Particle aerodynamic

Impactors utilize aerodynamic forces to separate the various particle size classes. This is consistent with the particles aerodynamic diameter. The operation... 

Particle aerodynamic diameter The diameter of a sphere of density 1 g cm that has the same terminal velocity due to gravitational force in still air at set conditions of temperature, pressure, and relative humidity as the particle in question. 

Separation in these devices known as winnowing machines [3], is achieved due to the difference between trajectories of coarse and fine particles in the separation zone (Fig. lb). Their operation and efficiency are strongly affected by the stochastic factors of the process, in particular by uncertainties in feeding and particles aerodynamic interactions. In most cases coarse particles prevent proper classification of fines. Separation efficiency of these devices is usually low. They are normally used for separation of solid particles according to densities (e.g. grain from peel), rather than by size. Sometimes crossflow separation in horizontal streams is used in combination with other separation principles. 

Fig. 3. Force balance on a particle aerodynamic due to air flow (up) and gravity (down).

Electrical Single Particle Aerodynamic Relaxation Time (E-SPART) Analyzer simultaneously measures size in the range from submicron to 100 pm and particle charge distribution from zero to saturation levels [177,178]. 

Mazumder, M.K. E-spart analyzer its performance and applications to powder and particle technology processes. KONA 1993, 11, 105-118, KONA is produced by the Hosokawa Micron International Inc., which Markets the E-SPART Analyzer Literature is available from Micron Powder Systems (a member of the Hosokawa Micron group), 10 Chatham Rd., Summit, NJ 07901. (The term SPART Analyzer stands for Single Particle Aerodynamic Relaxation Time analyzer). 

Major advantage area Established, proven Good particle aerodynamics Pure non-cohesive powders... 

Four, five and six rings PAHs are mainly distributed into particle size smaller than 2,0 pm. The concentration of high molecular weight PAH increased while the particle aerodynamic diameter decreased. 

Three primary mechanisms govern the deposition of aerosols in the respiratory tract inertial impaction, sedimentation, and diffusion (Fig. 7). Early work by Landahl and coworkers showed that both sedimentation and inertial impaction in the mouth, throat, and lungs uniquely depend on the particle aerodynamic diameter [220], Deposition by diffiisional transport is independent of particle density and limited primarily to particles with geometric diameters smaller than 0.5 p,m [221],... 

Figure 8 Particle deposition in the human respiratory tract as a function of particle aerodynamic diameter. (Reprinted from Ref. 226. Courtesy of Medical Physics Publishing.)...

Figure 7. Deposition Velocity vs. Particle Aerodynamic Diameter, Type Surrogate Surface Filter Paper (23-28).

In the applications of gas-solid flows, measurements of particle mass fluxes, particle concentrations, gas and particle velocities, and particle aerodynamic size distributions are of utmost interest. The local particle mass flux is typically determined using the isokinetic sampling method as the first principle. With the particle velocity determined, the isokinetic sampling can also be used to directly measure the concentrations of airborne particles. For flows with extremely tiny particles such as aerosols, the particle velocity can be approximated as the same as the flow velocity. Otherwise, the particle velocity needs to be measured independently due to the slip effect between phases. In most applications of gas-solid flows, particles are polydispersed. Determination of particle size distribution hence becomes important. One typical instrument for the measurement of particle aerodynamic size distribution of particles is cascade impactor or cascade sampler. In this chapter, basic principles, applications, design and operation considerations of isokinetic sampling and cascade impaction are introduced. 

The ICRP 66 model employs 10 input parameters for the determination of regional deposition fraction. These input parameters were varied according to their characteristic distributions, in an effort to perform uncertainty analysis of regional deposition fraction. The parameter particle aerodynamic diameter d (Table 27.1), is dependent on the AMAD distribution of the aerosol, and cannot be varied with respect to the uncertainty analysis. The remaining nine parameters (Table 27.1) are independent and are varied to determine the uncertainty in regional deposition fraction estimates. The resulting estimates are fitted to known distributions and described by their characteristic parameters. Statistical analyses were performed on input... 

Regardless of the method used to generate the aerosol, efficient pulmonary deposition of the active agent is critically dependent on the aerodynamic diameter of the inhaled particle. Aerodynamic diameter is the physical property of a particle, which defines how it will behave in an airstream, and depends on the particle geometric size, density, and shape. An in-depth discnssion of how particle shape affects aerodynamic diameter is beyond the scope of this review therefore, the cited examples will assume a spherical particle. 

As a negative control, an aerosol bolus of monodisperse, radiolabeled particles (aerodynamic diameter d, 3 pm) was injected at the beginning of an inhalation. Then, the particles were transported deep into the lungs and were deposited in the alveolar region. The measurements showed that less than 5% of the particles were cleared within 24 hr and the retention decreased with a half-time of about 100 days. This was also shown by other investigators, who found that particles were deposited mainly in the alveolar region (2,38,39). 

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