Scale height pressure

Scale height The decay constant assuming an exponential decay in pressure and temperature with height in a planet s atmosphere. 

The convective turbulence tend to dissipate large scale shears (wave length a > pressure scale height H ). The rate of dissipation... 

Prediction 3 is a consequence of high molar mass. The scale height of a gas in a gravitational field is that height for which its pressure decreases by 1/e. In the perfect-gas approximation, it is given by h — RT/gm, where rn is the molar mass of... 

Downcomer aeration factor prediction. The fractional liquid holdup varies from about 0.3 in the froth zone to close to unity in the clear liquid zone (Fig. 6.12a). The height of each zone is a complex function of system properties, operating conditions, and downcomer geometry. This makes it practically impossible to theoretically predict the average downcomer aeration factor <(>. . Correlations in the literature (e.g., 46) are based on limited data obtained in atmospheric pressure simulator work with small downcomers. It is therefore difficult to recommend them for commercial-size applications. Zuiderweg (17) presented a plot of downcomer aeration factors derived theoretically from commercial-scale high-pressure flood data. However, the plot is based on a handful of data and is therefore difficult to recommend for general aeration factor prediction. 

Fig. 3.2 The vertical structure of the atmosphere and associated temperature and pressure variation. Note the logarithmic scale for pressure. The inset shows gas concentration as a function of height in the heterosphere and illustrates the presence of lighter gases (hydrogen and helium) at greater heights.

Altitude (km) Temperature (K) Scale Height (km) Pressure (hPa) Concentration (cm-3) Potential Temperature(2) (K)... 

The first Table provides an estimate of the geometric height z (km), the atmospheric pressure p (hPa), the absolute temperature T (K), the atmospheric scale height H (km) and the air number density n (cm-3). 

Mean formula weight. Pressure scale height. Column density. Properties given at the 1 bar pressure level. Observed P-T profiles are adiabatic below the tropopauses. assuming0.80, - 0.19, andX= 0.01. 

The total number concentration of air as a function of altitude falls off approximately with the scale height H of atmospheric pressure ... 

In the lower atmosphere, the scale height H is about 8 km atT = 273 K. It is sometimes stated that the -folding length scale for pressure in the lower atmosphere is approximately 8 km (actually 1 km). 

The water photolysis under low O2 pressure always led to a loss of hydrogen into space. The diffusion rate of the H2 (or H after it has been broken down by photolysis) through the homopause and exobase is limited. The definition of the homopause (80-90 km altitude) is the point at which the molecular and eddy diffusion coefficients are equal or, in other words, the critical level below which an atmosphere is well-mixed. The exobase ( 550 km) is the height at which the atmosphere becomes collisionless above that height the mean free path of the molecules exceeds the local scale height (RTIg). 

This equation is called the barometric equation by geophysicists (i.e., aerologists and meteorologists) because it provides the absolute pressure in an air column for a given geometric elevation (i.e., altitude, Z), and in this particular case the reference elevation is taken equal to 0 meters (i.e., on Earth, the sea level is the datum plane). Usually, the factor denoted H = RT/Mg is named the scale height and it is expressed in m. It corresponds to the elevation at which the absolute gas pressure is divided by the Naperian base e = 2.718281828... 

Example If we assume, in a first approximation, air to be an ideal gas, having the average molar mass M = 28.930 x 10 kg.moT , a mass density / = 1.293 kg.m at T= 273.15 K, the scale height is equal to about 7.986 km. This means that for an altitude equal to that of Mount Everest (8.846 km), the absolute pressure is roughly a third of pressure exerted at sea level ... 

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