Norikazu Namiki

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.

Charging of particles in unipolar coronas irradiated by in-situ soft X-rays: enhancement of capture efficiency of ultrafine particles

The charging of*ne particles in unipolar coronas irradiated by sof t X-rays (3 :5–9:5 keV ;� =0 :13–0:41 nm) was studied. Voltage–current characteristics were used to examine the corona inception voltage in presence and absence ofX-ray irradiation and to estimate the ion concentrations. The capture characteristics ofsynthesized particles: iron oxide, sodium chloride, silica and titanium dioxide, were established in coronas, with and without X-ray irradiation. Enhanced charging ofultra*ne particles in coronas was observed in conjunction with soft X-ray irradiation. A positive corona with X-ray irradiation resulted in the highest charging e)ciencies, followed by a negative corona with X-ray, X-ray only, negative corona only and *nally positive corona only. Particle charging theories available in the literature were used to qualitatively explain the observed trends. ? 2002 Elsevier Science Ltd. All rights reserved.

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.

Initial Collection Performance of Resin Wool Filters and Estimation of Charge Density

Abstract A new type of resin wool filter (RWF) that persists the load with oil droplets was developed by Kimura and colleagues. In the present work, the initial collection performances of RWF (A and C) are measured for various particle sizes (0.03, 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3 μm) with different charging states at various filtration velocities (0.05, 0.1, 0.15, and 0.3 m/s). As a result, it is shown that the present RWF impregnated with PTBP resin can attain high collection efficiency (99.999% at filtration velocity of 0.05 m/s) with a pressure drop of less than 30 Pa. The charge density is estimated by applying prediction equations of single-fiber collection efficiencies of electret filters with a dipolar charge distribution because no other prediction equation for RWF are available at present. The experimental single-fiber efficiencies for uncharged particles are successfully predicted by assigning a single value of charge density in the prediction equations for dipolar fibers. The estimated charge density on RWF fibers is 2.1 × 10− 4 C/m2, which is much higher than those of conventional electret filter media. Therefore, RWF studied in the present work is suitable for the application to respirators as well as room air cleaners.

Analysis of the drying process of seed particles in a spouted bed with a draft tube

Although a spouted bed with a draft tube is widely used in pharmaceutical particle coating to modify the release characteristics of various medicines, the coating conditions and pharmaceutical formulations are determined mostly based on experience and experiments. In the present work, we theoretically analyzed the drying process of particles by applying a cell model, which is defined as an average air volume occupied by a single seed particle. We established material balance and heat balance equations in the cell, and analyzed the drying process using evaporation flux measured by experiments. Furthermore, experiments were carried out to measure the drying process of seed particles in laboratory-scale equipment. As a result, it was found that calculated tendencies of increasing or decreasing water content of seed particles are in good agreement with the experimental data. The parameters controlling the drying process of seed particles were derived by the present analysis and the influences of these parameters discussed.

Effect of ultrasonic frequency on size distributions of nanosized mist generated by ultrasonic atomization

Ultrasonic atomization is used to produce fine liquid mists with diameter ranges below 100nm. We investigated the effect of the frequency on the size distribution of ultrasonic mist. A bimodal distribution was obtained for the mist generated by ultrasonic atomization with a wide-range particle spectrometer. The peak diameter decreased with increasing frequency, and the number concentration of the mist increased in the smaller range. We determined the relation between the size distribution of the mist and the ultrasonic frequency, and we proposed a generation mechanism for the ultrasonic nanosized mist based on the amount of water vapor around the liquid column. Increasing the power intensity and density by changing the surface diameter of the ultrasonic oscillator affected the number concentration and size distribution of the nanosized mist. Using this technique, the diameter of the mist can be controlled by changing the frequency of the ultrasonic transducer.

Degradation of organic gases using ultrasonic mist generated from TiO2 suspension.

The photocatalytic degradation of organic gases with mist particles that were formed by ultrasonic atomization of a TiO(2) suspension was performed with three different ultraviolet light sources. Three aromatic volatile organic compounds (VOCs; toluene, p-xylene, and styrene) and aldehydes (formaldehyde and acetaldehyde) were chosen as model organic gases for the degradation experiment. Under UV(365) irradiation, toluene was decomposed by a photocatalytic reaction on the surface of mist particles. Under UV(254+185) irradiation, the removal efficiency and mineralization ratio of the VOC gases were higher than those under UV(365) or UV(254) irradiation. Under UV(254+185) irradiation, it was found that VOC gases were immediately degraded and converted to water-soluble intermediates by not only direct photolysis but also oxidation by OH radical, since the removal efficiency of several organic gases depended on the reaction rate with OH radical and the primary effect of generated ozone was to complete the mineralization of the intermediates. On the other hand, water-soluble aldehyde gases were rapidly trapped by mist particles before reaction on their surface. Furthermore, water-soluble intermediates that formed via the decomposition of VOC gases were completely trapped in the mist and were not detected at the reactor exit. Therefore, notable secondary particle generation was not observed, even under UV(254+185) irradiation. Based on these results as well as the size distribution of the mist droplets, it was found that primarily submicron-scale droplets contributed to the photocatalytic reaction. Lastly, we propose a mechanism for the degradation of organic gaseous pollutants on the surface of mist particles.

Suppression of solidification of calcium-rich incinerator fly ash during thermal treatment for decomposition/detoxification of dioxins

Dioxins and dioxin-like compounds released from municipal and industrial solid waste incinerators have been a serious problem from the viewpoint of environmental pollution control. Since these compounds are concentrated especially on fly ash, supplemental treatment systems to decompose/detoxify them are required after collecting the fly ash either by a bag filter or an electrostatic precipitator. The present work is aimed at developing a heat treatment technique for fly ash, which contains a large amount of calcium (Ca) derived from hydrated lime, at a temperature higher than 500°C by adding chemical additives to prevent the solidification of Ca-rich fly ash. As calcium hydroxychloride (CaClOH) in the Ca-rich fly ash was found to cause solidification of fly ash at high temperatures, sodium hydroxide, mullite and coal fly ash were added as additives prior to the heat treatment. As a result, the additives studied in the present work are effective for decomposing CaClOH and therefore suppressing the solidification of fly ash, and yet they promoted the decomposition/detoxification of dioxins.

ENVIRONMENTAL AND SAFETY ISSUES WITH NANOPARTICLES

Publisher Summary This chapter evaluates the relationship between nanoparticles and the environment, and describes the trouble caused by nanoparticles as well as the safety issues. The relationship between nanoparticles and the environment is clarified from the viewpoint of the kind of influence nanoparticles generated either artificially or naturally have on the environment, such as in atmosphere, groundwater, wastewaters, and exhaust gases. Indoor nanoparticles originate from the several sources such as products of chemical reactions, nonvolatile residues (NVRs) of liquid droplets, printers/photocopiers, combustion, bioaerosols, and infiltration of outdoor air. The influence of nanoparticles on the indoor environment is discussed in the chapter. It describes the sources of nanoparticle generation in general industrial processes such as grinding processes, and in cleanroom or controlled environment industrial processes, such as exhaled air, ionizers, and haze by chemical reaction on solid surfaces. The chapter discusses safety issues related to nanoparticles such as possibility of dust explosion, health risks and biological effects of nanoparticle materials such as carbon nanotubes, fullerenes, nanosized metal oxides, and carbon black. The chapter also discusses methods for removing nanoparticles from gas and liquid as technology to control the influence of nanoparticles on the environment.