Efficient aerodynamics

The lungs have an efficient aerodynamic filter, which must be overcome for effective drug deposition to occur. 

For most conditions, the best effect is obtained when there exists a thick film of fluid between the moving surfaces affording efficient aerodynamic, hydrodynamic, or elastohydrodynamic lubrication. If the lubricating film is thinned or broken by operating conditions or system failure, additional protection is afforded by adsorbed films through boundary lubrication. Finally, under extreme conditions, protection against seizure and complete failure may be obtained as a result of chemical processes that produce weak oxide, sulfide, or phosphate, surface layers that can be more easily sheared that direct metal-metal contacts. For hydrodynamic and elastohydrodynamic lubrication, careful... 

Improved materials, coatings, and cooling techniques permit newer machines to operate at higher turbine inlet temperatures, yielding both increased output and efficiency. Further efficiency gains result from improved aerodynamics in the hot gas path, compressor, and turbine sections. Use is also made of variable inlet guide vanes (IGV). 

The grade efficiency T of most collectors can be expressed as a function of the aerodynamic particle size in the form of an exponential equation. It is simpler to write the equation in terms of the particle penetration Pf (those particles not collected), where the fractional penetration = 1 — T, when T is the fractional efficiency. The typical collection equation is... 

P = power generated by the turbine (windmill) in watts Cp = coefficient of performance which depends upon the aerodynamic efficiency of the rotor and varies with the number of blades and their profile. This factor is provided by the mill supplier and generally varies between 0.35 and 0.45 A = swept area of the rotor in... 

Centrifugal compressors can have problems at the inducer and blade tips. These parts of the blade can be excited by aerodynamic forces. Blade discs can have stresses at the rotor tips, which lead to cracks. To solve this problem, the offending part is removed and a scalloped disc results as seen in Figure 21-20. This type of disc experiences some efficiency loss (about 2 %). 

Of obvious importance to aircraft is the smoothness of exterior surfaces. Smooth aerodynamic surfaces reduce aerodynamic drag, resulting in higher airspeeds and increased efficiency. Mechanical fasteners, even countersunk flush fasteners, introduce disruptions in the airflow over the exterior surface. Even the slight deformation of thin sheets around fasteners produces drag. Adhesively bonded structure has no fasteners to disrupt airflow and is more capable of producing the smooth continuous contours that are so common on aircraft. 

PM Impingement-plate tower collection efficiencies range from 50 to 99 percent, depending upon the application. This type of scrubber relies almost exclusively on inertial impaction for PM collection. Therefore, collection efficiency decreases as particle size decreases. Short residence times will also lower scrubber efficiency for small particles. Collection efficiencies for small particles (< 1 fim in aerodynamic diameter) are low for these scrubbers hence, they are not recommended for fine PM control. 

Test bench methods for machines not too large for test cabins have been developed in order to obtain comparative results. In the case of particles, the tracer gas describes well the behavior of aerodynamic diameter particles less than 5 to 10 gm. For larger particles, correction factors should be used to modify the efficiency results obtained using the tracer gas technique. 

Aerodynamics is one of the applied sciences that plays a role in the overall consideration of energy. We have explained some of the more important physical aspects of aerodynamics, and illustrated how aerodynamics has an impact on energy efficiency. 

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