Air masses

It is used as a fluorinating reagent in semiconductor doping, to synthesi2e some hexafluoroarsenate compounds, and in the manufacture of graphite intercalated compounds (10) (see Semiconductors). AsF has been used to achieve >8% total area simulated air-mass 1 power conversion efficiencies in Si p-n junction solar cells (11) (see Solarenergy). It is commercially produced, but usage is estimated to be less than 100 kg/yr. 

Fig. 1. Absorption spectra of (-----) H2O2, and (—) O in aqueous media together with the (-----------) terrestrial air mass one (AMI) solar emission spectmm...

The use of wind as a renewable energy source involves the conversion of power contained in moving air masses to rotating shaft power. These air masses represent the complex circulation of winds near the surface of Earth caused by Earth s rotation and by convective heating from the sun. The actual conversion process utilizes basic aerodynamic forces, ie, lift or drag, to produce a net positive torque on a rotating shaft, resulting in the production of mechanical power, which can then be used directly or converted to electrical power. 

Elastic scattering is also the basis for Hdar, in which a laser pulse is propagated into a telescope s field of view, and the return signal is collected for detection and in some cases spectral analysis (14,196). The azimuth and elevation of the scatterers (from the orientation of the telescope), their column density (from the intensity), range (from the temporal delay), and velocity (from Doppler shifts) can be deterrnined. Such accurate, rapid three-dimensional spatial information about target species is useful in monitoring air mass movements and plume transport, and for tracking aerosols and pollutants (197). 

Example 13 Packed Column Pressure Drop Air and water are flowing coiinterciirrently through a bed of 2-inch metal Pali rings. The air mass velocity is 2.03 kg/s-m (1500 Ihs/hr-fd), and the liquid mass velocity is 12.20 kg/s-m (9000 Ihs/hr-fr). Calculate the pressure drop hy the generalized pres-... 

Density of ambient air, mass/voliime p.3 Initial density of released material, mass/voliime... 

Sinee the generator is eonneeted to the eleetrieal grid, PRT speed is fixed. For induetion-type motor/generators, some speed variation is possible due to motor/generator slip, but this is only a small pereentage of rated speed. In any event, the speed eannot be used to eontrol other proeess parameters (e.g., air mass flow to the regenerator). 

Atmospheric haze can occur over regions of several thousand square kUometers, caused by the oxidation of widespread SO2 and NO2 to sulfate and nitrate in relatively slow-moving air masses. In the eastern United States, large air masses associated with slow- moving or stagnating anticyclones have become sufficiently contaminated to be called hazy blobs. These blobs have been tracked by satellites as they develop and move across the country (15). 

Fig. 10-9. The evolution and transport of a large hazy air mass. Contour maps of noon visibility for June 25-July 5, 1975. Source Lyons, W. A., and Husar, R. B., Mon. Weather Rev. 104, 1623-1626 (1976).

A survey by national park personnel indicates that large areas of the United States are subject to varying degrees of visibility degradation (1). The middle portion of the eastern half of the country and the Florida Gulf Coast are subject to widespread hazy air masses associated with stagnation conditions. Large portions of the western half of the country are subject... 

Zannetti et al. (20) did an analysis of visual range in the eastern United States again showing the importance of humidity but also showing the importance of air mass type, which is usually related to its direction of origin. 

The gas turbine eontrol loop eontrols the Inlet Guide Vanes (IGV) and the Gas Turbine Inlet Temperature (TIT). The TIT is defined as the temperature at the inlet of the first stage turbine nozzle. Presently, in 99% of the units, the inlet temperature is eontrolled by an algorithm, whieh relates the turbine exhaust temperature, or the turbine temperature after the gasifier turbine, the eompressor pressure ratio, the eompressor exit temperature, and the air mass flow to the turbine inlet temperature. New teehnologies are being developed to measure the TIT direetly by the use of pyrometers and other speeialized probes, whieh eould last in these harsh environments. The TIT is eontrolled by the fuel flow and the IGV, whieh eontrols the total air mass... 

If the sphere of air mass moves upward in an adiabatic process but in an atmosphere with a subadiabatic lapse rate, the sphere follows a temperature change given by the adiabatic slope but when it arrives at point Zj, it is at a lower temperature than its surroundings, but at the same pressure. As a result, it is heavier than the surroundings and tends to fall back to its original position. This condition is called stable. In a stable atmosphere pollutants will only slowly disperse, and turbulence is suppressed. 

Airshed a geographic area that, because of topography, meteorology, and/or climate, is frequently affected by the same air mass. 

Back Trajectory a trace backwards in time showing where an air mass has been. 

Stable Air Mass an air mass which has little vertical mixing. See temperature inversion. 

Unstable Air Mass an air mass that is vertically well mixed. See also stable air mass, temperature inversion. 

Technical calculations dealing with humid air are reasonable to solve with dry air mass flow rates, because these remain constant in spite of changes in the amount of water vapor in the air. For that reason a definition for enthalpy,... 

We denoted the mass of dry air in a volume V as that is, p, - w,/Vj, and the mass of water vapor in V as m, that is, pp = mp/Yp. In practical calculations we usually handle volume flow volume flow is known in the suction inlet of a fan when the operating point of the fan is defined. Volume flow q, expressing the total air flow or the combined volume flow of water vapor and dry air, is not constant in various parts of the duct, because the pressure and temperature can vary. Therefore in technical calculations dealing with humid air, materia flows are treated as mass flows. Also, while the humidity can vary, the basic quantity is dry air mass flow w,(kg d.a./s). If, for instance, we know the volume flow q,. of a fan, the dry air mass flow through the fan is... 

Pressure and humidity have also an effect on the mass flows. We continue Examples 2a and 2b by calculating the dry air mass flow in a fan when the humid air volume flow in the fan is 0.8 m /s. According to Eq. (4.91) and the calculations above, we obtain... 

Thus the total mass flows tn= m, + m,) differ in different cases. Water vapor flow th, is obtained by multiplying the dry air mass flow by the corresponding humidity x (Eq. 4.93). As a basic quantity in humid air mass and energy balance calculations, we use dry air mass flow m and the effect of humidity on the energy balance is noted in the enthalpy h, (Eq. 4.87). 

Fig. 7.75, at a rate oi q, = mVs at 10 °C, corresponding to an air mass flow of 1.25 Fg/s, The same air mass flow is allowed to escape through the opening in the ceiling. This corresponds to a temperature increase of AG = 4 C. 7 t what height will the interface between the fresh bottom layer and the upper recirculation layer stabilize ... 

Room air currents favorable to capture Contaminants of low toxicity or of nuisance value only Intermittent, low production Large hood large air mass in motion... 

The zoning of the space is based on the assumption of constant temperature, concentration, and humidity in each separate zone." - The boundaries between the zones can be vertical or horizontal. The balances for air mass flow, contaminant mass flow, water vapor mass flow, and beat flow arc determined between zones and between zone and outer boundaries. 

In the stratification strategy with a replacing air distribution in the lower zone, the height of the boundary layer between the lower and upper zones can be determined with the criteria of the contaminant interfacial level.This level, where the air mass flow in the plumes is equal to the air mass flow of the supply air, IS presented in Fig. 8,4. In this ideal case the wait and air temperatures are equal on the interfacial level. In practical cases they are not usually equal and the buoyancy flows on the walls will raise the level and decrease the gradient. 

The calculation of the two-zone model is based on the balance equations for air mass flow, contaminant mass flow, water vapor mass flow, and heat flow of both zones. 

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