Particle trap impactor

So far, the value of 0.24 is used for the Stkso of particle trap impactors and cup impactors (Kim et al., 1998, 2002). The acceleration nozzle diameter, D of System I, 2.6 mm, is determined from the Stkso, and that of System II, 2.2 mm, is decided to increase collection 

Design parameters and test conditions of a particle trap impacta- 

---

Cascade impactors are instruments which have been extensively used for sampling and separating airborne particles to determine the aerodynamic size classification of aerosol particles. There are three kinds of cascade impactors inertial impactors, virtual impactors and particle trap impactors. 

Even though inertial and virtual impactors have been widely used for aerosol collection and separation, particle trap impactors have not been used extensively. So far, studies on particle trap impactors were not carried out sufficiently. In addition, most particle trap impactors employ the design of inertial impactors for their design parameters, though actually the design of particle trap impactors is different from that of inertial impactors. Therefore, there still remains the necessity for study of the accurate design parameters for particle trap impactors. 

A particle trap impactor with three different sets of geometrical parameters is presented in a schematic diagram in Figure 6.17. The design of the particle trap impactor is based on the particle cup (trap) impactor configuration of Kim et al. (2002). The sampling flow rates of Systems I and n are set at 5 Lmin , and the acceleration nozzle diameter is calculated from the Stokes number, Stk. The Stokes number of a particle having a 50% probability of separation, Stkso, is defined as follows ... 

An experimental set-up used for characterising a particle trap impactor is shown in Figure 6.18. Figure 6.19 shows the penetration efficiency curves for the different nozzle diameters. Systems I and II have the acceleration nozzle diameter of 2.6 and 2.2 mm, respectively, while the sampling flow rates and S/D values of both systems are the same 5 Lmin and 1.3, respectively. Penetration curves are expressed as a function of the aerodynamic particle diameter (a) and the square root of the Stokes number (b), respectively. 

Figure 4. Qualitative fluorescence analysis of a 5 n fly ash particle trapped on the first stage of the Cassella cascade impactor used to sample the precipitator inlet...

Particles are commonly retained on membrane filters or impactors. Gaseous components and volatile organic compounds (VOCs) are collected by trapping, either cryogenically (for the most volatile substances) or on sorbents of increasing retentivity (for the less volatile ones). 

A cascade impactor consists of a series of orifices, of decreasing opening size, which lie ahead of collecting plates (see Figure 2.22). For each orifice size, particles that are too large to remain with the gas stream are deposited onto the collection plates. With each subsequent stage, smaller and smaller particles are trapped and collected. Since the collection is due to sedimentation, the results are usually reported in terms of equivalent aerodynamic diameter. Since each size fraction is collected on a separate collection plate, they are available for individual chemical analysis. Cascade impactors are applicable to the collection and classification of particles down to about 10 nm and up to about 25 pm (aerodynamic diameter) [128,129]. 

Impingers and impactors include wet scrubbers as an example, which remove fine aerosol particles and/or droplets by trapping them in liquid droplets that can be separated from the gas stream. The droplets with their trapped aerosol materials are usually separated using a mist eliminator, which usually involves impaction of the droplets on packing materials of various kinds, such as porous... 

We must note that the property of tackiness is used to trap dust particles in self-cleaning oil filters, in coarse dust filters for motor vehicles, in Rank filters made of metal screen, and on the precipitation plates in konimeters, impactors, and other such devices. Moreover, adhesion to a tacky base may be used in investigating dust content and dust compositions, particularly in trapping dust in the ground layer of the atmosphere. 

Impactor samplers, which permit a broader range of measurable particulate size distributions, are constructed so that air entering at high flow rates encounters a series of trapping surfaces and particles are trapped based on size. First trapped are the coarsest particles followed sequentially by smaller and smaller fractions. The cascade samplers typically allow fractionations within narrow ranges, such as 0.01—0.1 (im (Dzubay et al., 1976). 

In view of the absence of published data regarding the mechanism underlying the behavior of a tacky layer in the capture of dust, we must at present confine attention to qualitative considerations. It should be noted that the property of tackiness is used for the trapping of dust particles in self-cleaning oil filters, rou -cleaning automobile antidust filters. Rank filters made of metallic mesh, settling plates in konimeters, impactors, and similar apparatus [162]. In addition to this, adhesion to... 

---