Wettability of a solid by a liquid plays a key role in achieving the purpose of the process in moving bed-type reactors. In recent years, particle method has been proposed for the design of processes which include multiphase flows. Using this method, it is possible to analyze a free surface flow without explicitly tracking the interface. Although surface tension and wettability models using the particle method have already been proposed, the complexity of calculations of normal line and curvature of the surface particle has been pointed out as a problem. In this study, surface tension and wettability model were introduced in terms of interparticle potential, and theoretical and experimental verifications were performed for a 3-dimensional particle method which stabilizes the internal pressure distribution in fluids. The analytical solution for the droplet oscillation period by this method showed good agreement with the theoretical solution, and the surface tension between a gas and liquid could be calculated correctly. Because the difference in the number density of a liquid phase and solid phase becomes remarkable in a 3-dimensional space, a technique which corrects for this in particles at a three-phase interface was introduced. Time change in the droplet shape was compared with the experimental results by changing the droplet impact velocity to obtain agreement of the Weber number. It is considered possible to express the droplet shape correctly during rotating falling on a solid surface.
Recently, discrete element method (DEM) had been applied for simulation of the blast furnace. For mitigating computation load and precise simulation of blast furnace, the determination of optimum physical parameters in DEM are very important. In the present study, influence of variation of hardness, rolling friction coefficient of particle and descending velocity on the solid flow and stress distribution in the blast furnace were investigated. Decreasing hardness of particle does not affect on shape of layers descending in the shaft, and causes acceleration of computation. However, stream line of particles and stress distribution vary with changing in hardness of particle. The softening of particle is not suitable for analysis of stream line and stress distribution of packed bed in the blast furnace. Stream lines of particle become smooth with an increase in the rolling friction coefficient. The value of the rolling friction coefficient should be controlled for representing shape of actual burden. It is confirmed that descending velocity of burden also affects on the stress distribution of the packed bed. Physical properties and calculation condition should be optimized depending on the purpose of analysis and phenomena in the blast furnace.
Fig. 1. Principle of the simulation model. model for granulation should be discussed. There are two models for the simulation of granulation process. One is trace movement of all particles. The other is trace movement of granulated particle only as one particle. The former might be better to analyze granulation mechanism. However, it is not realistic to simulate them because particles traced are enormous and it would take a long time to simulate the behavior of granules. Therefore the latter is adopted in this work. The assumptions in this simulation model are follows; 1) Granules are treated as one particle. 2) Particle shape is sphere. 3) Particle diameter is uniformly. 4) Particle diameter and other parameter is fixed in the simulation. 5) Effect of moisture is ignored.Physical constants and simulation conditions are shown in Table 1. Figure 2 shows the schematic diagram of a continuous drum mixer used in the simulation. Table 2 lists the size of drum mixer. Drum length and gradient angle were changed to investigate their effects on the granule behavior. The granules are fed at the extreme right of the drum mixer and granules drop from the extreme left (Fig. 2). Feeding rate is fixed at 100 kg/min. Continuous Drum Mixer Determination of ParametersThe simulation parameters are needed to be determined so that the granules behavior simulated correspond to the experimental results. Particularly the frictional coefficient has to be determined carefully since it strongly affects granules behavior. The simulation of granules behavior was performed to investigate the frictional coefficient on the behavior. The snapshots are shown in Fig. 3. The granules behavior is influenced by the frictional coefficient and a rising angle increases with an increase in the frictional coefficient. The rising angle was defined as shown in Fig. 4(a) to evaluate the granule behavior and to compare to experimental results. Figure 4 (b) shows relationship between the friction coefficient used in the simulation and the rising angle. The rising angle obtained from the experiment was also shown in Fig. 3. The rising angle increases with an increase in the ISIJ International, Vol. 49 (2009) frictional coefficient until the coefficient is 0.5, and then, the rising angle is going to be constant value about 100 degrees. The frictional coefficient was determined as 0.7, at which the rising angle obtained from the simulation is the closest to experimental one, although the rising angle obtained from the simulation does not agree with experimental results completely. This difference between them could be due to the assumption of sphere in the granules. The reason of this difference will be investigated more detail in the future. ExperimentGranulation experiment has been performed by using the continuous dram mixer. Granulator consists of rotating drum mixer, water nozzle and feed hopper (Fig. 5). The raw materials used in the actual process are supplied continuously at the extreme right of the drum mixer. Water is sprinkled by a nozzle, and ...
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