Absolute pressure is the true pressure of continuous masses (liquids, vapors and gases), measured from the absolute zero of pressure β absolute vacuum . The absolute zero pressure of macroscopic volumes of matter is practically unattainable, since any solid body forms pairs, and outer space also does not constitute an absolute void devoid of matter, since it contains hydrogen in the amount of several molecules per cubic centimeter.
There are also distinguished excess or gauge (instrument) pressure and environmental pressure (in terrestrial conditions β atmospheric pressure ). Overpressure is the difference in absolute pressure and ambient pressure. [1] . This difference can be both positive and negative. In the latter case, it is called rarefaction or vacuum, and excess pressure - residual. The measurement of absolute pressure in terrestrial conditions is associated with certain difficulties. The atmospheric pressure is practically measured with barometric devices, gauge pressure with pressure gauges, and the absolute pressure is calculated by the formula:
,
Where: β absolute pressure β atmospheric (barometric) pressure, β excess (gauge pressure). (In approximate technical calculations, instead of real atmospheric pressure, its value measured at sea level is used).
The equations of thermodynamics, gas laws, include only absolute pressure . Overpressure is also not a parameter of the thermodynamic system. [2] , [3]
Notes
- β Vukalovich M.P., Technical Thermodynamics, 1968 , p. 12.
- β Kirillin V.A., Technical Thermodynamics, 1983 , p. five.
- β Nashchokin V.V., Technical Thermodynamics and Heat Transfer, 1975 , p. 11-12.
Literature
- Vukalovich M.P.,. Technical thermodynamics. - Energy, 1968. - 496 p.
- Kirillin V.A. Technical Thermodynamics. - Energoatomizdat, 1983 .-- 416 p. .
- Nashchokin V.V. Technical Thermodynamics and Heat Transfer. - Higher school, 1975 .-- 496 p.