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Spheres aerodynamically equivalent

Besides mass concentration, atmospheric particles are often characterized by their size distribution. Aerosols are typically sized in terms of the aerodynamic equivalent diameter (dae) of the particle, usually expressed in micrometer (pm) or nanometer (nm) (Mark, 1998). Atmospheric particles are usually nonspherical and with unknown density. Therefore, the r/ae of a particle is usually defined as the diameter of an equivalent unit density sphere (p = 1 gctrf3) having the same terminal velocity as the particle in question (Mark, 1998 Seinfeld and Pandis, 1998). [Pg.453]

The seas may also act as a receptor for depositing aerosol. Deposition velocities of particles to the sea are a function of particle size, density, and shape, as well as the state of the sea. Experimental determination of aerosol deposition velocities to the sea is almost impossible and has to rely upon data derived from wind tunnel studies and theoretical models. The results from two such models appear in Figure 4, in which particle size is expressed as aerodynamic diameter, or the diameter of an aero-dynamically equivalent sphere of unit specific gravity.If the airborne concentration in size fraction of diameter d is c then... [Pg.324]

The aerodynamic diameter dj, is the diameter of spheres of unit density po, which reach the same velocity as nonspherical particles of density p in the air stream Cd Re) is calculated for calibration particles of diameter dp, and Cd(i e, cp) is calculated for particles with diameter dv and sphericity 9. Sphericity is defined as the ratio of the surface area of a sphere with equivalent volume to the actual surface area of the particle determined, for example, by means of specific surface area measurements (24). The aerodynamic shape factor X is defined as the ratio of the drag force on a particle to the drag force on the particle volume-equivalent sphere at the same velocity. For the Stokesian flow regime and spherical particles (9 = 1, X drag... [Pg.267]

As with most questions on particle size, the answer is very dependent on the definition used and the experimental technique. For a dynamic aerosol cloud, the correct definition is the aerodynamic particle size, which is the diameter of an equivalent sphere of unit density. An equivalent sphere is a conventional assumption in particle sizing, but for the aerodynamic size, the density is included to account for the momentum of the particle, i.e., both mass and velocity are important. The technique chosen for measurement must include these parameters, and impaction is the normally chosen technique, which also reflects the major deposition mechanism in the lung. A schematic of an impaction plate is given in Figure 10.3. [Pg.358]

Equivalent aerodynamic diameter The diameter of a standard density sphere that would settle at the same rate as the actual particle. [Pg.252]

The aerodynamic diameter is one of the most common equivalent diameters. It can be defined as the diameter of a unit den.sity sphere with the same terminal settling velocity as the particle being measured. The aerodynamic diameter is commonly used to describe the mt)lioii of particles in collection devices such as cyclone separators and impactors. However, in shear flows, the motion of irregular particles may not be characterized accurately by the equivalent diameter alone because of the complex rotational and translational motion of inegular particles compared with spheres. That is, the path of the irregular particle may not follow that of a particle of the same aerodynamic diameter. It is of course possible that there may be a. sphere of a certain diameter and unit density that deposits at the same point this could be an average point of deposition because of the effects of turbulence or the. stochastic behavior of irregular particles. [Pg.5]

For larger particles or nanoparticle aggregates, SMPS measurements can be coupled with an aerodynamic particle sizer (APS). For spherical particles, it is easy to relate the measured diameters from the SMPS and APS because no corrections need to be made for shape and volume, but for irregularly shaped particles the APS reports an aerodynamic diameter. Da, by comparing the settling velocity to a spherical particle with a density of 1 g cm to compute the particle size. A volume equivalent diameter, D g, which is defined as the volume of a sphere with the same volume as a particle with an irregular shape, is used to relate the aerodynamic diameter from the APS with mobility diameter, D , from the SMPS (46) ... [Pg.693]

There are many ways to describe the size of an aerosol particle. For example it may be described by its longest dimension or by a sphere of equivalent volume. It may be described by its light scattering properties or by the way it behaves in an airstream. In a very real sense there is no such thing as the correct size or diameter of an aerosol particle. There are as many correct diameters as there are ways of measuring it, and it is up to the researcher to measure a size parameter relevant to the particular application under investigation. From a deposition perspective, it is the inertial behavior of the particle in an airstream that defines how and where it will deposit (Chap. 2). This characteristic diameter is known as the aerodynamic diameter and is the characteristic diameter that is normally... [Pg.107]

The aerodynamic behaviour of aerosol particles depends on their diameter, density and shape. To compare the behavioiu of particles that have different properties with each other, the aerodynamic diameter (Da) has been introduced, which standardises for particle shape and density. By definition the aerodynamic diameter of a particle is the diameter of a sphere with unit density having the same terminal settling velocity as the particle in consideratimi. Only for aqueous droplets with a spherical shape and unit density the aerodynamic diameter equals the geometric diameter. For non-spherical particles, the aerodynamic diameter can be expressed in terms of equivalent volume diameter (De), particle shape factor (x) and particle density (p) (see definitions) Da = De.(p/x)° ... [Pg.101]

Actual diameters are difficult to estabhsh therefore, an equivalent aerodynamic diameter (e.a.d.) is used. The e.ad. is the diameter of a small sphere with a density of 1 g/ml which settles at the same speed as a particle. [Pg.307]

Another way of looking at this is to talk about equivalent aerodynamic diameter (e. a.d.) . What we mean is that if a parhcle has an e.a.d. of 7 micrometres it falls at the same speed as a 7 micrometre sphere with a density of 1 g/ml. This approach means that we get away from size and shape and look at what the parhcle does that is, how easily does it sediment or fall out. Experiments have shown that in dust which reaches the alveoli, virtually no parhcle has an e.a.d. of more than 7 nhcrometres - 50% of particles with e.a.d. of 5 micrometres get that far, and nearly 100% of parhcles with e.a.d. of 0.1 micrometer or less do so. [Pg.414]

You may have read that it is asbestos fibres of up to 3 micrometer real diameter which pose a threat to the lower lung. This is so because an asbestos fibre (a fibre is a particle at least three times as long as wide) of 3 micrometer diameter falls out at a speed the same as a spherical particle of ordinary dust with an equivalent aerodynamic (not real) diameter of 7 micrometers (it is not a true sphere but is called spherical because it is very roughly the same diameter whichever way you measure it). [Pg.415]


See other pages where Spheres aerodynamically equivalent is mentioned: [Pg.482]    [Pg.774]    [Pg.777]    [Pg.482]    [Pg.774]    [Pg.777]    [Pg.97]    [Pg.166]    [Pg.203]    [Pg.192]    [Pg.2]    [Pg.482]    [Pg.59]    [Pg.300]    [Pg.35]    [Pg.192]    [Pg.87]    [Pg.285]    [Pg.425]    [Pg.30]    [Pg.295]    [Pg.109]    [Pg.157]    [Pg.234]    [Pg.450]   
See also in sourсe #XX -- [ Pg.777 ]




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