Sea level air pressure

TABLE 5.1 Seasonal Cycles of Sea Level Air Pressure, Zonal ( , Positive Eastward) and Meridional Wind Component (v, Positive Northward), Wind Speed Ivl and Its Squared and Cubic Values Representing the So-Called Energy and Turbulence Indices Where Available, the Standard Deviation is Given Behind the Mean Peak Values of Each Row Are Given in Bold... 

FIGURE 5.1 Daily sea level air pressure (hPa) at Warnemunde, averaged over 59 years (1947-2005). 

Fig 5.3. The latter result from differences in sea-level air pressure between the stations Gibraltar (Iberian Peninsula), Reykjavik (Iceland), and Oulu (Finland) for the period 1881-2002. Due to spatial smoothing and monthly averaging, this graph does not resolve the temporal details of the ice saint loop in April/May. Although the summer behavior... 

FIGURE 5.11 Modified scheme proposed by Albeit and Hagen (1997) for the atmospheric winter circulation over the northern Atlantic Ocean indicating two distinct modes of the North Atlantic Oscillation, which is described by the difference in sea-level air pressure ( Ap) between the Icelandic Low (7) and the Azores High (H)-. (a) I Ap (NAO) corresponds to intensified westerlies conveying warm/humid (W) air masses toward western Europe and reduced inflow of cold/dry (O Siberian air masses,(b) -Ap (NAO) corresponds to the opposite situation of (a). 

Performance tables are based on standard dry air at 70°F at sea level (barometric pressure 29.92 in. Hg) with a density of 0.075 lb per fp. When the fans are required to handle gases at other conditions at the inlet, corrections must be made for temperature, altitude, and air or gas density. 

BAROMETRIC PRESSURE, The pressure of the air at a particular point on or above the surface of the. earth. At sea level, this pressure is sufficient to support a column of mercury approximately 29.9 inches in height (760 mmi, equivalent to 14.7 lbs/inch2 absolute (psia) or 1 atm. 

Figure 18.3 is an Eh-pH diagram calculated for the system Mn — H2O-CO2 at 25°C and /coj = 10 atm (the CO2 partial pressure of normal sea-level air). It differs from Figure 18.2 for the system Mn — H2O only in the appearance of rhodochrosite, MnCOa, which swamps the fields of Mn(OH)2 and most of Mn304. The calculations are similar to those above, except that the following carbonate equilibria must be included. 

Assuming that air has a mean molar mass of 28.9 g/mol and that the atmosphere is isothermal at 25 °C, compute the barometric pressure at Denver, which is 1600 m above sea level compute the barometric pressure at the top of Mt. Evans, 4348 m above sea level. The pressure at sea level may be taken as 760 Torr. 

Pressure is an inherent quantity associated with air and the gases that compose it. At sea level, the pressure due to the thin blanket of gas that covers Earth is about 14.7 pounds per square inch. That pressure is a result of the constant collisions between air molecules and everything else. The layer of air that surrounds the Earth is called the a(moa diei and without it, we could not exist. Earth s atmosphere provides the oxygen we need to breathe and protects us from short-wavelength radiation that would otherwise kill us. It is responsible for wind, rain, red-colored sunsets, and blue-colored midday skies. If the atmosphere were suddenly removed, we would die within minutes in the dark vacuum of space. The gas that fills the air bag, nitrogen, is the same one that composes 80% of the atmosphere. In this chapter, we learn about both the atmosphere and the gases that compose it. 

At altitudes above sea level the percentage of oxygen in air is unaltered, but because the barometric pressure is less, the partial pressure of oxygen drops accordingly and makes breathing more difficult. At sea level barometric pressure equals 760 mm Hg, ffierefore oxygen partial pressure equals 760 X 21/100 = 160 mm Hg. ... 

Human evolution has taken place close to sea level, and humans are physiologically adjusted to the absolute partial pressure of the oxygen at that point, namely 21.2 kPa (159.2 mm Hg), ie, 20.946% of 101.325 kPa (760 mm Hg). However, humans may become acclimatized to life and work at altitudes as high as 2500—4000 m. At the 3000-m level, the atmospheric pressure drops to 70 kPa (523 mm Hg) and the oxygen partial pressure to 14.61 kPa (110 mm Hg), only slightly above the 13.73 kPa (102.9 mm Hg) for the normal oxygen pressure in alveolar air. To compensate, the individual is forced to breathe much more rapidly to increase the ratio of new air to old in the lung mixture. 

The theoretical steam rate (sometimes referred to as the water rate) for stream turbines can be determined from Keenan and Keyes or Mollier charts following a constant entropy path. The theoretical steam rate is given as Ib/hr/kw which is easily converted to Ib/hr/hp. One word of caution—in using Keenan and Keyes, steam pressures are given in PSIG. Sea level is the basis. For low steam pressures at high altitudes appropriate coirections must be made. See the section on Pressure Drop Air-Cooled Air Side Heat Exchangers, in this handbook, for the equation to correct atmospheric pressure for altitude. 

A corresponding situation occurs at high altitude, where one-third of the sea-level power available has been lost due to low atmospheric pressure. This low air density also reduces aerodynamic drag, but rolling resistance is unaffected by altitude. As a result, power resei"ve is seen to suffer. In fact, at this altitude, the power available in fourth gear is insufficient to operate the vehicle on a 6 percent grade at any speed without downshifting. 

If a column of air 1-inch square extended to the top of the atmosphere could be weighed, this column of air would weigh approximately 14.7 pounds at sea level. Thus, atmospheric pressure, at sea level, is approximately 14.7 pounds per square inch or psi. 

Atmospheric pressure decreases by approximately 1.0 psi for every 2343 feet of elevation. Elevations below sea level, such as in excavations and depressions, atmospheric pressure increases. Pressures under water differ from those under air only because the weight of the water must be added to the pressure of the air. 

Psychrometry has to do with the properties of the air-water vapor mixtures found in the atmosphere. Psychrometry tables, published by the US Weather Bureau, give detailed data about vapor pressure, relative humidity and dew point at the sea-level barometer of 30 in Hg, and at certain other barometric pressures. These tables are based on relative readings of dry bulb and wet bulb atmospheric temperatures as determined simultaneously by a sling psychrometer. The dry bulb reads ambient temperature while the wet bulb reads a lower temperature influenced by evaporation from a wetted wick surrounding the bulb of a parallel thermometer. 

Air at sea level exerts a static pressure, due to the weight of the atmosphere, of 1013.25 mhar. The density, or specific mass, at 20°C is 1.2 kg/m . Densities at other conditions of pressure and temperature can he calculated from the Gas Laws ... 

The air is said to be thinner in higher altitudes than at sea level. Compare the density of air at sea level where the barometric pressure is 755 mm Hg and the temperature is 0°C with the density of air on top of Mt. Everest at the same temperature. The barometric pressure at that altitude is 210 mm Hg (3 significant figures). Take the molar mass of air to be 29.0 g/mol. 

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