Aerodynamic influence

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. 

The science of building aerodynamics considers the influence of wind forces over buildings and the associated mechanics of fluids these are complex in nature and are not considered here. It is sufficient to briefly consider Fig. 9.21, which shows how wind passing over a building produces a positive pressure on one side and a negative pressure on the other side. It is this pressure difference that produces airflow through openings. The combined wind and stack effects vary with the seasons. 

One significant result from the studies of stretched premixed flames is that the flame temperature and the consequent burning intensity are critically affected by the combined effects of nonequidiffusion and aerodynamic stretch of the mixture (e.g.. Refs. [1-7]). These influences can be collectively quantified by a lumped parameter S (Le i-l)x, where Le is the mixture Lewis number and K the stretch rate experienced by the flame. Specifically, the flame temperature is increased if S > 0, and decreased otherwise. Since Le can be greater or smaller than unity, while K can be positive or negative, the flame response can reverse its trend when either Le or v crosses its respective critical value. For instance, in the case of the positively stretched, counterflow flame, with k>0, the burning intensity is increased over the corresponding unstretched, planar, one-dimensional flame for Le < 1 mixtures, but is decreased for Le > 1 mixtures. 

The mechanism is essentially a combination of the deformation of a round liquid jet by aerodynamic forces and the instability of the deformed jet. The liquid jet is first accelerated rapidly in the high speed air stream (Fig. 3.3b). The jet diameter is thus significantly reduced as it interacts with the surrounding air stream. The direction of the thinning capillary liquid jet is influenced by the interaction between the liquid jet and the turbulent structures of the surrounding air stream. The formation of... 

In addition to these physical properties and process variables, the flow, flow direction, and shock wave of ambient air/gas relative to liquid jet may significantly influence the resultant droplet size distribution. In high-speed aerodynamic atomization, different flow arrangements have been used, 244 including (a) injection of liquid... 

Some quantitative studies1498115011 on droplet size distribution in water atomization of melts showed that the mean droplet size increases with metal flow rate and reduces with water flow rate, water velocity, or water pressure. From detailed experimental studies on the water atomization of steel, Grandzol and Tallmadge15011 observed that water velocity is a fundamental variable influencing the mean droplet size, and further, it is the velocity component normal to the molten metal stream Uw sin , rather than parallel to the metal stream, that governs the mean droplet size. This may be attributed to the hypothesis that water atomization is an impact and shattering process, while gas atomization is predominantly an aerodynamic shear process. 

In the late 1920s and early 1930s many popular cars combined smooth curved surfaces from aerodynamic studies with the integration of components into the main body of the car. The visual influences ranged from aircraft and boats to racing cars. 

The influence of conditions on the droplet size where the spray sheet disintegrates through aerodynamic wave motion may be represented by the following expression proposed by Dombrowski and Monday134 for ambient densities around normal atmospheric conditions ... 

Studies have shown that in order to clear the oropharyngeal impaction barrier (comprising the mouth, throat, and pharynx), particles with aerodynamic diameters smaller than 5 pm are required [3,4]. Only particles with aerodynamic diameters less than 3 pm reach the terminal bronchi and the alveoli in significant numbers [5]. Therefore, the particle diameter required to be produced by the delivery system depends to a great extent on the intended target lung tissue. Lung deposition is also affected substantially by the specific inhalation dynamics of the patient, which in turn are influenced by the delivery device. This article addresses various attributes of the dry powder inhalation product, from intrinsic material properties to final product performance. 

Rapid aerodynamic flow past obstacles involves adiabatic compressions and rarefactions, and is influenced by relaxation of internal degrees of freedom in a way similar to shock phenomena. This effect has been quantitatively treated by Kan-trowitz18, who developed a method for obtaining relaxation times by measuring the pressure developed in a small Pitot tube which forms an obstacle in a rapid gas stream. This impact tube is not a very accurate technique, and requires a very large amount of gas it has been used to obtain a vibrational relaxation time for steam. 

The superposition of electrostatic forces on particle behavior near a filter mat can have appreciable influence on filtration efficiency. The deposition patterns can take on significant treeing or branching of agglomerates on individual fibers. This aerodynamically distorts the cylindrical collector surface and branches the surface area, as well as distorting the electrical field around the collector. 

The aerodynamic drag on a given droplet is not influenced by its neighboring droplets. 

Factors that influence the destruction efficiency include local temperatures and gas composition, residence time, extent of atomization of liquid wastes and dispersion of solid wastes, fluctuations in the waste stream composition and heating value, combustion aerodynamics, and turbulent... 

As mentioned above, Eq. 5.15 implies that the aerodynamic diameter of a rod or fiber will be influenced very little by its length, being much more dependent on its cross-sectional diameter. Hence fibers of different lengths but similar cross-sections will have similar aerodynamic properties, despite large differences in mass. 

Berry, J., Kline, L. C., Sherwood, J. K., et al. (2004), Influence of the size of micronized active pharmaceutical ingredient on the aerodynamic particle size and stability of a metered dose inhaler, Drug Dev. Ind. Pharm., 30,705-714. 

Elsaadawy, E.A. and Britcher, C.P. (2002). The extent of a laminar boundary layer under the influence of a propeller slipstream. AIAA Applied Aerodynamics Conf. paper no. AIAA 2002-2930. 

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