The standard atmosphere was originally defined as the pressure exerted by 760 mm of mercury at 0 ☌ (32 ☏) and standard gravity ( g n = 9.806 65 m/s 2). It is approximately equal to Earth's average atmospheric pressure at sea level. It is sometimes used as a reference pressure or standard pressure. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101 325 Pa. For the album by Justin Jarvis, see Atmospheres (album).
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For the television series on the Weather Channel, see Atmospheres (TV series). DOE Fundamentals Handbook, Volume 1, 2, and 3. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-7-0 Thermodynamics in Nuclear Power Plant Systems. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer 4th edition, 1994, ISBN: 978-0412985317 Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 8-1. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983). In relative units it is a negative gauge pressure of about – 0.92 bar, – 92 kPa, or – 13.54 psig. On the other hand condensing steam turbines (at nuclear power plants) exhaust steam at a pressure well below atmospheric (e.g., at 0.08 bar or 8 kPa or 1.16 psia) and in a partially condensed state. For instance, an absolute pressure of 80 kPa may be described as a gauge pressure of −21 kPa (i.e., 21 kPa below atmospheric pressure of 101 kPa).įor example, a car tire pumped up to 2.5 atm (36.75 psig) above local atmospheric pressure (let say 1 atm or 14.7 psia locally), will have an absolute pressure of 2.5 + 1 = 3.5 atm (36.75 + 14.7 = 51.45 psia or 36.75 psig). It is certainly possible to have a negative gauge pressure but not possible to have negative absolute pressure.
A perfect vacuum would correspond to absolute zero pressure. When the local atmospheric pressure is greater than the pressure in the system, the term vacuum pressure is used. Negative Gauge Pressure – Vacuum Pressure.The Standard Atmospheric Pressure is defined at sea-level at 273 o K (0 o C) and is: The Standard Atmospheric Pressure approximates to the average pressure at sea-level at the latitude 45° N. The atmospheric pressure varies with temperature and altitude above sea level. Atmospheric pressure is the pressure in the surrounding air at – or “close” to – the earth’s surface. Gauge pressures are positive if they are above atmospheric pressure and negative if they are below atmospheric pressure. The latter pressure scale was developed because almost all pressure gauges register zero when open to the atmosphere. When pressure is measured relative to atmospheric pressure (14.7 psi), gauge pressure (psig), the term gauge pressure is applied when the pressure in the system is greater than the local atmospheric pressure, p atm. Since atmospheric pressure at sea level is around 101.3 kPa (14.7 psi), this will be added to any pressure reading made in air at sea level. Pounds per square inch absolute (psia) is used to clarify that the pressure is relative to a vacuum rather than the ambient atmospheric pressure. When pressure is measured relative to a perfect vacuum, it is called absolute pressure (psia). Although absolute pressures must be used in thermodynamic relations, pressure-measuring devices often indicate the difference between the absolute pressure in a system and the absolute pressure of the atmosphere existing outside the measuring device. But in engineering, we often deal with pressures that are measured by some devices. In this article, the term pressure refers to absolute pressure unless explicitly stated otherwise. Often it will be important to distinguish between absolute pressure and gauge pressure. Pressure, as discussed above, is called absolute pressure.
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