Motion Of Fine Particles Research Articles

Motion of fine particles in a temperature gradient: Experiment, visualization, and numerical simulation studies

The migration and deposition processes of fine particles under the influence of temperature gradients and fluid flow are widely prevalent. Investigating the mechanisms of particle interactions in these processes contributes to the development of efficient dust removal techniques. In this work, experimental and numerical studies of particle motion in temperature gradient fields are conducted. The research encompasses both qualitative and quantitative analyses of particle motion influenced by thermophoresis and particle diameter. Qualitative analysis reveals that the motion characteristics of particles are jointly determined by gravity, drag force, and thermophoretic force, and the diameter range that exhibiting a notable influence of the thermophoretic force is 20–30 μm. Quantitative analysis shows that the manifestations of deposition and diffusion become more evident with an increasing temperature gradient. For instance, in comparison to the working condition with ΔT = 0 K and dp = 20 μm, the deposition mass increases by approximately 23% when ΔT = -15 K; conversely, it diminishes by about 11% when ΔT = 15 K. Additionally, the Discrete Phase Model (DPM) is employed to simulate the motion of gas-solid flow. This study presents a novel visualization system to observe particle motion in gas-solid systems to elucidate the mechanisms underlying the thermophoretic effect and establish a robust theoretical foundation for thermophoretic dust removal technology.

Numerical Study on Collection Performance of Particulates in Hemispheric-Head Cyclone Separators for Fuel Cell Vehicles

A hemispheric-head cyclone separator has higher collection performance of fine particles comparing with a conventional cyclone separator with a cylindrical head. In order to optimize the shape model with hemispheric-head, we have investigated numerically and experimentally the air flow in various shape cyclone models for industrials. The purpose of this study is to develop a cyclone model for fuel cell vehicles based on the results for industrials. Since this model is installed in a fuel cell vehicle, it must be compact due to space constraints. Therefore, as the first stage of development, based on a model of a dome-shaped cyclone separator with a cyclone diameter of 54 mm, we numerically investigated the airflow in the model by changing the dust holder size and the inlet pipe connection height. The motion of fine particles was analyzed considering only drag and gravity, and the effect of internal airflow on collection performance was investigated. As a result, it is shown that the model with the low inlet pipe connection height and the small volume of the dust holder has the highest collection efficiency. It was found that even if the entry particles in the dust holder return to the conical separator part due to small dust holder, the air flow field of the highest collection efficiency model has high centrifugal separation performance by lowering the connection height of inlet pipe. It is also the most suitable in terms of space for installation in fuel cell vehicles.

Generation of dusty plasmas in supercritical carbon dioxide using surface dielectric barrier discharges

Dusty plasmas are a class of plasmas that not only have repercussions for many branches of plasma science and technology, but also thermodynamics and statistical mechanics. However, in ground-based experiments, gravity influences the dynamics and formation of plasma crystals, and the realization of zero-gravity dusty plasmas in space is very costly and time-consuming. To overcome some of these limitations, we propose dusty plasmas in supercritical fluids as a means for realizing ground-based experiments under pseudo-microgravity conditions, to study the formation and self-organization of plasma crystals. Dusty plasmas were realized by using surface dielectric barrier discharges (DBDs) generated in supercritical carbon dioxide (), and the motion of fine particles above the electrode surface was studied by high-speed imaging. The plasmas deposited charge on the particles, and the particles formed a self-organized structure above the surface DBD reactor. The particle charge estimated from the analysis of particle motion was on the order of −104 to −105e C, and the estimation of the Coulomb coupling parameter of the charged particles with a value of 102 to 104 confirmed the formation of strongly coupled plasmas.

Phoresis of inclusions in viscous media under the combined action of electromagnetism and thermocapillarity: theory

The motion of a spherical inclusion in a fluid medium under the combined action of crossed electric and magnetic fields and thermocapillarity is studied theoretically. This motion (phoresis) can be qualified as an elementary motion of fine particles in suspensions, emulsions, aerosols, and liquid foamed materials. A term is introduced into the Stokes equation for a fluid inclusion, which takes into account the thermocapillary force acting on the inclusion due to temperature nonuniformity. Boundary conditions on the particle–medium surface are formulated properly. The solution to the system of equations (Stokes equations for the inclusions and medium, boundary conditions) provides an expression for the velocity of an inclusion in a viscous conducting medium under the combined action of thermocapillarity and electromagnetism. The expression for the velocity of phoresis in dimensionless categories provides the ratio between the viscosity and thermal conductivity of the particle and medium and contains a new dimensionless term, such as the ratio between the thermocapillary and electromagnetic effects (analogue of the Weber number). The formulas derived can be used to calculate the rate of transfer in conducting suspensions and emulsions containing various inclusions. The velocity of bubbles in molten metals (Cu, Al, Fe, Ag) is calculated to show that the effects of electromagnetism and thermocapillarity are comparable. The theoretical approach can be useful for developing a flexible method in the electrotechnology of fluid materials.

Motion of Fine Particles under Interfacial Tension Gradient in Relation to Solidification of Steel

It is important to understand the behavior of argon gas bubbles and non-metallic inclusions in front of the solidifying shell in order to improve the surface quality of steel products, in the steelmaking industry. Based on a series of fundamental researches on the motion of fine particles under the interfacial tension gradient, Mukai and Lin [1] proposed a new mechanism wherein the solute concentration gradient in front of the solidifying shell, which is the interfacial tension gradient between liquid steel and particles, plays an important role in the entrapment of argon gas bubbles and non-metallic inclusions by the solidifying shell in continuous casting of steel. Developing this idea, this paper proposes Mukai-value M for use in estimating the dependence of the interfacial gradient force required to entrap the particles on solute concentrations of steel. Use of this index enables rapid quantitative prediction of the behavior of argon gas bubbles and non-metallic inclusions in the continuous casting of steel.

Motion of fine particles in liquid caused by interfacial tension gradient in relation to metals separation technologies

Some ideas for promoting the metal separation process are proposed based on the consideration of the force caused by interfacial tension gradient as a driving force. The force drives the particle toward the direction of the lower interfacial tension side, which has been confirmed by water model experiments. Therefore, it is possible to move fine metal particles by producing interfacial tension gradient between fine metal particles and molten slag. The force in molten slag–metal (iron) system was evaluated under some assumptions. The evaluation indicates that the force is enough large to engulf the fine metal particle by the interface between metal particle and slag for promoting metal separation process.

Motion of Fine Particles under Interfacial Tension Gradient in Relation to Continuous Casting Process

In front of the solidifying interface of a water solution, in the case of NaCl water solution, fine bubbles (10~100 μm in diameter) were just moving upward, no matter how close they were from the solidifying interface. However, in front of the solidifying interface of C8H17SO3Na water solution, once the distance between the bubbles and the solidifying interface became less than 90~100 μm, rising bubbles were found to move horizontally toward the solidifying interface quickly, and then to be engulfed by the interface. This effect can be attributed to the surface tension gradient around the bubbles induced by the concentration gradient in the boundary layer formed in front of the solidifying interface. The phenomenon is taken as a kind of the Marangoni effect in a broad sense. The movement of fine particles driven by the interfacial tension gradient is found to have a close relationship to certain phenomena in continuous casting processes, such as the occurrence of bubble or inclusion‐related defects in steel and nozzle clogging.

溶鋼中微小介在物粒子の運動に関するモデル実験

溶鋼中微小介在物粒子の運動に関するモデル実験

Circulatory Motion of Fine Particles in a Fluidized Bed

The average circulatory motion of solid particles in a fluidized bed affects the mixing and dispensing of fine particles. A solution of the averaged dynamic equations gives the distribution of velocities of primary circulatory motion in a cylindrical bed. General relations are given for fine powders. *Paper presented at the Second International Aerosol Conference, Berlin, Federal Republic of Germany, September 22–26, 1986.