Distribution of dust

In order to characterize the concentration of dust flowing inside a duct, a measured amount of dust must be extracted over a known period of time. This collection velocity must be the same as the internal duct flow velocity to avoid altering the distribution of dust particle sizes. In addition, a number of sample points over the entire duct cross sectional area is necessary to define the overall dust concentration. This method of sampling, known as gravimetric sampling under isokinetic conditions, was used to determine the dust concentrations at the various manufacturing areas in the Army Ammunition Plants. 

A global map of quartz abundance is given in Figure 14.12. In this case, the contribution of quartz is presented as the contribution to the bulk sediment from which biogenic carbonate and silica have been removed. This map is very similar to the global distribution of dust presented in Figure 11.4, reflecting the importance of aeolian transport for this detrital silicate. 

The prototype cotton-dust analyzer used in the initial study was designed to measure dust smaller than 100 pm, whereas a vertical elutriator in a card room measures only the dust that is smaller than about 15 pm. Differences in particle size distributions of dust from various types of cotton would likely affect the relationship between the two dust measurements. Therefore, we deemed it necessary to investigate the use of sizing screens with smaller openings i.e., openings whose size approximated the maximum size of particles collected by a vertical elutriator. The purpose of this report is to describe additional modifications to the cotton-dust analyzer and to present data on the performance of the machine when 17-, 50-, and 100-pm sizing screens were used. 

Figure 8. Cumulative distribution curves of distributions shown in Figure 7. Key , cotton control O, 0.60% Milube N-32 A, distribution of dust removed from card room atmosphere when Milube N-32 is added to cotton.

These factors include temp, humidity and motion, as well as distribution of dust, bacteria, odors and toxic gases. In air conditioning it is desirable that all factors be controlled but, if this is not feasible, at least the first three should be simultaneously controlled (see also Refrigeration and Ventillation)... 

Figure 7. Warm dust emission in early-type galaxies. Six galaxies are shown, each with separate images in stellar emission (3.6 /um) and warm dust emission (8.0 pm non-stellar ). The top three galaxies are classified as ellipticals and show no sign of warm dust emission at 8.0 pm. The bottom three galaxies are classified as lenticulars and show resolved warm dust. NGC 4203 appears face-on with several spiral arms emanating out from its nucleus, NGC 5363 appears somewhat inclined and shows two arms, and NGC 1023 shows a smooth distribution of dust.

Figure 9(a) shows schematically the distribution of dust around a young star, formed within a dense cloud, with material flowing onto the star through an accretion disk around the star, surrounded by a much larger dusty envelope. An outflow along the poles of the accretion disk, believed to be in the same... 

The parameters and C2 are valid for certain specific conditions (a particular dust, surface, and air duct), and as yet there is no basis for extending the meaning of these criteria to other cases of particle precipitation. Moreover, the distribution of dust particles in an air stream depends on the particle size, and in practice it is difficult to bring about a uniform concentration of dust in a stream. This circumstance limits the possibilities of practical calculation of t o on the basis of the parameters Ci and C2. Calculation of the capture coefficient as a function of the flow, surface, and dust properties and of the number of particles in the stream, however, is an approach that deserves attention and further development [256]. 

The critical role of LBP in the distributions of dust Pb loadings on interior surfaces recorded in Tables 6.29 and 6.30 can be seen in the data depicted in Table 6.31. When LBP is present and in good condition as defined in the national survey, 33% of units had a dust Pb hazard as defined by the U.S. HUD (1999), but in cases of significant deterioration of the LBP present, the corresponding percentage was roughly double, 61%. The absence of LBP in the unit resulted in only 6% having a dust lead hazard of some type on some surface. 

Fig. VI.24. Size distribution of spherical glass particles adhering to an oily (oil density 0.5 mg/cm ) surface as a function of the inclination of the plate to the flow axis, a) Flow velocity 5 m/sec b) flow velocity 25 m/sec. 1) 0 2) 45 3) 90 4) distribution of dust in the flow.

Dust often shrouds young stellar objects. This dust may collimate energetic outflows, and may ultimately form planetary systems. The study of drcumstellar dust may naturally be addressed by imaging in the thermal infrared however, extremely high spatial resolution will be needed to image the dust directly. Our initial efforts to carry out hi resolution measurements of LkHa 101 has produced some interesting constraints on the size and distribution of dust (Danen, Gwinn, and Bloemhof 1994). 

Deblay F, Sanchez J, Plattsmills T, Chapman M, Pauli G. The metrology of airborne particles carrying the principal aeroallergens. Rev Mai Respir 1995 12 343-352. Tovey ER, Chapman MD, Wells CW, Platts MT. The distribution of dust mite allergen in the houses of patients with asthma. Am Rev Respir Dis 1981 124 630-635. 

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