K.W. Lee

Log-Normally Preserving Size Distribution for Brownian Coagulation in the Free-Molecule Regime

Coagulation of aerosol particles in the free-molecule regime has been studied theoretically by converting the governing partial integrodifferential equation into a set of two ordinary differential equations. The approach assumes that the size distribution of an aerosol attains or can at least be represented by a time-dependent log-normal distribution function during the coagulation process. The calculations have been performed and the results found to be in good agreement with results for previous theories. In addition, the following asymptotic size distribution function is found as an alternative solution for the self-preserving particle size distribution function for Brownian coagulation of an aerosol in the free-molecule regime: , where n is the particle size distribution function, N ∞ is the total number of particles, r is the particle radius, and rg∞ is the geometric mean particle radius. In terms of the parameters used by the self-preserving size distribution theory, the proposed distribution is wri...

The log-normal size distribution theory of brownian aerosol coagulation for the entire particle size range : part I analytical solution using the harmonic mean coagulation kernel

Abstract Brownian aerosol coagulation was studied theoretically using the moment method of log-normal size distribution functions. An analytic solution to the size distribution of a coagulating aerosol was derived. In order to cover the entire size range the harmonic mean of the near-continuum and the free-molecule coagulation coefficient were applied. Therefore, the analytic solution is valid for the entire particle size range, i.e. covering from the free-molecule regime, via both the transition and the near-continuum regimes, to the continuum regime. The present work represents the first analytical solution to the Brownian aerosol coagulation problem that addresses the entire particle size range.

Coagulation Rate of Polydisperse Particles

The coagulation rate of suspended particles is studied analytically, taking into account the effects of both the particle size and the size spread. The log normal function was utilized for represen...

Experimental study on small cyclones operating at high flowrates

A new set of experimental data on the particle collection efficiency of small cyclones operating at high flowrates is reported. Seven different cyclones were studied systematically covering a flowrate range 60–110 l min-1 and a particle size range 0.026–3.6 μm. Special emphasis was given to the effects of the cylinder height and of the exit tube length on the particle collection efficiency. The length ratios of the cylinder height and exit tube length to the cyclone body diameter were varied from 0.75 to 4.5 and from 0.5 to 1.5, respectively. The experimental results suggest that the flowrate plays a significant role in cyclone collection efficiency. High flowrate can help to collect fine particles. As the cylinder height is increased, the collection efficiency increases. However, when the cylinder height is increased excessively, the collection efficiency appears to decrease to certain extent. An optimized exit tube length was also observed. Pressure drop decreased substantially either as the cylinder height became longer or as the exit tube length became shorter. It was also found that the difference between the cyclone cylinder height and the exit tube length affects the particle collection characteristics significantly.

Experimental study of particle collection by small cyclones

A new set of experimental data on the particle collection characteristics of small cyclones is reported. The collection efficiency for particles ranging from 2 to 10 μm in diameter was measured systematically for nine cyclones at flow rates ranging from 8.8 to 18.4 L/min. Special emphasis was given to the effects of the exit tube size and of the cyclone body size on the particle collection efficiency. The size ratio of the exit tube to the cyclone body was varied from 0.24 to 0.80. The experimental results show that the stiffness of the particle collection cutoff with size does not change noticeably with a change in the cyclone body size while operation of a cyclone at a low flow rate can cause the particle collection characteristics to become less stiff. It was also found that the exit tube diameter influences the particle collection efficiency substantially, with results showing that as the exit tube size is decreased, the collection efficiency increases. A large cyclone body size increases the efficien...

Effects of cone dimension on cyclone performance

The effects of cone dimension on cyclone performance characteristics were investigated in this study. Collection efficiencies for three cyclones with different cone bottom diameters were measured as a function of particle size and flow rate. The measurement results suggest that flow rate strongly influenced the efficiency values and the sharpness of the efficiency curves. Cone size, on the other hand, only has significant effect on collection efficiency. When the cone opening is larger than the gas outlet diameter, reduction in cone size results in higher collection efficiency without significantly increasing the pressure drop. Experimental data were compared with the predictions of Barths theory, Leith and Lichts theory, and Iozia and Leiths logistic method. Results show that only Barths theory and the logistic method of Iozia and Leith predict the efficiency curve reasonably well. However, none of the three theories correctly and sufficiently takes into account the effects of cone size.

DEPOSITION OF PARTICLES IN TURBULENT PIPE FLOWS

Abstract Deposition rates of aerosol particles onto pipe walls under turbulent flow conditions were measured. Dioctyl phthalate (DOP) aerosols of six different sizes ranging from 0.035 to 1.3 μm were used in air flows whose Reynolds numbers were controlled at selected values between 1800 and 15,600. The turbulent inertial impaction, transition, and turbulent diffusion regimes were covered. The measured results show that the theory by Wells and Chamberlain (1967, Brit. J. appl. Phys.19, 1793) predicts deposition by diffusion in turbulent flows reasonably well, while the theory of Friedlander and Johnstone (1957, Ind. Engr. Chem.49, 1151) is suitable for correlating the data for deposition by inertial impaction. However, these theories alone were not satisfactory for estimating deposition rates in the neighborhood of the minimum aerosol deposition regime where both Brownian diffusional and inertial deposition mechanisms operate simultaneously.

An analytic solution to free molecule aerosol coagulation

The purpose of this note is to extend the study of Lee et al. (1984) to develop an approximate solution in the analytic form which gives the size distribution of a coagulating aerosol in the free molecule regime for the entire time period of coagulation

Characteristics of the collection efficiency for a double inlet cyclone with clean air

Abstract Two single inlet cyclones and a double inlet cyclone were designed and fabricated to evaluate, and compare, their collection efficiencies. Two single inlet cyclones had different inlet sizes and vortex finder diameters. The double inlet cyclone had two inlet parts that divided the cyclone inlet in two. Clean air was introduced to the inlet near the cyclone wall, and particle-laden air was introduced to the inlet away from the cyclone wall. This double inlet made the clean air swirl in the region near the vortex finder, and the particle-laden air swirl in the region close to cyclone wall. The performance of the double inlet cyclone was evaluated at various clean air flow rates, keeping the particle-laden air flow rate constant. The collection efficiency of the double inlet cyclone was found to be 5–15% greater than that of the single inlet cyclone with the same inlet size and vortex finder diameter. As the flow rate of clean air was increased, the collection efficiency increased. This result indicates the possibility of achieving higher collection efficiencies with a double inlet cyclone.

Maximum penetration of aerosol particles in granular bed filters

Abstract The size of the aerosol particles that most effectively penetrate a granular bed, and the corresponding minimum collection efficiency have been predicted by considering Brownian diffusion, particle interception and gravitational sedimentation as controlling aerosol deposition mechanisms. The results show that the most penetrating particle size for a granular bed filter exists as a result of either the Brownian diffusion mechanism combined with gravitation or Brownian diffusion with the interceptional mechanism. In the former case, the most penetrating particle size shifts to the larger size range as either air velocity or granule size increases. In the latter case, that size is found to shift to the smaller size range under the identical conditions. Where all these three mechanisms are operative to about equal extent, the most penetrating particle size reaches a maximum. Regardless of such shifts of the most penetrating particle size, the corresponding minimum efficiency of a granule bed filter is found to decrease with increasing air velocity or granule size. The calculated results have been compared with existing experimental data and excellent agreement has been obtained.