Kikuo Okuyama

Development of a mixing type condensation nucleus counter

Abstract A new mixing type CNC, the principle of which is based upon that of fog formation in the atmosphere caused by mixing of warm saturated air with cold air, has been developed. The principle of the CNC was examined from the viewpoints of counting efficiency of ultrafine particles and the droplet size after condensational growth as a function of particle number concentration and the quantity of condensable vapor; theory and experiment were found to agree. The CNC is capable of size analysis where the Kelvin equivalent diameter is detected. An ultrafine aerosol generator, having a liquid nitrogen quenching system, has been developed to obtain fairly monodisperse aerosol particles down to about 8 nm.

Condensational Growth of Ultrafine Aerosol Particles in a New Particle Size Magnifier

A new particle size magnifier (PSM) has been manufactured. In order to evaluate the performance of the PSM, the condensational growth of ultrafine aerosol particles in a supersaturated dibutyl phthalate vapor-air mixture is investigated theoretically and experimentally. First, the supersaturation ratio, the condensable DBP vapor content, and the critical size of the particle that will grow in the PSM are calculated for the mixing of hot air containing the DBP vapor with normal-temperature vapor-free air. Then the time dependence of the droplet radius during condensational growth is evaluated by numerically solving the basic equation under various conditions. From the results it is found that at higher particle number concentrations, the final droplet radii can be determined by the particle number concentration and the condensable DBP vapor content, but that at lower concentrations the particle growth can be approximated by the growth of the isolated droplet. Finally, size distributions of grown DBP drople...

Particle loss of aerosols with particle diameters between 6 and 2000 nm in stirred tank

Abstract Deposition loss of aerosol particles in a stirred tank has been studied experimentally by observing the time-dependent changes in particle number concentration for various intensities of stirring. The stirred tank used in this study is a standard baffled tank with six-bladed turbine impeller or three-bladed propeller, and the aerosol particles used are monodisperse uncharged NaCl, DEHS (diethylhexyl sebacate), and polystyrene latex particles. The experimental results have shown the clear dependence of the deposition rate on particle size and turbulent intensity of stirring, and also shown that for a given intensity there exists the particle size at which the deposition rate constant becomes minimum. From the comparison of the experimental results with the representative theory of Crump and Seinfeld (J. Aerosol Sci. 12, 405, 1981), it has been found that the experimental deposition rates can be explained well by their theory where the eddy diffusivity near wall is assumed to be proportional to 2.7th power of the distance from the wall. And the equation for predicting the minimum deposition velocity under a given stirring speed has been derived.

Response characteristics for four different condensation nucleus counters to particles in the 3–50 nm diameter range

Abstract The response characteristics of four condensation nucleus counters (CNCs) to monodisperse sodium chloride aerosol particles in the 3–50 nm diameter range are compared with concentrations that were measured with an aerosol electrometer. Measurements were conducted in a workshop that was held at the University of Minnesota Particle Technology Laboratory, 24–28 September 1984. The CNCs that were investigated included a variable expansion ratio CNC (Niessner et al ., 1984), a commercial steady flow CNC (TSI, Inc., Model 3020), a modified version of the TSI Model 3020 CNC (Stolzenburg and McMurry, 1984), and a mixing type CNC (Kousaka et al ., 1982). The latter two instruments were specifically designed for accurate measurements of aerosol concentrations for particles smaller than 10 nm. For particles of 24 and 50 nm, responses of all CNCs were within about ± 10% of values determined with the aerosol electrometer. For particles smaller than 10–20 nm, concentrations measured with the electrometer exceeded those measured by the CNCs. For 3 nm NaCl particles, average CNC counting efficiencies (CNC response/electrometer response) were 0.06 ± 0.03 (TSI, Inc. Model 3020), 0.60 ± 0.18 (Kousaka et al. mixing-type CNC) and 0.83 ± 0.17 (Stolzenburg and McMurry modified Model 3020 CNC). The size-dependent counting efficiency of the variable expansion CNC was similar to that for the TSI CNC. These data indicate that counting efficiencies for very small particles depend substantially on instrument design.

Homogeneous and heterogeneous nucleation in a laminar flow aerosol generator

The formation of aerosol particles by homogeneous and heterogeneous nucleation has been studied experimentally using a laminar flow aerosol generator. Dry gas (N2 or air) saturated with dibutylphthalate (DBP), either particle-free or containing an ultrafine monodisperse aerosol, was cooled well below the saturation temperature causing the highly supersaturated vapor to nucleate. The resulting particle number concentrations were observed under various conditions of the gas stream and properties of the introduced foreign condensation nuclei. The dependence of the nucleation rate on the vapor concentration, cooling rate, and seed aerosol concentration was studied. Comparisons of the measured number concentrations with predictions based on the model of A. J. Pesthy, R. C. Flagan, and J. H. Seinfeld (J. Colloid Interface Sci. 91, 525 (1981)) showed good qualitative agreement when the classical homogeneous nucleation rates were enhanced by a factor of 105–107. The laminar flow aerosol generator is found to be an effective system for the study of the influence of foreign particles on the rate of homogeneous nucleation of a vapor.

Change in size distribution of ultrafine aerosol particles undergoing Brownian coagulation

Abstract Brownian coagulation in the free molecular and transition regimes has been studied. In the experiment, highly concentrated NaCl, ZnCl2, and Ag aerosol particles having geometric mean diameter of 5–40 nm and geometric standard deviation around 1.4 were passed through a metal pipe of 2.0 cm diameter in laminar state. At the inlet and the outlet of the coagulation pipe, the particle size distributions were measured by means of a differential mobility analyzer combined with a CNC and the particle number concentrations were counted independently by an ultramicroscopic system after enlarging their size in a particle size magnifier. In theoretical calculation, the coagulation rate function proposed by Fuchs was used, and the pupulation balance equation for simultaneous Brownian coagulation and diffusive deposition of aerosols in laminar pipe flow was numerically solved. It was found that the experimental results deviated from the theoretical calculation with the decrease in the particle size, that is, the enhancement of coagulation rate was observed. This will be caused by the van der Waals attractive force, which was qualitatively explained from the Marlows theory.

Homogeneous Nucleation by Continuous Mixing of High Temperature Vapor with Room Temperature Gas

The formation of aerosol particles by homogeneous nucleation in a supersaturated vapor has been studied experimentally and theoretically. In the laboratory, a particle-free gas at room temperature is continuously mixed with a high-temperature gas containing dibutylphthalate vapor in a new device for the study of aerosol nucleation called a particle size magnifier. A highly supersaturated vapor is rapidly formed in the mixing zone of the particle size magnifier, and the resulting number concentrations of aerosol particles are measured under various temperatures, mixing ratios, and mixing methods. Measured number concentrations are compared with those predicted by the classical and Lothe-Pound nucleation theories. The measured concentrations lie between the predictions of the two theories, and the trends with temperature and saturation ratio are consistent with either nucleation theory, provided vapor depletion is considered.

Bipolar Charging of Ultrafine Aerosol Particles

The stationary bipolar charging characteristics of aerosol particles in the size range between 4.5 and 40 nm have been studied using a new technique whereby the particles neutralized by a 241Am radioactive source are enlarged and directly observed in an electric field. The number ratio of charged particles to total particles obtained in this study was found to deviate from the charge distribution obtained from Boltzmanns law and to agree well with that calculated with the bipolar charging theory of Fuchs using his values for the ion properties. The ratio of positively charged to negatively charged particles was found to be approximately 0.35:0.65. *Work performed at the Department of Chemical Engineering, University of Osaka Prefecture, Sakai, Japan.

Facilitated aerosol sizing using the differential mobility analyzer

The electrostatic size analysis of polydisperse aerosols using a differential mobility analyzer (DMA) has been studied from the following two standpoints: (1) the faster measurement of electrical mobility distribution, arid (2) the correction of particle loss by Brownian diffusion in the data inversion, fn electrical mobility measurements, the number of mobility channels in a scan of the full mobility range is decreased and the full electrical mobility distribution is estimated by interpolation with a spline fitting. The correction of the Brownian diffusive losses of particles in the DMA including a neutralizer are combined with the data inversion method in order to evaluate the size distribution of aerosols unaffected by the particle loss. The reliability of the corrected data inversion method is confirmed by the experiment, and the particle size distribution of an aerosol is determined within several minutes by means of a faster scanning technique. This work was performed at the Department of Chemical E...

Binary nucleation of methanesulfonic acid and water

Abstract A continuous-flow, mixing-type device for the study of binary nucleation phenomena has been developed and applied to the methanesulfonic acid-water system. Experimental measurements confirm the formation of particles from the binary gas at partial pressures of water vapor and acid vapor below saturation levels. Although trends in the data agree with the predictions of binary nucleation theory, the observed number concentrations are not well predicted using macroscopic values of the solution properties.