Aerodynamic measurements

A number of techniques have been used successfully to measure temperature profiles in flames thermocouples, resistance thermometers, shadowgraphs, interferometers, pyrometers, spectrometers, pneumatic probes, and aerodynamic measurements. The most useful of these techniques have proven to be the thermocouple method and the inclined slit technique. 

Active aerodynamic measures are being used successfully in aeronautical engineering to suppress wing flutter. Using additional control surfaces, con-... 

Aerodynamic measures for optimizing air resistance and their reviewed potentials are described in the literature [21, p. 33], [28, p. 23], [44, p. 675]. A substitution of the main and wide-angle mirror with a camera-monitor system (CMS) is an outstanding measure. The cross-sectional area of the vehicle is reduced and the drag coefficient can be optimized. In addition, wind noise and pollution of the side windows can be significantly reduced by the elimination of the outside mirrors [27, p. 40], [33, p. 536], [44, p.720]. For concept related direct flow of the mirror areas, the proven fuel saving potential of a CMS is estimated at 2.9 % [21, p. 59]. 

For determination of the aerodynamic diameters of particles, the most commonly apphcable methods for particle-size analysis are those based on inertia aerosol centrifuges, cyclones, and inertial impactors (Lundgren et al.. Aerosol Measurement, University of Florida, Gainesville, 1979 and Liu, Fine Paiiicles—Aerosol Generation, Measurement, Sampling, and Analysis, Academic, New York, 1976). Impactors are the most commonly used. Nevertheless, impactor measurements are subject to numerous errors [Rao and Whitby, Am. Ind. Hyg. A.s.soc.]., 38, 174 (1977) Marple and WiUeke, "Inertial Impactors, in Lundgren et al.. Aerosol Measurement and Fuchs, "Aerosol Impactors, in Shaw, Fundamentals of Aerosol Sci-... 

Because a filter sample includes particles both larger and smaller than those retained in the human respiratory system (see Chapter 7, Section III), other types of samplers are used which allow measurement of the size ranges of particles retained in the respiratory system. Some of these are called dichotomous samplers because they allow separate measurement of the respirable and nonrespirable fractions of the total. Size-selective samplers rely on impactors, miniature cyclones, and other means. The United States has selected the size fraction below an aerodynamic diameter of 10 /xm (PMiq) for compliance with the air quality standard for airborne particulate matter. 

The three major characteristics of particulate pollutants in the ambient atmosphere are total mass concentration, size distribution, and chemical composition. In the United States, the PM q concentration, particulate matter with an aerodynamic diameter <10 /nm, is the quantity measured for an air quality standard to protect human health from effects caused by inhalation of suspended particulate matter. As shown in Chapter 7, the size distribution of particulate pollutants is very important in understanding... 

Airborne particulate matter, which includes dust, dirt, soot, smoke, and liquid droplets emitted into the air, is small enough to be suspended in the atmosphere. Airborne particulate matter may be a complex mixture of organic and inorganic substances. They can be characterized by their physical attributes, which influence their transport and deposition, and their chemical composition, which influences their effect on health. The physical attributes of airborne particulates include mass concentration and size distribution. Ambient levels of mass concentration are measured in micrograms per cubic meter (mg/m ) size attributes are usually measured in aerodynamic diameter. Particulate matter (PM) exceeding 2.5 microns (/i) in aerodynamic diameter is generally defined as coarse particles, while particles smaller than 2.5 mm (PMj,) are called fine particles. 

Black smoke (BS) is a particulate measure that typically contains at least 50% respirable particulates smaller than 4.5 mm in aerodynamic diameter, sampled by the British smokeshade (BS) method. The reflectance of light is measured by the darkness of the stain caused by particulates on a white filter paper. The result of BS sampling depends on the density of the stain and the optical properties of the particulates. Because the method is based on reflectance from elemental carbon, its use is recommended in areas where coal smoke from domestic fires is the dominant component of ambient particulates. 

FIGURE 5.28 Estimated overall airway deposition as a function of initial particle size and particle hygroscopicity for particles with mass median aerodynamic diameters (MMAD) between 0.1 and 10 p.m. ° Geometric dispersion, a measure of particle size distribution, principally affects only smaller MMAD,... 

Aerosol dynamics are based on spherical particles, a premise which almost never exists in practice. However, if there is consistency in handling the aerosol dynamics calculations, the aerodynamic diameter (see Section 13.5.2.2) that is measured gives fairly accurate predictions of aerodynamic behavior. As a result, the difference between the real shape and size of the particles and the aerodynamic shape and size is unimportant for most practical purposes. 

The electrical low-pressure impactor was used to measure the number concentrations of diesel exhaust particles. The particle size distribution ranges from 30 nm upward were then determined using the aerodynamic diameter as the characteristic dimension. ... 

Aerodynamic drag has also been used to capture energy from the wind. Drag mechanisms consist of flat or cup-shaped devices that turn the rotor. The wind simply pushes the device around the main shaft. Anemometers used to measure wind speed are often drag devices, as are traditional farm windmills. 

Coefficient entry or discharge) The ratio of aerodynamic (effective) area to the measured area of an opening. The value for a square-edged hole of 0.61 is used for most building openings. 

Aerodynamic area The effective theoretical open area of an opening. It is related to the measured area by the coefficient of entry or discharge (Cd). 

In addition, this type of compressor tends to have both the suction and discharge ports on the same side of the compressor s housing. As a result, there is a potential for aerodynamic instability within the compressor. Orientation of the primary (X-axis) radial measurement point should be opposite the discharge port and oriented toward the discharge. The secondary (Y-axis) radial point should be in the direction of shaft rotation and 90° from the primary radial point. 

In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow —the natural science of fluids (liquids and gases) in motion. It has several subdisciplines itself, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics offers a systematic structure that underlies these practical disciplines, that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves calculating various properties of the fluid, such as velocity, pressure, density, viscosity and temperature, as functions of space and time. 

Based on 46 measurements, the activity median aerodynamic diameter of Pb-212 averaged 0.13 pm (0g = 2.97), while Pb-214 averaged 0.16 pm (Og = 2.86). The larger median size of Pb-214 was attributed to a-recoil depletion of smaller aerosols following decay of aerosol-associated Po-218. 

Aerodynamic Size Distributions of Naturally-Radioactive Aerosols. Measurements of radionuclide distributions using cascade impactors indicate that Be-7 and Pb-210 are associated with larger aerosols than Pb-212 and Pb-214 (Robig et al., 1980 Papastefanou and Bondietti, 1986). Measurements of Pb-210 associations over oceans indicated activity median aerodynamic diameters (AMAD) near 0.6 pm (Sanak et al., 1981). The impactor measurements of Moore et al. (1980) on Pb-210, Bi-210, and Sr-90 sizes in continental air indicated that about 80% of the activity from all three nuclides was associated with aerosols below 0.3 pm. That work also determined that the mean age of aerosol Pb-210 was about a week. Knuth et al. (1983) compared Pb-210 and stable Pb sizes at a continental location and found that 78% of the Pb-210 found below 1.73 pm was smaller than 0.58 pm. Young (1974) reported that the most of the Be-7 in the atmosphere was associated with submicron aerosols. 

Measurements on aerodynamic sizes of atmospheric aerosols and associated radionuclides were carried out with Anderson 2000, Inc., 1-ACFM Ambient Impactors with or without the Anderson low-pressure modification, as well as with Sierra model 236 (six-stage) high-volume impactors (HVI). The 1-ACFM design operated at 28... 

Table I presents the average aerodynamic distributions of Pb-212 and Pb-214, as well as the frequency with which Pb-214 or Pb-212 was the dominant isotope in each size range. The Aitken nuclei fraction (below 0.08 pm) contained a higher percentage of Pb-212 activity compared with Pb-214 in 69.6% of the measurements. The predominance of Pb-212 in this fraction is also illustrated by the distributions reported in Figure 1. In the remaining measurements, where Pb-214 was fractionally more abundant below 0.08 um, the disparity between the relative amounts of each isotope was not nearly as dramatic. Conversely, Figure 1 and Table I illustrate that Pb-214 is generally enriched in the accumulation mode aerosol, particularly between 0.11 and 0.52 ]xm, where most of the surface area and mass occurs.

Figure 1. Representative plots from 46 low-pressure impactor measurements, illustrating aerodynamic size (Dp) distributions of Pb-212 and Pb-214 (R = radioactivity), (a) type results occurred 46% of the time, (b) 39% of the time, (c) 8.7% of the time, and (d) 6.5% of the time. Lower Dp limits are arbitrary.

Pb-212 vs S0%- LPI Distributions. Figure 3 presents a summary of the average Pb-212 AMADs and SOj MADs (mass median aerodynamic diameters) determined from a series of LPI measurements made during the period January to October, 1985. The Pb-212 data were derived from collections made at the same time as S0jj and from measurements made to compare Pb-212 vs Pb-214. The mean aerodynamic diameter of Pb-212 was about three times smaller than SoJ . Much less sulfate was found in the aerosol fraction below 0.08 um, compared with Pb-212. While Pb-212 was largely absent above 0.52 um, about 20% of the SoJ occurred above this size. 

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