Dust particles definition

Smoke is taken as having a particle size of less than one pm. Dust consists of particles I-76 pm in diameter. Grit can be interpreted as particles larger than dust. These definitions were taken from the Beaver Report of November 1954 which formed the basis for the 1956 Act. 

Riesenfeld and Bohnholtzer and Riesenfeld and Schumacher used ozone concentrated by liquefaction and distillation. From their kinetic measurements they conclude that a reaction of the second order and one of the first order take place simultaneously at quite low pressures, 6-60 mm. Hg the first order reaction predominates. The velocity constants of the second order reaction are not influenced by the total pressure, while those of the first order reaction appear to be inversely proportional to the total pressure. The figures given show that the first order reaction at the lower pressures is considerably influenced by the surface, and is quite probably a heterogeneous reaction, though the authors themselves do not consider this to be definitely shown. The decomposition appears to be rather sensitive to catalysts such as dust particles. 

The flame is not, however, a discontinuity. There are definite gradients of temperature and composition because of conduction of heat and diffusion of reaction products into the fresh gas. The temperature gradients have been studied by three techniques direct measurement with very fine thermocouples (24, 25, 43) refraction of a narrow slit of light (11, 16) and tracing the path of a stroboscopically lighted dust particle and computing temperature from its direction and velocity (l, 27). 

Soluble substances, when brought into solution, may show slight physical impurities, such as fragments of filter paper, fibers, and dust particles. Unless excluded by definite tests or other requirements however, significant amounts of black specks, metallic chips, glass fragments, or other insoluble matter are not permitted. 

The field of protoplanetary dust size distributions and properties can be confusing. We therefore begin by briefly reviewing the most common definitions and assumptions. Owing to the nature of astrophysical observations, extrasolar dust particles are usually described in terms of their optical properties. This is generally not the case for Solar System material, which is available to direct laboratory studies. This gives rise to potentially confusing differences in nomenclature. 

Solid bodies of extraterrestrial material that penetrate the atmosphere and reach the Earth s surface are called meteorites. Other extraterrestrial materials include micrometer-sized interplanetary dust particles (IDEs) collected in the lower stratosphere and polar ices. Most meteorites and IDEs are fragments of asteroids, but some IDEs may represent cometary material and some meteorites are fragments of the planets Mars and Earth s moon. Meteorites recovered following observed falls are called/a// those which cannot definitely be associated with observed falls are called finds. Meteorites are given names based on the location where they were recovered (e.g., the Allende meteorite fell in Allende, Mexico). Meteorites recovered in Antarctica and the deserts of Australia and northern Africa are given names and numbers, because numerous samples are found in the same locations. Fragments thought to be of the same meteorite fall, which, in Antarctica or hot deserts, may have different numbers or even names because they were found in different locations, are called... 

The graphitic particles consist almost entirely of carbon atoms, probably bonded to each other in a variety of complex forms. PAH clusters have been hypothesized for some time and evidence is accumulating that they occur abundantly in the ISM. No specific PAH molecule, however, has as yet been definitively identified in the interstellar medium. Whatever form they may take, dust particles are now thought to be remnants of stellar explosions, in which a star expels part or all of its mass into the ISM. 

When transformation of a less stable into a more stable phase occurs, the change does not take place at one moment throughout the whole phase, but proceeds from definite points or growth centres (nuclei). Such nuclei may form spontaneously in a supercooled phase, as is seen, for example, in the cloud formation produced on the cooling of a vapour by adiabatic expansion. The influence of dust particles and of gaseous ions in increasing the number of condensation nuclei, is well known. 

The term particle (or grain) size refers to the structural make-up of such substances as granulates, powders, dusts, granular mixes, and suspensions. Knowledge of the particle size, in conjunction with the comminution process, determines such details as grinding efficiency and ultimate product fineness. To establish particle sizes and their distribution within powdered systems, the user can have recourse to a number of different measuring processes designed to indicate, with appropriate particle definition, details of the probable equivalent diameter of a particle. 

For dust particles and baseballs, where m is relatively large, the term on the right becomes nearly zero, and the uncertainties of position and velocity are quite small. The path of a baseball has meaning. For electrons, however, the uncertainties in position and momentum are normally quite large. We cannot describe the electron in an atom as moving in a definite orbit. 

The detailed results of the photochemical models are dependent on the adopted UV radiation field as well as on the photodissociation and photoionisation cross-sections, which in principle can be obtained by laboratory or theoretical studies, and on the nature of the dust particles for which the chemical composition, size and hence optical properties are poorly known. In the absence of definitive information, detailed models of the photochemistry have relied on some rather simplistic approaches to the radiative transfer of UV photons through the envelope. Nejad and Millar (1987,1988) have used the approach developed by Jura and Morris (1981) which assumes that the dust grains absorb but do not scatter and leads to a numerically simple equation for the intensity of UV radiation at any point in the envelope. On the other hand, Glassgold and co-workers have used a formalism devised by Gerola and Glassgold (1978) in which the scale-length, dp for photodissociation of any species is used to diminish the intensity incident on the CSE, that is, the intensity is reduced by a quantity exp(-d(/r). These authors have also included the effects of both continuum and line self-shielding in their calculations. 

Here, if the fiber of radius rf is perpendicular to the gas flow, then 2b is the width of the region of gas flow (see Figure 6.3.9A) which is cleaned completely of any particles by the single fiber. An essentially identical definition may be employed when the filter bed consists of granular particles of radius rf-, in that case, 2b will be the diameter of a cylindrical tube of contaminated gas, which will be cleaned of dust particles by the spherical collector in the filter bed. The value of b is obtained from the solution to the governing equation (6.3.40) and the gas velocity profile. The streamline corresponding to b is the limiting trajectory. 

Figure 17-46 shows such a performance curve for the collection of coal fly ash by a pilot-plant venturi scrubber (Raben "Use of Scrubbers for Control of Emissions from Power Boilers, United States-U.S.S.R. Symposium on Control of Fine-Particulate Emissions from Industrial Sources, San Francisco, 1974). The scatter in the data reflects not merely experimental errors but actual variations in the particle-size characteristics of the dust. Because the characteristics of an industrial dust vary with time, the scrubber performance curve necessarily must represent an average material, and the scatter in the data is frequently greater than is shown in Fig. 17-46. For best definition, the curve should cover as wide a range of contacting power as possible. Obtaining the data thus requires pilot-plant equipment with the flexibility to operate over a wide range of conditions. Because scrubber performance is not greatly affected by the size of the unit, it is feasible to conduct the tests with a unit handling no more than 170 m3/h (100 ftVmin) of gas.

Measurement and analysis of trash and dust in cotton is important in the prediction of dust generation potential, in relation to byssinosis (14) and rotor spinning performance (15). By definition, trash is the nonlint particles including dust which settle under the influence of gravity in the processing of cotton. Dust is the finer material capable of being dispersed in air. Particulate burden is the combined trash and dust level in cotton. 

Figures listed are for best conditions (dry. sized and without dust)—The minimum angle will increase os site of particles decrease and with higher moisture content. For other conditions refer to S-A Engineers for definite recommendations.

Detergency is about the theory and practice of the removal of foreign material from solids by surface-active substances. This definition excludes pure mechanical cleaning. Also a pure chemical cleaning, e.g., by solvation of the foreign material, is not considered. In textiles oily substances usually attach to the fibres (animal fats, fatty acids, hydrocarbons, etc.). Also dust, soot, and other solid particles have to be removed in a washing process. In order to test the effectiveness of a surfactant, textiles are often polluted with standard dirt mixtures and cleaned with a standard washing procedure (launderometer). Often cleanliness is measured on the basis of optical reflectivity of white textiles. 

As can be seen from the above table, the ACGIH definition of respirable dust is almost identical with that of the AEC, differing only for a 2-(im-aerodynamic-diameter particle. Lippmann (1989) points out that this difference appears to be a recognition by the ACGIH of the characteristics of real particle separators. 

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