Pounds Per Square Inch Gauge

What is Pressure level

Pressure is a measure out of the force exerted per unit area on the boundaries of a substance. The standard unit of measurement for pressure in the SI system is the Newton per foursquare meter or pascal (Pa). Mathematically:

p = F/A

where

• p is the pressure
• F is the normal force
• A is the expanse of the purlieus

Pascal is defined as a force of 1N that is exerted on a unit expanse.

• 1 Pascal = one N/m^two

However, for nearly engineering problems it is fairly minor unit, so it is convenient to work with multiples of the pascal: the kPa, the bar, and the MPa.

• i MPa  ten⁶ Due north/one thousand^two
• 1 bar    ten^five Due north/grand²
• 1 kPa   ten³ N/grand²

In full general, pressure or the force exerted per unit area on the boundaries of a substance is caused by the collisions of the molecules of the substance with the boundaries of the system. As molecules hit the walls, they exert forces that endeavor to push the walls outward. The forces resulting from all of these collisions cause the force per unit area exerted by a system on its surroundings. Pressure level equally an intensive variable is constant in a closed system. It is only relevant in liquid or gaseous systems.

Pounds per foursquare inch – psi

The standard unit in the English system is the pound-force per square inch (psi). It is the pressure resulting from a force of ane pound-strength applied to an area of ane square inch.

• 1 psi  1 lbf/inⁱⁱ = 4.45 North / (0.0254 m)² ≈ 6895 kg/m²

Therefore, i pound per square inch is approximately 6895 Pa.

The unit of measurement chosen standard atmosphere (atm) is divers as:

• 1 atm = 14.7 psi

The standard atmosphere approximates the average force per unit area at sea level at the latitude of 45° N. Note that at that place is a divergence between the standard atmosphere (atm) and the technical atmosphere (at).

A technical atmosphere is a non-SI unit of pressure equal to i kilogram-forcefulness per foursquare centimeter.

• 1 at = 14.two psi

See besides: Pascal – Unit of Force per unit area

Meet also: Bar – Unit of Pressure

Come across besides: Typical Pressures in Engineering

Absolute vs. Gauge Pressure

Pressure, equally discussed above, is called accented pressure level. Often it volition be important to distinguish between absolute pressure and approximate force per unit area. In this article, the term pressure level refers to absolute pressure unless explicitly stated otherwise. But in engineering, nosotros often deal with pressures that are measured by some devices. Although absolute pressures must exist used in thermodynamic relations, pressure-measuring devices often indicate the difference between the accented pressure in a system and the accented pressure of the atmosphere existing exterior the measuring device. They measure the approximate pressure level.

• Accented Pressure. When pressure is measured relative to a perfect vacuum, it is called absolute pressure (psia). Pounds per square inch accented (psia) is used to analyze that the force per unit area is relative to a vacuum rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is effectually 101.3 kPa (14.7 psi), this will be added to whatever force per unit area reading fabricated in air at sea level.
• Judge Pressure. When pressure level is measured relative to atmospheric pressure level (14.7 psi), gauge pressure (psig), the term guess pressure is practical when the pressure level in the system is greater than the local atmospheric pressure, p_atm. The latter force per unit area scale was developed because near all pressure gauges register goose egg when open to the temper. Gauge pressures are positive if they are to a higher place atmospheric pressure and negative if they are below atmospheric force per unit area.

p _gauge = p _absolute – p _{absolute; atm}

• Atmospheric Force per unit area. Atmospheric pressure is the pressure in the surrounding air at – or "close" to – the world'due south surface. The atmospheric pressure varies with temperature and altitude above sea level. The Standard Atmospheric Pressure approximates to the boilerplate pressure at body of water-level at the latitude 45° N.  The Standard Atmospheric Pressure is defined at sea-level at 273 ^o K (0 ^o C) and is:
  • 101325 Pa
  • one.01325 bar
  • 14.696 psi
  • 760 mmHg
  • 760 torr
• Negative Gauge Force per unit area – Vacuum Pressure level. When the local atmospheric pressure level is greater than the pressure level in the organization, the term vacuum pressure is used. A perfect vacuum would correspond to absolute cipher pressure. It is certainly possible to take a negative gauge pressure level just not possible to accept negative accented force per unit area. For instance, an accented force per unit area of lxxx kPa may be described as a gauge pressure of −21 kPa (i.due east., 21 kPa below atmospheric force per unit area of 101 kPa).

p _vacuum = p _{accented; atm} – p _absolute

For example, a auto tire pumped upwardly to 2.v atm (36.75 psig) higher up local atmospheric pressure (permit say 1 atm or 14.7 psia locally), volition have an absolute pressure level of 2.v + 1 = 3.five atm (36.75 + 14.7 = 51.45 psia or 36.75 psig).

On the other hand condensing steamturbines (at nuclear power plants) exhaust steam at a force per unit area well below atmospheric (e.g., at 0.08 bar or 8 kPa or ane.16 psia) and in a partially condensed country. In relative units it is a negative gauge pressure of virtually – 0.92 bar, – 92 kPa, or – 13.54 psig.

References:

Reactor Physics and Thermal Hydraulics:

1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Technology, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
3. Due west. 1000. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Applied science, Springer; 4th edition, 1994, ISBN: 978-0412985317
5. Todreas Neil Eastward., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, 2d Edition. CRC Printing; ii edition, 2012, ISBN: 978-0415802871
6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Establish Systems. Springer; 2015, ISBN: 978-3-319-13419-2
7. Moran Michal J., Shapiro Howard N. Fundamentals of Applied science Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
9. U.Due south. Department of Free energy, THERMODYNAMICS, Estrus TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume one, 2, and 3. June 1992.

Pounds Per Square Inch Gauge,

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