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The torr is defined as 1 / 760 of one standard atmosphere, while the atmosphere is defined as 101325 pascals. Therefore, 1 Torr is equal to 101325 / 760 Pa. The decimal form of this fraction ( 133.322 368 421 052 631 578 947 ) is an infinitely long, periodically repeating decimal ( repetend length: 18).
The Antoine equation [3] [4] is a pragmatic mathematical expression of the relation between the vapor pressure and the temperature of pure liquid or solid substances. It is obtained by curve-fitting and is adapted to the fact that vapor pressure is usually increasing and concave as a function of temperature. The basic form of the equation is:
Valid results within the quoted ranges from most equations are included in the table for comparison. A conversion factor is included into the original first coefficients of the equations to provide the pressure in pascals (CR2: 5.006, SMI: -0.875). Ref. SMI uses temperature scale ITS-48.
The Antoine equation is a class of semi-empirical correlations describing the relation between vapor pressure and temperature for pure substances. The Antoine equation is derived from the Clausius–Clapeyron relation. The equation was presented in 1888 by the French engineer Louis Charles Antoine (1825–1897). [1]
Examples of modern use of these formulae can additionally be found in NASA's GISS Model-E and Seinfeld and Pandis (2006). The former is an extremely simple Antoine equation, while the latter is a polynomial. [8] In 2018 a new physics-inspired approximation formula was devised and tested by Huang [9] who also reviews other recent attempts.
At standard mean sea level it specifies a temperature of 15 °C (59 °F), pressure of 101,325 pascals (14.6959 psi) (1 atm), and a density of 1.2250 kilograms per cubic meter (0.07647 lb/cu ft). It also specifies a temperature lapse rate of −6.5 °C (−11.7 °F) per km (approximately −2 °C (−3.6 °F) per 1,000 ft).
1.5 psi Decrease in air pressure when going from Earth sea level to 1000 m elevation [citation needed] +13 kPa +1.9 psi High air pressure for human lung, measured for trumpet player making staccato high notes [48] < +16 kPa +2.3 psi Systolic blood pressure in a healthy adult while at rest (< 120 mmHg) (gauge pressure) [44] +19.3 kPa +2.8 psi
An example of this is the air pressure in an automobile tire, which might be said to be "220 kPa (32 psi)", but is actually 220 kPa (32 psi) above atmospheric pressure. Since atmospheric pressure at sea level is about 100 kPa (14.7 psi), the absolute pressure in the tire is therefore about 320 kPa (46 psi).