Filtration Of Fine Particles Research Articles

Magnetic Filtration of Fine Particles from Gas Streams

Dust particles from the basic oxygen furnace steelmaking process were removed from air streams using a laboratory high-gradient magnetic filter. Particle sizes and number concentrations were determined by an optical particle spectrometer and were found to be largely in the submicrometre range. Dust loadability increased greatly when a magnetic field was applied and showed no deterioration in filter performance, even though the matrix had captured 10 times its own volume of dust. Particle penetrations of 1 per cent and less were achieved for submicrometre particles down to an optically measurable 0.24 μm diameter. Varying only one parameter at a time has isolated the individual effects of filter length, magnetic field, matrix packing fraction, gas velocity and wire size and aspect ratio. The dimensionless groups in an idealized single-wire model for high-gradient magnetic filtration are not adequate for a real filter. Other dimensionless parameters, viz. average dimensionless wire separation and cumulative dimensionless wire blockage, arise and are found to be important.

Finite element modeling of ultra fine particle filtration by a membrane filter

AbstractTheoretical work has been carried out to investigate the filtration of ultra fine aerosol particles in a membrane filter. The analysis was done using a finite element method with a Newtonian fluid model for the carrier medium. Both inertial filtration and diffusional filtration were considered. Prior to the main analysis, our numerical scheme was tested with the analytical results for the diffusion of particles in the cylinder and showed good agreement, which confirms the importance of axial diffusion occurring in a short cylinder like a very thin membrane filter. Particle size, porosity, pressure drop, and flow velocity are found to be main variables that determine the filter efficiency. Two important mechanisms of filtration have opposite effects on the efficiency, depending on the variables. Increases in particle size, pressure drop, and flow velocity cause increases in the efficiency for intertial deposition, while decreases in those variables cause increases in the diffusional efficiency. The existence of a minimum value of total filtration efficiency (sum of inertial efficiency and diffusional efficiency) was indicated for intermediate values of the variables. Lower porosity is found to favor inertial deposition more than diffusion. Some other effects of filtration conditions on the total efficiency are also discussed.

Magnetic separation of fine particle dusts using a superconducting magnet and wire meshes

We have observed a phenomenon that flow patterns of gases are influenced by a magnetic field. To explain this phenomenon, a model called a ‘‘magnetic curtain’’ has been introduced. In this paper we apply this phenomenon to magnetic separation of fine particle dust in air. We use a superconducting magnet and fine ferromagnetic wires to obtain high magnetic field and high field gradient. Magnetic separation of fine particles is well realized. The efficiency of fine particle filtration increases with increasing magnetic field and also increases with particle size. The percentage of captured particles is 80% for particles larger than 1 μm, 60% for 0.5–1.0 μm, and 35% for 0.3–0.5 μm, respectively, when the field intensity is 4.5 T and the gradient is 1500 T/m.

Transport Properties of Granular Porous Media

ABSTRACTThis paper is concerned with two related problems: (1) the construction of geometrical models of porous media relevant to granular composites and (2) the description of transport processes in these model systems. We will show that a variety of interesting porous media can be generated by the packing and subsequent modification of spherical grains. This modification may involve a change in either the grain's size, shape, or both. Steady state transport processes such as the flow of electrical current or viscous fluids are controlled by the distribution of pore throat sizes and, within the presentframework, can be studiedefficiently by random walk simulations of diffusion. The techniques developed here are also of interest in connection with dynamic transport processes such as the filtration of fine grained particles into consolidated granular networks. Wediscuss briefly the modeling of such processes as well as the interaction of steady state and dynamic transport.

特集 微粉末・微粒子・超微粒子技術 微粒子フィルタ技術

特集 微粉末・微粒子・超微粒子技術 微粒子フィルタ技術

Migration of137Cs Adsorbed on Fine Soil Particles through Soil Layer, (II)

In order to study the migration behavior of 137Cs adsorbed on fine soil particles, distilled water was introduced into the unsaturated sandy soil column which filtrated the fine soil particles. From the concentrations of 137Cs in the effluent and in the soil column, it was found that fine soil particles filtrated by the soil layer were re-suspensible at the surface of soil layer and the amount of re-suspension per unit time was in proportion to the amount of filtrated fine soil particles. Considering the filtration of fine soil particles by soil layer, the reaction between soil layer and fine soil particles on which 137Cs is adsorbed is described by the formula ∂Q/∂t = K1C--K2Q at the surface of soil layer. Good agreement was obtained between the observed 137Cs concentration in the effluent and the predicted one employing ∂Q/∂t = K1C-K2Q and ∂Q/∂t = K1C as a reaction formula at the surface of soil layer and in the subsurface part of the soil layer, respectively.

Low-turbulence flocculation as an aid to vacuum filtration

The use of polyelectrolytic flocculants as sedimentation and filtration aids is standard practice in many industries where solid—liquid separation is The role of flocculation in the filtration of fine particles is discussed and the ideal flocculated structure for vacuum filtration described. A novel

Migration of 137Cs adsorbed on fine soil particles through soil layer. (II). Re-suspension of fine soil particles filtrated by unsaturated soil layer.

In order to study the migration behavior of 137Cs adsorbed on fine soil particles, distilled water was introduced into the unsaturated sandy soil column which filtrated the fine soil particles. From the concentrations of 137Cs in the effluent and in the soil column, it was found that fine soil particles filtrated by the soil layer were re-suspensible at the surface of soil layer and the amount of re-suspension per unit time was in proportion to the amount of filtrated fine soil particles. Considering the filtration of fine soil particles by soil layer, the reaction between soil layer and fine soil particles on which 137Cs is adsorbed is described by the formula ∂Q/∂t = K1C--K2Q at the surface of soil layer. Good agreement was obtained between the observed 137Cs concentration in the effluent and the predicted one employing ∂Q/∂t = K1C-K2Q and ∂Q/∂t = K1C as a reaction formula at the surface of soil layer and in the subsurface part of the soil layer, respectively.

High gradient magnetic filtration of fine particles from a gas stream

AbstractDust particles originally generated by two steelmaking processes were dispersed in an air stream and passed through a pilot‐scale high gradient magnetic filter. In accordance with theoretical predictions, the experimental results showed that collection was improved by increasing the depth or density of the steel wool filter, increasing the applied magnetic field, or decreasing the filtration velocity. Collection efficiency increased with particle size up to about 2 μm, above which the efficiency tapered off, apparently due to reentrainment effects. Collection efficiencies of greater than 99% were obtained, indicating that high gradient magnetic filtration may be a practical method of controlling particulate emission from processes in the iron and steel industry.

Filtration efficiencies in electrostatically augmented granular beds

Fine particle filtration efficiencies of electrically enhanced granular beds are computed and compared with available experimental data. Collection efficiencies of a single bed sphere in a gaseous flow are first calculated by numerically solving the equations of particle motion. The collection mechanisms incorporated here are inertial impaction, interception, and charged fine particle-imposed electric field interaction. The approach is based upon a “unit cell” model which enables one to include the effects of surrounding bed particles on the collection process. Stokes' flow and potential flow are used to model the gas flow around the bed particle. Total efficiency is computed by integrating the single-sphere collection efficiency over the bed volume. These calculated total bed efficiencies compare satisfactorily with data obtained from an existing granular bed facility over a range of parameter values. Both theory and experimental data show that the electrical force significantly enhances particulate collection in granular beds.

Mechanisms of fine particle capture by larval black flies (Diptera: Simuliidae).

Larval black flies remove fine particulate matter from stream water using a mucosubstance which coats their filtering organs (cephalic fans). This mechanism, common among filter feeding marine invertebrates, but not previously reported in freshwater insects, explains how simuliids capture fine particles (0.091 – ca. 30 μm) which would otherwise escape the cephalic fans. Investigations of two theoretical filter feeding models revealed that direct interception is probably the predominant mode of fine particle filtration for black flies. The ability of simuliids to capture fine particles, which are abundant in many streams and often support a rich nutritive microflora, may account in part for their occurrence and success in diverse lotic habitats.

Filtration of a Dilute Suspension of Fine Particles Using Glass-Fiber Papers

Several qnantitative experiments were carried out on the filtration of fine particles of polystylene in dilute suspension using various glass-fiber paper filters. Each experimental run was performed at constant filtration rate by forcing the suspension through the filter using a syringe-type micro-injection pump. From the experiments, the following results were obtained within the range of experimental conditions.1) The so called log-penetration law is applicable to the thickness of paper filters. The basic equation for filtration could be expressed as eq. (3).2) The collection efficiency of a single fiber with the interference effect is given by eq. (13). The effect of direct interception seems to be the predominant mechanism for the collection of fine particles in dilute suspension in pure water by the glass fibers.Further studies are necessary on the effect of both the fibrous solid fraction in a paper filter and electrostatic forces on the collection efficiency in order to elucidate the proportionality constant in eq. (13).