Hitoshi Emi

Simulation of the growing process of a particle dendrite and evaluation of a single fiber collection efficiency with dust load

Abstract The growing process of particle dendrites on a fiber and the time dependency of a single fiber collection efficiency under dust loaded conditions were studied. Monte Carlo simulation technique was used to express the growing processes of particle dendrites on a fiber in Kuwabaras cell. Fairly good agreement in shape of dendrites was obtained with experimental observations. Single fiber collection efficiency was estimated from the simulation results and it was further correlated with the mass of deposited particles in unit filter volume. Through these calculations for various combinations of Stokes number and interception parameter, the ratio of a single fiber collection efficiency to that of a clean fiber was approximated to a linear function of deposited mass in unit filter volume. The coefficient of the linear function, which was named collection efficiency raising factor, decreases as Stokes number and interception parameter increase.

Effect of Charging State of Particles on Electret Filtration

Collection performance of an electret filter with rectangular fibers was studied experimentally for cases in which electrostatic effect and Brownian diffusion are predominant by using particles from 0.02 to 0.4 μm in diameter and at different charging states. A single fiber collection efficiency ηED was found to be expressible as a function of dimensionless parameters of Peclet number Pe, and Coulombic and induced force parameters, K c and K In as, here, A, B, C, and D are the numerical constants depending upon the charging density of electret fiber. Indices of each dimensionless parameter determined through the experiment coincided with the previous theory. A maximum penetration of particles appeared in the transition region of predominant collection mechanisms, i.e., between Brownian diffusion and induced force effect, ranging smaller than 0.1 μm in diameter for uncharged particles, and between Coulombic and induced force effects, ranging larger than 0.1 μm in diameter, for charged particles. Semiempiri...

Removal of fine particles from smooth flat surfaces by consecutive pulse air jets

In order to develop an effective dry surface cleaning method, removal of fine particles by pulse air jets was experimentally investigated. A dimensionless resuspension parameter, F*, which is the ratio of drag force on particles to van der Waals adhesion force, was introduced to correlate the removal efficiency. Resuspension experiments were carried out with monodisperse PSL particles and wax particles with diameter between 0.25 and 1.1 μm on silicon wafer and glass plate. As a result, it was found that deposition process of particles on the surface (gravitational settling and impaction at a relatively low impaction velocity) has little effect on the removal efficiency and that consecutive pulse air jet is effective in the removal of fine particles. Further, F* is the key parameter in determining the removal efficiency. The prediction method for the removal efficiency by pulse air jets with F* is proposed.

Adsorption of mercury vapor on particles.

The adsorption of mercury vapor on particles was studied by using soot particles generated by incineration of sewage sludge (EP-ash) and activated carbon particles. Through the experiments, it was found that, at 298 K, the EP-ash has a fairly high adsorption capacity for mercury vapor in the order of 10/sup -6/g/g, which is between that of the ordinary soils and that of activated carbon particles. Furthermore, it was found that physical adsorption of mercury vapor on the studied particles at high temperature is described by Dubinins equation. On the basis of the equation, it was shown that EP-ash physically adsorbs very little mercury at high temperature, and therefore, most mercury in the EP-ash is chemically adsorbed or contained in a form of mercury compounds. Nevertheless, the total amount of mercury contained in the particles is very little compared to the total mercury in the exhaust gases so that most mercury behaves as a vapor in the presence of particulate matter. 8 references, 4 figures, 3 tables.

Determination of deposition velocity onto a wafer for particles in the size range between 0.03 and 0.8 μm

Abstract An experimental technique for measuring deposition velocity onto a wafer for particles with a diameter smaller than 0.8 μm by means of fluorometry was developed. Employing this technique, deposition velocities were measured for particles with a diameter between 0.03 and 0.8 μm in bipolar charge equilibrium and with one single charge at a flow velocity from 0.02 to 0.5 m s −1 for horizontal and vertical wafers in vertical downward airflow. It was found that the experimental data agree well with an equation by Liu and Ahn [Liu, B.Y.H. and Ahn, K.H. (1987) Aerosol Sci. Technol. 6, 215–224] for particles in charge equilibrium with diameters between 0.03 and 0.8 μm. When both the particles and the wafer were charged, the experimental deposition velocities agreed with the Liu and Ahn equation when adding the Coulomb drift velocity term.

Experimental study of aerosol filtration by the granular bed over a wide range of Reynolds numbers

The collection performance of granular bed filters consisting of uniform spheres with diameters of 0.5–2.0 mm was experimentally studied by using monodisperse aerosol particles ranging from 0.02 to 2 μm in diameter at superficial velocity from 0.4 to 120 cm/s. Based on the experimental data, prediction equations of collection efficiency due to individual mechanical collection mechanisms were obtained, elucidating the influence of the Reynolds number on the particle collection. Furthermore, by assuming the additivity of the individual mechanical collection efficiencies, a prediction equation applicable to the wide range of filtration conditions is proposed.

COLLECTION MECHANISMS OF ELECTRET FILTER

Abstract Collection efficiency of a single electret fiber, which carries permanent positive and negative charges, was studied. Theoretically, it was obtained by solving the equation of particle motion taking account of the induced and Coulombic forces simultaneously. When either induced or Coulombic forces dominates particle collection, the collection efficiency was found to be proportional to 2/5 power of induced force parameter KIn, and 3/4 power of Coulombic force parameter KC, respectively. However, when both forces are effective simultaneously, the efficiency was not expressed by the simple superposition of both effects because of negative interaction between both forces. Experimentally, collection efficiency of a single electret fiber was measured by using monodisperse sodium chloride particles ranging from 0.01 to 0.4 μm in diameter for filtration velocities from 5 to 200 cm/s, under different charging state of particles, i.e., uncharged, singly or doubly charged and charged in Boltzmann equilibriu...

Experimental observation of collection efficiency of a dust-loaded fiber

Abstract Time dependency of collection efficiency of a dust-loaded filter has been experimentally studied to confirm the theoretical predictions of the previous papers. The experiment was carried out in the region of inertial and interceptional collection. The experimental collection efficiency of a dust loaded fiber normalized by the corresponding efficiency of a clean fiber was found to be expressed as a linear function of mass load of captured particles in a unit filter volume: η αm η α0 = 1 + λ m . The coefficient of the linear function, the collection efficiency raising factor λ, was found to decrease from 10 to 0.1 m3/kg as Stokes number increases from 0.05 to 1. However, λ was insensitive to the interception parameter. The experimental values of λ were in qualitative agreement with a previous simulation.

Generation of nanometer size particles and their removal from air

Abstract Monodisperse nanometer size silver particles as small as 1 nm were generated by a new differential mobility analyzer and an IR ray furnace at a concentration higher than 10 3 cm −3 . The test nanometer size particles were introduced into stainless steel wire screens and circular aluminum tubes to investigate the particle rebound on solid surfaces. As a result, it was found that the particle rebound may increase the particles penetration through circular tubes when the particles are smaller than 2 nm.

Particle collection of medium performance air filters consisting of binary fibers under dust loaded conditions

Evolutions of collection efficiency and pressure drop of an air filter with dust load vary with the filter structure, such as mean fiber size, fiber size distribution, packing density, as well as the captured particle size and filtration velocity. In the present work, time change in collection performance of medium performance air filters composing of binary fibers is studied in order to clarify the effect of fiber size distribution on the collection performance. As a result, it was found that, during the period of depth filtration, the time change in collection performance of binary filters can be predicted by assigning unique fractional collection efficiency raising factors, overall collection efficiency raising factors and pressure drop raising factors of individual fibers, suggesting that there are no interactions between fibers with different sizes. This study confirms that mixing fibers with various diameters is one of the effective means to adjust the time change in collection efficiency as well as initial collection performance.