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.

Electret filters are frequently used in air cleaners because they have a lower pressure drop than the mechanical filters at the same collection efficiency. Manufacturers of electret filters have tried to increase the electrical charge density of electret fibers in order to improve the collection performance. Through these efforts, high-performance electret filter (HPEF) is developed and a question is raised on whether the previous prediction equations for collection efficiency are applicable to these HPEF because the prediction equations were never tested for such high charge density electret filters. In the present work, we measured the collection efficiencies of recently-developed HPEF and studied the applicability of previous prediction equations for collection efficiencies. As a result, HPEF had the electrical charge density twenty times as high as that of the previously-studied electret filter and the single fiber efficiency was close to the maximum limit determined by the packing density of fibers. Furthermore, it is found that the electrical charge of HPEF is fairly stable against organic solvent, leaving one-third of initial charge after soaking it with ethanol.In predicting the collection efficiency of HPEF, the conventional equation can be applied to the collection by induced force, however that by Coulombic force is not applicable because the single fiber efficiency due to induced force and Brownian diffusion is high and close to the upper limit without the collection by Coulombic force.

Filters consisting of fibers with irregular cross-sections are commonly used ill cigarettes. However, the influence of fiber cross-sectional shape on the filter collection performance is not well understood. In the present study, the influences of fiber cross-sectional shape on both diffusional collection efficiency and pressure drop are studied both theoretically and experimentally when the fibers were placed perpendicular to the airflow. As a result, it is found that fiber cross-sectional shape and fiber orientation have little effect on the single fiber collection efficiency, but drastically change the pressure drop. The dimensionless drag force of irregular fibers is weil correlated by the width of irregular fibers projected in flow direction because the projected width of fiber determined the mutual influence of neighboring fibers. The result suggests that the use of irregular shape fiber fitter is one of the effective means to alter the pressure drop without changing collection efficiency of the filter.

The dynamic mechanical properties of hybrids of chlorinated polyethylene (CPE) and 3,9-bis[1,1-dimethyl-2[beta-(3-tert-butyl-4-hydxoxy-5-methylphenyl)propionyloxy}ethyl] -2,4,8,10-tetraoxaspiro[5,5]-undecane (AO-80) were investigated. The CPE/AO-80 hybrids showed a novel relaxation in addition to the glass transition of CPE. The novel relaxation is attributed to the dissociation of intermolecular hydrogen bonds within the AO-80-rich domain. The Payne effect, that is, the decrease of the storage modulus E ' with increasing strain amplitude and the appearance of a loss modulus E " maximum at a strain of 0.6%, was observed for the CPE/AO-80 hybrids. This result demonstrates that the AO-80-rich domains within matrix polymer CPE form a network. The Payne effect is considered to be attributed to the mechanical disruption of segment-segment contacts at a sufficiently great strain. (C) 2001 John Wiley & Sons, Inc.

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.

Silica particles generated with Raskin nozzles are suggested as a substitute for DOP (dioctyl phthalate) particles for testing HEPA Filters. However. the generation characteristics of Raskin nozzles from the silica suspension are not well understood yet. The present work investigates the generation characteristics of Raskin nozzles for silica particles by measuring the size distribution, the mass or number concentrations of silica particles and their electrical charges. As a result, (i) although atomization pressure increases mass or number concentration. the size distributions remain rather unchanged, (ii) suspension of smaller primary silica particles generates smaller agglomerated particles with a higher mass concentration, and (iii) a higher concentration of suspension does not necessarily generate a higher concentration of particles. Further, the light scattering characteristics of silica particles by LPC were evaluated by classifying the silica particles according to the electrical mobility. The LPC underestimates the size of silica particles by a factor of about 1.6 compared to DOP particles, leading tu a serious deviation in particle penetration through air filters. Special caution is required for the light scattering characteristics and electrical charge when silica particles are used as a substitute of DOP particles for filter test.

The performance of the newly developed electrical mobility analyzer which classifies ions in axial direction of gas flow was confirmed with a favorable comparison with the value measured by a masspectrometer. The analyzer was capable of detecting ions as well as nanometer sized particles and suggested that a low concentration of SO2 triggers the nucleation of nanometer size particle at water content of 3500ppm.

The fiber size of HEPA (High efficiency particulate air) filters has been drastically decreased in the pursuit of higher collection performance, i.e., high collection efficiency and low pressure drop. The reduction of fiber size as well as the importance of collection of ultrafine particles has raised various problems in particle collection at extremely low Peclet numbers, Pe. The present work focuses on clarifying the filtration problems at low Pe by studying the collection characteristics of ideal model filters. The main findings of the present work are: (1) the log-penetration equation is not valid at low Pe because single fiber efficiency in the vicinity of the filter surface is higher than the inside; (2) filter with a lower packing density has a higher collection performance for Pe<1; (3) the single fiber efficiency of an inclined fiber can be predicted with the prediction equation for perpendicular fibers by defining Pe based on the airflow velocity component normal to the fiber axis; and (4) the effect of inclined fibers on the particle penetration is not significant so the assumption of perpendicular fiber alignment to the main airflow can be introduced without loss in accuracy.

Estimation of particle penetration through HEPA (High Efficiency Particulate Air) filters with the conventional filtration theory requires accurate measurements of average fiber size and variance of fiber diameters. However, it is not an easy task to obtain these properties because fiber size distribution varies to a large extent from point to point in a HEPA filter. In the present work, measurements of representative fiber size distribution from scanning electron micrographs of HEPA filter cross-section are performed and the particle penetrations are predicted with the measured fiber size distribution. They are compared with those from the conventional method (measurement from filter surfaces) and experimental data. As a result, even for filters with inhomogeneity factor delta(p)<1 by the conventional method, the present method gave delta(p)>1, suggesting that delta(p)<1 is caused by the failure in measurement for representative fiber size distribution. However, the improvement in prediction with more reliable filter properties is not satisfactory because the conventional filtration theory cannot account for the contribution of fine fibers properly. Introduction of bimodal fiber size distribution together with the measurement of fiber size distribution in a cross-section of a filter is found to give comparable prediction results with the conventional method without resorting the inhomogeneity factor of filter packing.

Consecutive pulse air jets are effective for the removal of fine particles from various surfaces. In the present work, the removal efficiencies of spherical particles from smooth flat surfaces are correlated by introducing three parameters (i. e., the fraction of particles removed by the first air jet blow, r(1), irremovable fraction of particles, ao, and the parameter related to the fraction of particles removed by each air jet blow, C'), and the dependencies of these parameters on F* (the ratio of drag force acting on a particle to van der Waals adhesion ford) are investigated. As a result, the removal efficiencies from smooth flat surfaces are successfully correlated by these parameters, and all of the parameters are well expressed as a single value function of F*. By applying these correlation equations to rough surfaces, it is found that another parameter to express the roughness of surface is necessary in predicting three parameters as a function of F*, although the removal efficiencies from rough surfaces are well correlated by the three parameters. Further, it is found that there is a particle size with a minimum removal efficiency for a given roughness of surface.

ABSTRACT Although ions in the atmosphere play important roles in nucleation and gas-phase chemical reactions, their dynamic behavior is not well understood. To study ion behavior, reliable techniques for ion generation and measurement are needed. In this work, we describe a stable unipolar ion generator using an Am source, and an improved version of the ion counter and Faraday cage electrometer by reducing deposition of ions in these instruments. The new ion generator produced unipolar ions at concentrations as high as 1 × 1013 m−3. The improved ion counter measured the ion concentration as low as 2.5 × 108 m−3 at a flow rate of 1.5 L/min.

The flow pattern of aerosol and sheath air in a cylindrical annulus of a Differential Mobility Analyzer (DMA) is critical to determine the classification performance of the DMA. In the present work, a new technique to check aerosol flow inside the DMA is proposed and the influences of aerosol flow distortion and broadening on the classification performance are investigated by means of the Tandem DMA method. As a result, it is found that (1) the annular flow inside the studied DMA is a fully developed laminar flow with a negligible mixing between aerosol and sheath air when the aerosol flow rate is less than 3 l/min and the sheath air flow rate is 17.5 l/min, (2) a larger width of aerosol entrance slit causes uneven distribution of aerosol flow in the circumferential direction, and (3) both the uneven distribution and broadening of the aerosol flow lead to a broader band of classified particle electrical mobility, as well as a shift of peak electrical mobility to a smaller range. These results suggest that aerosol flow inside a short-type DMA is more sensitive to the flow rates and its structure compared to the conventional TSI type DMA.

Particle formation of LMCS (low-molecular-weight poly-cyclo-dimethyl-siloxane) outgassed from silicone sealants by a corona-discharge ionizer was studied by measuring the number concentration and size distribution of formed particles as well as by qualitative analyses of formed particles with FT-IR (Fourier transformation infrared spectroscopy). Further, the influence of humidity and oxygen on the particle formation was investigated to find the reaction mechanisms. As a result, it was found that the LMCS is polymerized to form particles with two different reaction paths and that the LMCS is one of the major species that contribute to the formation of silicon-containing particles in cleanroom environments.

Separator-type HEPA filters are composed of elements which have square cross section bounded by two separator walls and partitioned by a filler medium. Therefore, it is possible to characterize pressure drop of a separator type air filter unit by studying the pressure drop of these filter elements.In the present work, the similarity law for the flow channels including a porous media was discussed and the dimensionless parameters which determine the pressure drop were derived. The dimensionless pressure drop was presented as a generalized-pressure drop diagram in terms of dimensionless parameters. Furthermore, the results of numerical analysis for the two-dimensional model filler were compared with those of experiments with two- and three- dimensional model filters. The prediction equation for optimum separator height, which is the most important factor for designing the filter unit, was presented as a function of filter media resistance and filter depth.

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 103 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.

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.