Particle Deposition Enhancement Research Articles

Electrostatic deposition of a moving charged aerosol cloud onto a conducting sphere

Transient electrostatic deposition of particles from a monodisperse aerosol cloud moving past a perfectly conducting spherical collector is studied by means of direct numerical simulation. Two ideal cases of electrically grounded and insulated spheres are considered. In the case of a grounded sphere the Coulomb interaction between moving charged aerosol cloud and the induced electrical charges on the sphere causes significant enhancement of particle deposition. Important characteristics of the process, such as rates of deposition, the deposited mass, and typical cloud configurations for various values of dimensionless time and parameter of electrostatic interaction are found. It is shown that charging of the insulated target by arriving aerosol particles and electrostatic expansion of the cloud due to reciprocal repulsion of the charged particles can substantially impede the deposition process.

Enhanced deposition of particles under attractive double-layer forces

The kinetics of Brownian particle deposition from flowing suspensions in the vicinity of a stagnation point (rotating disk, spherical, cylindrical, and impinging jet collectors) was studied theoretically and experimentally. On the basis of the numerical solutions of governing transport equations a considerable enhancement of particle deposition was predicted for particle and collectors bearing opposite surface charge (zeta potentials). The initial deposition rate of particles can be increased by many times when decreasing the ionic strength of the suspension to the value 10 −5–10 −6 M. This effect, which we shall refer to as the reverse salt effect, is completely opposite to what one commonly observed for equally charged particle and collector surfaces (as well as in coagulation kinetic studies). These theoretical predictions were confirmed quantitatively by the direct microscope observation method using mica collector (modified by chemisorption of silano compounds) and a monodisperse suspension of submicrometer latex particles (negatively charged). The experiments also furnished a direct evidence of the coupling between macroscopic hydrodynamic flow and the microscopic colloid forces and proved that the asymmetric double-layer dynamics cannot be properly described by the constant surface charge boundary conditions.

Enhancement of particle deposition by flow-limiting segments in humans.

Severe chronic obstructive pulmonary disease is associated with central deposition of inhaled aerosols. This pattern may be due to functional narrowing of the large airways during expiration at flow-limiting segments (FLS). Using a gamma camera and 2.5-micron particles, we compared the pattern of aerosol deposition following quiet breathing with that after a controlled forced expiration (cough) when FLS are known to form in central airways. Lung size measurement by 133Xe allowed construction of regions of interest over the central airways and lung periphery. Deposition in these regions was normalized for area and lung thickness and expressed as a central-to-peripheral (C/P) ratio. In addition, using right-angle light scattering, the fraction of inhaled particles deposited with each breath (DF) was determined. During control studies, airflow and tidal volume were continuously monitored to insure that tidal loops were well below the maximum expiratory flow-volume (MEFV) curve. To create dynamic compression, cough was used to generate a partial MEFV curve, while inspiratory flow, tidal volume, and functional residual capacity were maintained close to quiet breathing. With cough, C/P ratios increased markedly from 1.04 +/- 0.18 to 2.21 +/- 0.61 (P less than 0.01, n = 6). DF for the lung and airways did not significantly change (0.43 +/- 0.11 to 0.45 +/- 0.09, P = NS). The greater enhancement of regional deposition in the central airways with deposition unchanged over the whole lung demonstrates that, during cough, peripheral deposition is actually reduced when compared with quiet breathing. We conclude that dynamic compression at FLS can be an important factor in the central deposition of inhaled particles.