Particles in air

TABLE 14.1 The Free-Falling Velocity of a Spherical Particle in Air (20 °C, 1.023 bar) based on Stokes s Theory... 

Brownian diffusion (Brownian motion) The diffusion of particles due to the erratic random movement of microscopic particles in a disperse phase, such as smoke particles in air. 

Figure 4-9 is convenient for quick checks of terminal settling velocities of solid particles in air and in water [23]. 

For most purposes, the correlations for jD presented in Tables 12.1 and 12.2 also suffice for estimating jH. There is, however, one additional correlation for fluidized beds that is worth noting. On the basis of data for the fluidization of 20 to 40 mesh silica and alumina gel particles in air at Reynolds number values (DpG/fi) ranging from 9 to 55, Kettenring et al. (92) suggest that... 

Levitation is a stable condition in which a particle responds to the oscillating fluid in such a way that the influence of finite buoyancy, or gravity, forces is completely neutralized so that the particle oscillates about a fixed position (Houghton, 1963, 1964, 1966, 1968 Krantz, Carley and Al-taweel, 1973 Tunstall and Houghton, 1968 Van Oeveren and Houghton, 1971). Figure 37 (Liu, 1983) shows the levitation of solid particles in air under oscillation caused by a sonic generator located at the bottom of the column. 

Fig. 30. Snapshot of particle volume fraction fields obtained while solving a kinetic theory-based TFM. Fluid catalytic particles in air. Simulations were done over a 16 x 16 cm periodic domain. 128 x 128 cells (shown in the figure). The average particle volume fraction in the domain is 0.05. Dark (light) color indicates regions of high (low) particle volume fractions. Squares of different sizes illustrate regions (i.e., filters) of different sizes over which averaging over the cells is performed. Source Andrews and Sundaresan (2005).

Zirconium particles in air are sensitive to ignition by static electricity. This sensitivity increases with decreasing particle size. When Zr particles are heated in air, reaction with oxygen occurs at their surface. This reaction proceeds very violently to produce high-temperature zirconium oxide. A large number of bright light streams are emitted from the particles when they come asunder. The reaction process is represented by... 

Zr particles react violently with BaCr04 particles, similarly to the burning of Zr particles in air. However, a mixture of Zr particles and BaCr04 particles is relatively insensitive to friction or mechanical shock. DTA and TG data indicate that an exothermic reaction accompanied by a small mass loss occurs at 542 K. The maximum exothermic peak is at 623 K and the rate of the exothermic reaction-gradually decreases as the temperature is increased further. The observed characteristics are highly dependent on the size of the Zr particles because the reaction occurs at their surface. The exothermic peak observed at 623 K becomes higher... 

The primary consideration in the burning of a metal particle in air is the limitation of the temperature attained by the boiling of the resultant oxide. 

Environmental Fate. It can be concluded from the transport characteristics that surface water sediment will be the repository for atmospheric and aquatic thorium. Normally, thorium compounds will not transport long distances in soil. They will persist in sediment and soil. There is a lack of data on the fate and transport of thorium and its compounds in air. Data regarding measured particulate size and deposition velocity (that determines gravitational settling rates), and knowledge of the chemical forms and the lifetime of the particles in air would be useful. 

Figure 10-15 Concentration and temperature pro-files fflDund a burning carbon particle in air Pq = 0.2 atm and Tq = 25°C). The concentration of O2 falls to zero at the surface aid the temperature rises to nearly the adiabatic flame temperature.

Finally, a product of a pyrotechnic reaction may vaporize from the reaction zone and subsequently condense as fine particles in air, creating a smoke. Potassium chloride (boiling point 1407°C) produces smoke in many potassium chlorate and potassium perchlorate compositions, although smoke is usually not a goal sought from these mixtures. 

Two basic processes are used to create smoke clouds the condensation of vaporized material and the dispersion of solid or liquid particles. Materials can either be released slowly via a pyrotechnic reaction or they can instantaneously be scattered using an explosive material. Technically, a dispersion of fine solid particles in air is termed a smoke, while liquid particles in air create a fog. A smoke is created by particles in the 10 -10 " meter range, while larger suspended particles create a dust (1). ... 

Atmospheric chemists and other scientists who have focused on pollution and global climate change have much to contribute to national security and homeland defense. These scientists have developed computational methods to accurately model and in many cases predict the transport of pollutants and particles in air or water. These same tools can be used to predict the effect of release of a chemical agent in an urban area so that appropriate emergency response plans can be developed. 

Fig. 10.15 Drag coefficient for rigid spherical particles in air as a function of Mach number with Reynolds number as parameter, for the case where the absolute temperatures of the particle and fluid are essentially the same.

Schroeder, W. H., and P. Urone, Formation of Nitrosyl Chloride from Salt Particles in Air, Enriron. Sci. Technol., 8, 756-758 (1974). 

In short, some particles in air can become quite acidic. For example, the pH of particles in southern California was estimated to be 0.2 and below (Li et al., 1997). 

In short, data such as those in Figs. 9.64 and 9.65 support the use of the octanol-air partitioning coefficient as a useful parameter for characterizing gas-particle partitioning of SOC into liquid particles or liquid layers on particles in air. 

As a result, while such methods have been very useful in the past and continue to be applied for initial surveys of air quality in areas in which measurements have not been made in the past, they have generally been abandoned in favor of instrumental methods of analysis. As a result, this chapter focuses on the most commonly used instrumental, often spectroscopic, methods for measuring air pollutants, trace gases, and particles in air (e.g., see Roscoe and Clemitshaw, 1997). The focus is on tropospheric measurements, although, in most cases, the same techniques are used in the stratosphere. 

The total mass of particles per unit volume of air is one of the major parameters used to characterize particles in air and, along with size, is the basis of air quality standards for particulate matter (see Chapter 2). Methods of mass measurement include gravimetric methods, /3-ray attenuation, piezoelectric devices, and the oscillating microbalance. 

Stoffels, J. J., and C. R. Lagergren, On the Real-Time Measurement of Particles in Air by Direct-Inlet Surface-Ionization Mass Spectrometry, Inf. J. Mass Spectrom. Ion Phys., 40, 243-254 (1981). 

---