Particle removal mechanism

The main forces liable to be exerted on fine particles are calculated in Table I. We can see from this table that the two main parameters that drive the particle adhesion-removal mechanisms are the van der Waals and electrostatic forces. 

The van der Waals forces [7,8], which link the particles to the substrates, can easily be calculated in the case of spherical particles  

A = Hamaker constant depending on the nature of the particle, the substrate, and the solution 

Calculation of the Forces Susceptible to be Exerted on a Fine Particle Deposited ON A Substrate (Case of Spherical Silicon Nitride Particles in Water at Room Temperature, Substrate Potential — 300V) 

Nature of forces Particle Forces, order of magnitude (N)  

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The ICRP deposition model estimates the fraction of inhaled material initially retained in each compartment (see Figure 3-2). The model was developed with five compartments (1) the anterior nasal passages (ET,) (2) all other extrathoracic airways (ET2) (posterior nasal passages, the naso- and oropharynx, and the larynx) (3) the bronchi (BB) (4) the bronchioles (bb) and (5) the alveolar interstitium (AI). Particles deposited in each of the regions may be removed and redistributed either upward into the respiratory tree or to the lymphatic system and blood by different particle removal mechanisms. 

FIGURE 16.10 A schematic diagram of the particle removal mechanism in SCI solution. 

Accumulation mode Particles in the transient nuclei mode can grow both by condensation of low-volatility materials and through coagulation, reaching the state of accumulation mode that consists of particles between ca. 100 nm and 2 pm in diameter. The accumulation mode is so called because particle removal mechanisms are the less efficient in this regime, causing particle to be accumulated. 

Smaller pore size microfilters in single-pass systems which have pore sizes small enough to remove some vimses by size exclusion have been examined (26,37,38). Minimum levels of vims removal can be estabhshed for these systems if fluid and process conditions are employed which minimize removal of viral particles by mechanisms other than size selection. 

A PVDF membrane filter has been shown to remove >10 particles of vims for vimses >50 nm independent of fluid type (8). Vimses smaller than 50 nm are not removed as efficientiy but are removed in a predictable manner which correlates to the vims particle size. The chemistry of the suspending fluid affects titer reduction for vimses <50 nm owing to other removal mechanisms, such as adsorption, coming into play. The effects of these other mechanisms can be minimized by using filtration conditions that minimize adsorption. 

The size of particles removed by such filters is less than the size of the passages. The mechanism of removal includes adsorption (qv) of the impurities at the interface between the media and the water either by specific chemical or van der Waals attractions or by electrostatic interaction when the medium particles have surface charges opposite to those on the impurities to be removed. 

Condensation Scrubbing The collection efficiency of scrubbing can be increased by the simultaneous condensation of water vapor from the gas stream. Water-vapor condensation assists in particle removal by two entirely different mechanisms. One is the deposition of particles on cold-water droplets or other surfaces as the result of... 

Table 13.1 covers general information for different particulates, liquids in gas, typical particles and gas dispersoids, behavior of particles in the human body, charging mechanisms, principles of particle size analysis, methods for particle size analysis, and an estimation of the general collection efficiency of available commercial particle removal equipment. 

That is, the removal of spherical particles from a flat surface is determined by the magnitude of the wall shear stress, x0. Visser (1) also claims that since the removal mechanism is unknown, it is not possible to relate the Fh (tangential force) to the Fa (adhesive force) on theoretical grounds. Therefore, he assumes that the tangential force required for particle release is proportional to the adhesive force. 

Kim W, Kim TH, Choi J, Kim HY (2009) Mechanism of particle removal by megasonic waves. Appl Phys Lett 94 081908 (3 pages)... 

Condensation Scrubbing The collection efficiency of scrubbing can be increased by the simultaneous condensation of water vapor from the gas stream. Water-vapor condensation assists in particle removal by two entirely different mechanisms. One is the deposition of particles on cold-water droplets or other surfaces as the result of Stefan flow. The other is the condensation of water vapor on particles as nuclei, which enlarges the particles and makes them more readily collected by inertial deposition on droplets. Both mechanisms can operate simultaneously. However, for the buildup of particles by condensation to be effective, there must be adequate time for the particles to grow substantially before the principal gas-liquid-contacting operation takes... 

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