Resistance aerodynamic

The vertical turbulent flux of a quantity, say, C, through the (constant-flux) surface layer is expressed as 

If (19.8) is integrated across the depth of the constant-flux (i.e., surface) layer from 3 down to Z2, the flux Fa may be written as 

The integral in (19.12) is evaluated from the bottom of the constant-flux layer (at co, the roughness length) to the top (Zr, the reference height implicit in the definition of Vtj). 

Example 19.1 Explicit Expressions for ra If the stability-dependent temperature profile function is given by (16.75), 

The theory is applicable only in the surface layer where the flux is nondivergent, that is, —3 / / 2. An approximate maximum vertical extent is -- 100 m. 

---

The Aerodynamic Resistance of Cooling Towers Konikowski, T. Zembaty, W. 

Evaluation of aerodynamic resistance of projectiles) ll)M.Rauscher, "Introduction to Aeronautical Dynamics," Wiley, NY(1953) 12)F.I.Frankl E.Karpo-vich,"Gas Dynamics of Thin Bodies," translated from the Rus, Interscience, NY(1953) 13)T. von Karman, "Aerodynamics, ComellUnivPress, Ithaca, NY(1954) 14)... 

Although multiple scavenging improves separation, coarse particles crossing the air stream on each cascade step collide and mix with fines. This precludes sharp separation and decreases the efficiency. Another disadvantage of the device is its high aerodynamic resistance (pressure drop of about 2.5-3.5kPa), resulting from the vortexes formed in cascades turn points. 

The experimental points for the sticky artificial grass in Fig. 6.10 lie close to the theoretical curves, showing that the Lycopodium particles were deposited at the maximum rate allowed by the aerodynamic resistance. Deposition to real grass was limited by bounce-off. For both... 

In the last two columns of Table 6.4 the turbulent deposition velocities of mass and momentum are shown. For droplets, vt and vm are approximately equal, indicating that capture by the surface is efficient, and aerodynamic resistance the limiting factor. 

To ensure uniform resistance to vapor and liquid flow throughout the bed Concentrated pockets of aerodynamic resistance can lower the effective tower cross-section area, thus reducing capacity. 

The energy used per mile driven19 depends on the weight, aerodynamic resistance, and other physical characteristics of vehicles. Therefore, any measure of the energy used per... 

Evaluation of aerodynamic resistance of projectiles) 11)M.Rauscher, "Introduction to Aeronautical Dynamics," Wiley, NY( 1953) 12)F.I.Frankl E.Kaipo-... 

The flux of trace gases and particles from the atmosphere to the surface is calculated by multiplying concentrations in the lowest model layer by the spatially and temporally varying deposition velocity, which is proportional to the sum of three characteristic resistances (aerodynamic resistance, sublayer resistance, and surface resistance). The surface resistance parametrization developed by Wesely (1989) is used. In this parametrization, the surface resistance is derived from the resistances of the surfaces of the soil and the plants. The properties of the plants are determined using land-use data and the season. The surface resistance also depends on the diffusion coefficient, the reactivity, and water solubility of the reactive trace gas. 

Using active carbons and some other carbonic adsorbents, several processes have been elaborated to output commercial products (sulphuric acid, sulphur, and sulphur dioxide), Reinluft (FRG), Hitashi (Japan), and Westvaco (USA). However, because of the deficit and high cost of adsorbents, these processes may be recommended only for purification of small volumes of ejected gases. Recently, the methods using natural acid-stable clinoptilolite- and mordenite-type zeolites as adsorbents have been introduced into industry. It is safe to say, however that general drawback of all granular physical adsorbents is their low sorption activity at a sufficiently low concentration of SO2 n g comparatively high aerodynamic resistance. 

The main features of purification filters based on ion exdiange fibrous materials are high sorption capacity and purification degree, low aerodynamic resistance, and efficient regeneration. As studies have shown [4 ], at a gas,flow rate of 0.1 m/s in a dense layer of a non-woven material, the length of a working layer is 2 mm which makes it possible to use filtering cloths of 10—20 mm thickness. The area of the filter is 20 m per 1 m of operation volume which corresponds to specific output, 7 10 m /h of purified air. The aerodynamic resistance of filters in this case does not exceed 20 Pa. 

Pyrolytic BN was deposited on Nicalon NL202 silicon carbide yarns at 1000-1200°C to improve aerodynamic resistance and oxidation behavior of silicon carbide. Yarns were fed into a CVD furnace at a rate of 0.01 m/s. The pBN was made by... 

In the event the surface does offer chemical resistance by virtue of slower reaction rates, resistance to acid attack, etc., the gas concentration will not be zero at the surface and the dry deposition rate will be reduced accordingly. Thus structures made or coated with such materials will show a different relationship between calculated deposition velocities, as presented here, and the actual operational values, which may be governed more by the material properties and less by aerodynamic resistance. This would be an important property to establish, by testing over a range of aerodynamic conditions. 

The dispersion matrix D,j is a discrete form of the transition probability P in Eq. (16) and thus carries all the required information about the velocity field. Its elements have the dimension of aerodynamic resistance (s m ). The elements of column j of D-,j are found by considering (/>jAzj to be a steady unit source, with sources in all other canopy layers set to zero. A theory of turbulent dispersion is used to calculate the concentration field c(z) resulting from this source distribution. The elements of column j of D-,j are then given by... 

It has proved useful to interpret the deposition process in terras of an electrical resistance analogy, in which the transport of material to the surface is assumed to be governed by three resistances in series the aerodynamic resistance ra, the quasi-laminar layer resistance rt, and the surface or canopy (the term canopy refers to the vegetation canopy) resistance rc. The total resistance, rt, to deposition of a gaseous species is the sum of the three individual resistances and is, by definition, the inverse of the deposition velocity ... 

To ensure a constant-flux layer, one can simply move the measurement height closer to the surface. For the eddy correlation method, however, the response time of the instrument must be faster as the measurement height approaches the surface, because high-frequency turbulent eddies then contribute proportionally more to the concentration fluxes than at higher levels. On the other hand, fluxes measured very close to the surface may be less representative of those over the entire area for which the measurement is intended. For the gradient method, the requirement that z/zo 3> 1 (based on the requirements of similarity theory) constrains the minimum measurement height. Under very stable conditions, when turbulence may be intermittent, turbulent fluxes may become very small, and the constant-flux layer may be very shallow. Under conditions such as these, it can be quite difficult to determine the aerodynamic resistance term ra. 

X for particles subject to aerodynamic resistance in the Stokes drag regime is given by... 

---