two-dimensional spouted bed

Abstract The aerodynamics of particles and heat transfer of gas-to-particles in a two-dimensional spouted bed (2DSB) with draft plates are investigated by the discrete element method (DEM). The physical properties of the particles are similar to those of shelled corn. The calculated minimum spouting velocity and pressure drop agree well with the empirical correlations proposed by Kudra et al. The particle circulation rate increases when the friction coefficient decreases or the separation height increases. The draft plates can reduce the minimum spouting velocity and pressure drop. They also increase the maximum spoutable bed height. The effect of taking out the draft plates on the spouting phenomenon is investigated. The mixing of a 2DSB without draft plates of 10 000 particles is better than that of 26 000 particles. In our simulation, the gas-to-particle heat transfer is investigated. The Ranz–Marshall correlation and the correlation of Sartori et al. are applicable in the spout region and the downcomer region, respectively. The gas-to-particle heat transfer occurs mainly in the central or spout region, as reported by Freitas and Freire.

Normal viscous force of pendular liquid bridge between two relatively moving particles

In this work, Direct Numerical Simulations (DNS) of a pendular liquid bridge formed between two relatively moving particles are performed to evaluate the normal component of the viscous force exerted on the particles. The viscous force obtained are non-dimensionalised in order to clarify the parameters which can affect the dimensionless force. The DNS results are compared with the viscous force models in literature which are commonly used in DEM simulations. It is found that these models cannot be used with large inter-particle separation distance. A new and more accurate viscous force model is proposed from the DNS results which can be directly implemented in the DEM framework.

Direct numerical simulations of inertial settling of non-Brownian particles

The dynamics of particles settling at moderate Reynolds number is studied with periodic boundary conditions. The particle Reynolds number ranges from 0.1 to 50, and the solid volume fraction ranges from single sphere to 0.4. Particle-fluid interactions are solved by immersed boundary method and particle-particle interactions are solved by discrete element method. The principal results are the average settling velocity and the structure formation of particles. The average sedimentation velocities of particles for moderate Reynolds number showed deviation from the well-known power law, and the difference keeps on increasing with decrease in solid volume fractions. This deviation is removed by proposing the division of the power law into three regions of Reynolds number for dilute and non-dilute regimes. By analyzing the particle structures, this difference is due to the particle arrangements by the wake interactions at moderate Reynolds number.

Measurement of the Interaction Between a Single Particle and a Single Burgers Vortex

In the present study, as an elementary physics for modeling a particle-laden turbulent flow, interactions between a single particle and a single Burgers vortex are observed by using 2D-PIV measurement. We used three kinds of particles which have particle Reynolds numbers ranged from 1258 to 2854. Their diameters are larger than the Kolmogorov scale. The vortex Reynolds number used is 79. Especially, we focus on the vorticity field and the superficial fluid divergence field induced by the particle motion on a cross-section perpendicular to the vortex axis. It is found that the maximum vorticity is increased when the particle pass through the forced vortex area, and the increase does not occur when the particle pass through the free vortex area.Copyright

DEM Analysis of Interaction Between Granular Materials and a Cutting Blade

Cutting of granular materials by a vertical flat blade is numerically investigated using a large-scale DEM. To examine the effects of particle size on the cutting behavior and force acting on the blade, three different-sized particles with 2, 1 and 0.4 mm in particle diameter are employed. Results show that for the larger particle, the force increases with the cutting distance after the initial shear process, whereas the force profiles for the smaller particles have repeated fluctuations. The analysis of the shear band development in the materials shows that the fluctuations are attributed to the consecutive appearing and disappearing of shear bands from the blade tip. The appearing and disappearing of the bands are not observed for the larger particle case and hence it can be concluded that the development of the shear band and force working on the blade are significantly influenced by the particle size.

DEM Modelling of the Digging Process of Gravel: Influence of Particle Roundness

To improve the energy efficiency of construction and mining machineries such as hydraulic excavator and bulldozer, it is important to optimize the shape of tools, which are used to handle ground materials directly such as buckets and blades, and earthmoving processes. It is impossible without a deep understanding of interactions between mechanical tools and ground materials. In the present study, a DEM model based on multi-sphere approach is developed for the gravel excavation process using a hydraulic excavator bucket. Granular materials in nature include several geometrical factors over different scales and it is computationally expensive to model real particle shapes as they are, especially for practical engineering design problems. It is mandatory to develop a simplified model which only includes essential geometrical factors that are important for gravel-tool interactions. In the present study, the role of particle roundness on digging process is investigated. We find that smaller roundness prevents the rotational motion of particles and strengthens the shear resistance of the layer. In addition, particles with higher angular velocity are localized in a narrow zone where the formation of shear band is expected during digging processes.

Motion and Temperature of Individual Particles in Two-Dimensional Fluidized Bed With Heat Transfer

Fluidized beds are widely used in industrial processes concerned with heat transfer such as combustion, gasification, catalytic reaction and calcination. In recent years, numerical simulation models that predict the heat transfer phenomena in fluidized bed in the framework of DEM-CFD coupling simulation are developed. The heat transfer in fluidized beds is conducted by several mechanisms and its behavior is extremely complex. In order to improve these numerical models, it is important to know the relation between the convective and diffusive motion of particles and heat transfers in the particle-level. In the present study, a measurement technique based on the coupling between particle tracking velocimetry (PTV) and infrared thermography (IT) measurements is proposed. By using the technique, the motion and the temperature of individual particles and its relations with the characteristic flow structures formed in fluidized beds can be investigated simultaneously without disturbing the flow field. After careful preparations, the technique is applied to a two-dimensional gas-fluidized bed under a spouting condition and the motion and the temperature of individual particles largely-influenced by the bubble occurrences are clearly observed. The relations between convective and diffusive behaviors of individual particles and heat transfer in the bed are studied in detail.© 2011 ASME

Influence of a Gravitationally-Settling Particle on a Burgers Vortex

In the present study, as an elementary physics for modeling a particle-laden turbulent flow, interactions between a single particle and a single Burgers vortex are observed by using 2D-PIV measurement. We used three kinds of particles which have particle Reynolds numbers ranged from 1 258 to 2 854. Their diameters are larger than the Kolmogorov scale. The vortex Reynolds number used is 79. Especially, we focus on the vorticity field and the superficial fluid divergence field induced by the particle motion on a cross-section perpendicular to the vortex axis. It is found that the maximum vorticity is increased when the particle pass through the forced vortex area, and the increase does not occur when the particle pass through the free vortex area.

Characteristic Spatial Scales of Particle Clusters Formed in Gas-Solid Flow

Spatial scale characteristics of particle clusters are investigated by directly performing Fourier transform of spatial particle concentration distributions. Flow field data are obtained by large-scale Eulerian / Lagrangian simulations. All calculations are performed in three-dimensions and more than sixteen million particles are tracked in the maximum case. The inter-particle collision plays an important role for the development of particle clusters. In this study, results obtained by using the stochastic model based on direct simulation Monte Carlo (DSMC) are compared with that by the deterministic model. The results obtained by DSMC method agree quantitatively with deterministic model. Particle clusters consist of multiple-spatial scale components and the low wave-number, hence large-scale structure, is dominant. Dependency on the domain size and resolution is also investigated in detail.Copyright