Seong Chan Kim

Figure of Merit of Composite Filters with Micrometer and Nanometer Fibers

We investigate the filtration performance of composite filters composed of micrometer and nanometer fibers. The filter quality is evaluated using the figure of merit, also known as the quality factor. We use analytical expressions for the pressure drop and filtration efficiency to compute the figure of merit. The effects on the figure of merit by fiber diameter, solidity, and thickness of nanometer and micrometer fibers and face velocity are investigated. Experimental data obtained using conventional filter media and nanofiber composite filters are then used to verify the calculated results. We find that for large particles (approximately 0.1 μm and above), nanofibers can improve the figure of merit compared to conventional filters. Smaller fiber size, larger solidity, and thickness of the nanofiber layer lead to better filtration performance in this size range. For small particles (approximately below 0.1 μm), nanofibers do not improve the figure of merit compared to conventional filter media. Larger fiber size, smaller solidity, and thickness of the nanofiber layer are preferred in this size range. We demonstrate that our procedure using analytical expression is a fast and effective tool for filter media design.

Carbon Nanotube Penetration through a Screen Filter: Numerical Modeling and Comparison with Experiments

Carbon nanotubes (CNTs) are being used in many applications and filtration of airborne CNTs is very important for CNT control. Penetration of airborne multi-wall CNTs through a screen filter is studied using a numerical model and the results are compared to experiments. The flow through the screen filter is simulated using a three-dimensional model, and the particle capture due to diffusion, interception and inertial impaction are covered. The length and diameter of CNTs are determined from electron microscopic images and used in the model. In the filtration experiments, the challenging CNTs are classified by a differential mobility analyzer. Therefore we compute the drag force and diffusion coefficient for CNTs based on their mobility sizes. The effects of CNT rotation and orientation on the drag, diffusion coefficient and interception length are considered in the sense of average over a large number of particles. Both the modeling and experimental results show that the CNT penetration is less than the penetration for a sphere with the same mobility diameter, which is mainly due to the larger interception length of the CNTs. The modeling results for CNTs agree reasonably well with experiments when the mobility diameter is less than 250 nm, but significantly underestimate the penetration when the mobility diameter is larger than 250 nm. The discrepancy is attributed to possible curling and bending of the longer CNTs in the flow.

Performance Evaluation of Electrostatically Augmented Air Filters Coupled with a Corona Precharger

An experimental study of electrostatically augmented air (EAA) filters coupled with a corona precharger has been conducted using Arizona road dusts and tobacco smoke. The measurements of filter efficiency and pressure drop across the EAA filter have been made using an ASHRAE 52.1-1992 filter test system and an opacity meter to measure the particle concentration upstream and downstream of the test filter. The two-stage EAA filter unit consists of the positive corona precharger upstream of a filter, to precharge particles with the electrical strength of 4.7 kV/cm, and an electrified filter collector, which has folded media with meshy metal separators, in the upstream and downstream side gaps. DC voltage of +1,000 V (1.4 kV/cm) is applied between the upstream and downstream separators to produce an electric field between the separators and media as well as across the media in a polarity so that most of the precharged particulates are collected on the upstream filter collector. A conventional filter was measured and had 70.0% efficiency with dusts of 1.96 w m in mass median diameter and 2.5 m/s face velocity, while the EAA filter had 92.9% efficiency. An electrical effect on the EAA filter was evaluated to both improve the filter efficiency and reduce the pressure drop across the filter. Also, the performance evaluation of the EAA filter using an air handling chamber system in occupied space was investigated with tobacco smoke particles.

Measurement of Metal Nanoparticle Agglomerates Generated by Spark Discharge Using the Universal Nanoparticle Analyzer (UNPA)

Nanoparticle agglomerates play an essential role in the manufacturing of many nanomaterials and are commonly found in combustion products. Conventional aerosol instruments based on equivalent spheres are not directly applicable to the measurement of nanoparticle agglomerates. The increasing interest in real-time assessment of the structure of engineered nanoparticle agglomerates and the mass concentration of potentially hazardous agglomerates (e.g., diesel soot, welding fume) makes an instrument devoted to online structure and mass measurements for nanoparticle agglomerates highly desirable. A recently developed instrument, universal nanoparticle analyzer (UNPA), utilizes the close relation between agglomerate structure and unipolar charging properties and infers agglomerate structure from measurement of the average charge per agglomerate. It was used in this study to characterize in situ the structure of metal nanoparticle agglomerates generated by spark discharge, to study the effects of sintering on the structure of these agglomerates, and to make real-time assessment of their airborne mass concentration. The primary particles sizes measured by UNPA for the gold (Au), silver (Ag), and nickel (Ni) agglomerates are in reasonable agreement with the TEM (transmission electron microscopy) sizing results, d p = 7.9 ± 1.5, 11.8 ± 3.2, and 6.6 ± 1.0 nm, respectively. In addition, findings from the study of agglomerate structural change during sintering using the UNPA sensitivity coincide with results from TEM and mobility analyses. With regard to the mass concentration of silver agglomerates at room temperature, good agreement was found under our experimental conditions between results given by UNPA, the effective density, and the gravimetric measurement. Copyright 2012 American Association for Aerosol Research

Effect of bi-modal aerosol mass loading on the pressure drop for gas cleaning industrial filters

The typical size distribution of emission particulates is bi-modal in shape with particles in the fine mode (< 2.0 w m) and the coarse mode. An experimental study of pressure drop across industrial gas cleaning filters has been conducted using a particle mixture of fine alumina and coarse Arizona dusts with a rotating aerosol disperser to generate the bi-modal test aerosol. Pressure drop increased linearly with increasing mass loading. The pressure drop was found to be strongly dependent upon the mass ratio of fine to coarse particles. The measured specific resistances of HEPA filters at a given face velocity of 5 cm/s were 1.18 2 10 6 , 5.89 2 10 5 , 4.67 2 10 5 , 2.65 2 10 5 , and 1.18 2 10 5 s -1 for the mass ratio of fine to coarse particles of fine only, 50%:50%, 25%:75%, 10%:90%, and coarse particles only, respectively. The pressure drop across the loaded filter increased with increasing face velocity. The larger the mass ratio of fine to coarse particles and the higher the face velocity are, the faster pressure drop rises. The fine particles and the greater inertia of the particle moving fast would cause a denser cake formation on the filter surface, resulting in a greater specific resistance to the gas flow.

Measurement and control of triboelectrically charged silica and glassy carbon particles

In this study, a particle trajectory analysis and charging measurements of triboelectrically charged silica and glassy carbon particles were conducted to investigate the effects of charging gas velocity and particle size on triboelectrical charging characteristics. A particle motion analysis system (PMAS) was used to measure charged particle motion information in the separation chamber with an applied uniform electric field, and the particle charging amount was calculated from the particle size and the electrostatic mobility was determined by the PMAS. The test system consisted of a particle generator, a spiral-type tribocharger made of a copper tube, and a particle motion analysis system to measure the particle size and velocity. The experiments were conducted with test particles of silica and glassy carbon and the average charging gas velocities of 6, 10, 15, 20 m/s to analyze the effect on particle charging. As a result, the silica and glassy carbon particles acquired negative and positive charges, respectively, due to the differences in the work functions, and the charging gas velocity effect on particle charge was approximately linear with an increasing velocity yielding a higher average particle charge and wider distribution.

Experimental and Modeling Studies of the Stream-Wise Filter Vibration Effect on the Filtration Efficiency

The stream-wise vibration effect of a fibrous filter is studied experimentally and numerically for the purpose of evaluating filtration efficiency. The particle sizes range from 0.02 to 10 μ m and the face velocity ranges from 3 to 10 cm/s. The vibrational peak velocity also varied from 0 to 50 cm/s. The filtration efficiency for this wide size range is obtained by combining the individual test results for fine particles (0.02 to 0.5 μ m) and large particles (0.5 to 10.0 μ m). For the fine particle experiment, Arizona Road Dust (ARD) test particles are generated by an atomizer after an ultrasonic process and measured by a Scanning Mobility Particle Sizer (SMPS). For the large particle experiment, the test particles are generated by a fluidized bed and measured by an Aerodynamic Particle Sizer (APS). When the particles are generated by the atomizer after ultrasonicating, the majority of the particles are in nano scale without the agglomerates on the large particle surface, while particles generated by the fluidized bed are mostly in micro-scale because many nanoparticles are agglomerated on large particle surface. The filtration efficiency increases with the vibrational peak velocity in the impaction-dominant region (D p > 0.1 μ m) and diffusion-dominant region (D p < 0.1 μ m), due to the increased relative velocity between the particle and the filter fiber and the increased diffusion intensity from turbulence around the fiber, respectively. A model for the filter vibration effect is established with a modified Stokes number for the impaction-dominant region and an empirical analysis for the diffusion-dominant region.

Design and Performance Evaluation of Plasma Air Cleaning Systems for Removing Yellow Sand Dust

Yellow sand dust (Asian dust storms) causes harmful damage indoors and outdoors during the springtime, and the removal of Yellow sand dust has become an issue for suitable indoor conditions. An air cleaner is required to remove Yellow sand dust efficiently to improve indoor air quality, and the removal characteristics of Yellow sand dust should be studied. The size distribution and mass concentration of Yellow sand dust observed in China and Korea are analyzed, and the removal efficiency of a plasma air cleaning system based on the principle of electrostatic precipitation is evaluated by using Yellow sand dust. Mass median diameter of Yellow sand dust sampled in Beijing and Seoul ranges from 7.0 to 8.0 μm with a mass concentration of 300-1,462 μg/m3. For a single-pass test, the efficiency of dust removal increases with increasing particle size and decreasing flow rate. The removal efficiency of Yellow sand dust in a plasma air cleaning system at a face velocity of 1.0 m/s is higher than 80%. For a multi-pass test in occupied spaces, the operation time required to reduce Yellow sand dust concentration from an initial concentration of 300 μg/m3 to 150 μg/m3 is 10 minutes for a test room of 27 m3.

FOUP purge performance improvement using EFEM flow converter

Front Opening Unified Pod (FOUP) purging with nitrogen or clean dry air (CDA) is well known as the most effective method to protect wafers inside FOUPs from internal as well as external contaminations, e.g. particles, airborne molecular contaminants, humidity and oxygen, which can potentially damage integrated circuits (IC) and significantly impact manufacturing yields. Entegris, Inc. developed a diffuser purging concept that has demonstrated exceptional purge performance over conventional methods under the FOUP door open purging condition, however some unexpected test results were reported in field tests because the diffuser purge performance is significantly affected by Equipment Front End Module (EFEM) flow patterns. Since the EFEM flow is much stronger than the purging flow, in some cases the purging flow cannot overcome the EFEM flow deflected toward the FOUP opening. Furthermore, most of the EFEM flow patterns cannot be easily defined due to the variety of the EFEM designs and operation conditions, which makes it difficult to design a universal diffuser that works with all EFEMs in the field. Therefore, a need exists to develop a simple way to mitigate the effect of the EFEM air flow on the FOUP purging flow. This research was conducted to investigate the feasibility of the EFEM flow converter (EFC) concept, which is a screen mesh installed above the FOUP opening. The test results demonstrated that the EFC can dramatically improve the diffuser purge performance by converting non-uniform EFEM flow in front of the FOUP opening into uniform downward laminar flow that is favorable to FOUP purging.

Bereitstellung von luftgetragenen Nanopartikeln für in vitro- und in vivo-Untersuchungen

Zusammenfassung:Die in vitro- und in vivo-Untersuchungen von Nanopartikeln im Hinblick auf ihre möglichen toxikologischen Wirkungen erfolgen häufig über die Aufgabe von Suspensionen auf Zellen mit aus der Nanopartikelkonzentration ableitbarer Dosis. Ein wichtiger Weg der Nanopartikelwirkung aber geht über die Inhalation. Es ist deshalb naheliegend, Nanopartikel in Form von charakterisierten Aerosolen bereitzustellen. Der Ausgangspunkt sind häufig Pulver in Form von Agglomeraten, die ohne Zerlegung in den gasgetragenen Zustand überführt werden müssen.Es werden Methoden zur Aerosolisierung von Nanopartikelpulvern vorgestellt, die zur Zeit untersucht werden. Aus der im gasgetragenen Zustand bestimmbaren Nanopartikelkonzentration kann mit Hilfe von Depositionsmodellen die auf Zellen abgeschiedene Nanopartikeldosis bestimmt werden. Für in vivo-Untersuchungen am Menschen besteht die Möglichkeit, die im alveolaren und tracheobronchialen Bereich deponierten Nanopartikelkonzentrationen unter Verwendung des ICRP–Depositionsmodells direkt messtechnisch zu erfassen.Für alle Verfahrensschritte, von der Aerosolbereitstellung und -charakterisierung bis zur deponierten Dosis, besteht Bedarf an Standardisierung.