Separator inertial impaction

Inertial impaction is most widely applied for the characterization of inhalation systems. The principles of particle separation on the basis of inertial and drag forces have been well described for many different applications. Theoretical cut-off diameters (for particles with 50% collection efficiency) of impactors can be calculated on the basis of Stokes numbers for nozzles of a particular design [8,120]. Many different designs are available, but only a few are described in the United States and European Pharmacopoeia [121,122]. 

Filtration is a physical separation whereby particles are removed from the fluid and retained by the filters. Three basic collection mechanisms involving fibers are inertial impaction, interception, and diffusion. In collection by inertial impaction, the particles with large inertia deviate from the gas streamlines around the fiber collector and collide with the fiber collector. In collection by interception, the particles with small inertia nearly follow the streamline around the fiber collector and are partially or completely immersed in the boundary layer region. Subsequently, the particle velocity decreases and the particles graze the barrier and stop on the surface of the collector. Collection by diffusion is very important for fine particles. In this collection mechanism, particles with a zig-zag Brownian motion in the immediate vicinity of the collector are collected on the surface of the collector. The efficiency of collection by diffusion increases with decreasing size of particles and suspension flow rate. There are also several other collection mechanisms such as gravitational sedimentation, induced electrostatic precipitation, and van der Waals deposition their contributions in filtration may also be important in some processes. 

Entrainment can be separated from a gas stream with a variety of mechanisms, including gravity, inertial impaction, interception, centrifugal force, and Brownian motion. Separators can be classified according to mechanism, but it Is more useful to categorize them by construction type. Separators in common use include ... 

Vane impingement separator elements consist of parallel zig-zag plates or vanes with included collection pockets, simiiar to those shown in Figure 14-2. As an entrainment laden gas moves through the separator, the liquid particles are forced onto the vane surfaces by the inertial impaction mechanism. The resultant liquid film flows to the collection pockets, where it drains by gravity. 

Figure 6.3.1. Separation systems where the bulk flow is parallel to the direction offorce (a) elutriation (particle separation in liquids) (b) capillary electrophoresis (c) centrifugal elutriation (d) inertial impaction in particle filtration (e) distillation (flash/batch) (f) liquid extraction (separating funnel) (g) zone melting (h) normal freezing (i) cake filtration (j) ultri tration separation of proteins (dead-end) (k) batch cell reverse osmosis separation of brine (1) gas permeation.

Suspended solids are separated from fluids via three mechanisms inertial impaction, differential interception, and direct interception. 

Operation. The absolute separator is a multistage device utilizing all of the forces employed in mechanical separation—gravity, centrifugal force, inertial impaction, direct interception, and Brownian diffusion. 

An alternative to filtration is the use of inertial samplers, represented by impactors and cyclone separators (Figure 2a and Impaction, a method often used to size... 

Virtual impaction uses the principle of inertial separation, but the impaction plate is replaced by a zone of relatively stagnant air below the nozzle. The virtual surface formed by deflecting streamlines gives separation conditions similar to those in conventional impactors. Large particles travel straight through into the low-flow region,... 

The collection of the pyrolysis oils is difficult due to their tendency to form aerosols and also due to the volatile nature of many of the oil constituents. As the aerosols agglomerate into larger droplets, they can be removed by cyclonic separators. However, the submicron aerosols cannot be efficiently collected by cyclonic or inertial techniques, and collection by impact of the aerosols due to their Brownian or random motion must be utilized. A coalescing filter is relatively porous, but it contains a large surface area for the aerosol particles to impact by Brownian motion as they are swept through by the pyrolysis gases. Once the aerosol droplets impact the filter fibers, they are captured and coalesce into large drops that can flow down the fibers and be collected. 

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