The pressure in a fluid is defined as:
“The normal force per unit of area exerted on an imaginary or real flat surface in a fluid or gas”
The pressure equation can be expressed as:
p = F / A (1)
Where
p = pressure (lb/in 2 (psi), lb/ft 2 (psf), N/m 2 , kg/ms 2 (Pa))
F = strength (n) 1)
A = Area (in 2 , feet 2 , m 2 )
1) In Imperial - Englying Engineering System, special care should be taken with the power unit. The basic mass unit is slug and the unit for strength is pound ( lb ) or pound strength ( lb f ).
Absolute pressure
A absolute pressure – p abs - It is measured in relation to the pressure of the zero absolute - The pressure that would occur in the absolute vacuum. All calculations involving gas law require pressure (and temperature) to be absolute units.
Manometric pressure
One meter It is often used to measure the pressure difference between a system and the surrounding atmosphere. This pressure is often called grueling and can be expressed as
p g = p s – p atm (2)
Where
p g = Manometric pressure (PA, psi)
p s = System pressure (PA, psi)
p atm = atmospheric pressure (PA, psi)
Atmospheric pressure
Atmospheric pressure is the surrounding air pressure - or "close" - from the earth's surface. Atmospheric pressure varies with temperature and altitude above sea level.
- Air density at altitude
Standard atmospheric pressure
A Standard atmospheric pressure ( atm ) It is usually used as a reference to list densities and gas volumes. Standard atmospheric pressure is defined at sea level 273 o K (0 o C) And it is 1,01325 bar or 101325 PA (Absolute) . The temperature of 293 o K (20 o C) Sometimes it is used.
In imperial units, standard atmospheric pressure is 14,696 psi.
- 1 atm = 1,01325 bar = 101,3 kPa = 1,013 10 5 Pa = 14,696 psi (lb f /in 2 )= 760 mmHg = 10,33 mH 2 O = 760 tor = 29,92 Inhg = 1013 mbar = 1,0332 kg f /cm 2 = 33,90 ftH 2o _
Pressure units
As 1 Pa It is a small unit of pressure, the hectoposcal unit (HPA) is widely used, especially in meteorology. The Kilopascal Unit (KPA) is commonly used in the design of technical applications - such as HVAC systems, piping systems and the like.
- 1 hectoPascal = 100 Pascal = 1 milibar
- 1 kiloPascal = 1000 Pascal
Some levels of pressure
- 10 Pa - The pressure below 1 mm of water
- 1 kPa - Approximately the pressure exerted by 10 g mass in an area of 1 cm 2
- 10 kPa - The pressure below 1 m of water, or the drop in air pressure over sea level to 1000 m of altitude
- 10 MPa - Beak pressure in a “high pressure” washing machine
- 10 GPa - enough pressure to form diamonds
Some alternative pressure units
- 1 bar - 100,000 Pa
- 1 Milibar - 100 Pa
- 1 atmosphere - 101325 PA
- 1 mm Hg – 133 Pa
- 1 inch hg - 3386 PA
One torr (Often used in vacuum applications) is named Torricelli and is the pressure produced by a mercury column 1 mm the height - equal to 1/760 of an atmosphere.
- 1 atm = 760 torr = 14,696 psi = 1,013 bar
Pounds by square inch (psi) It was commonly used in the UK, but is now replaced in almost every country except in the US units. How atmospheric pressure is of 14,696 psi - An air column in an area of a square inch from the earth's surface to space - weighs 14,696 pounds .
A barra (barra) It is commonly used in industry. A bar is 100.000 Pa and, for practical purposes, can be approximated to an atmosphere even if
1 bar = 0,9869 atm = 14,5 psi
They exist 1000 milibares (mbar) em a bar , a common unit in meteorology and meteorological applications.
1 milibar = 0,001 bar = 0,750 torr = 100 Pa
Source: https://www.engineeringtoolbox.com/pressure-d_587.html
