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Values are given in terms of temperature necessary to reach the specified pressure. 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).
Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures.Liquid helium may show superfluidity.. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temperature of −269 °C (−452.20 °F; 4.15 K).
2 He helium; use: 4.222 K: −268.928 °C: −452.07 °F WebEl: ... Unless noted, all values refer to the normal boiling point at standard pressure (101.325 kPa ...
Helium remains liquid down to absolute zero at atmospheric pressure, but it freezes at high pressure. Solid helium requires a temperature of 1–1.5 K (about −272 °C or −457 °F) at about 25 bar (2.5 MPa) of pressure. [107] It is often hard to distinguish solid from liquid helium since the refractive index of the two phases are nearly the same
ref T c (K) T c (°C) P c (MPa) P c (other) V c (cm 3 /mol) ρ c (g/cm 3) ; 1 H hydrogen; use: 32.97: −240.18: 1.293: CRC.a: 32.97: −240.18: 1.293: 65: KAL: 33.2: 1.297: 65.0: SMI: −239.9: 13.2 kgf/cm 2: 0.0310 1 H hydrogen (equilibrium)
A typical phase diagram.The solid green line applies to most substances; the dashed green line gives the anomalous behavior of water. In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. [1]
The lowest pressure at which He-I and He-II can coexist is the vapor−He-I−He-II triple point at 2.1768 K (−270.9732 °C) and 5.0418 kPa (0.049759 atm), which is the "saturated vapor pressure" at that temperature (pure helium gas in thermal equilibrium over the liquid surface, in a hermetic container). [1]
A Assuming an altitude of 194 metres above mean sea level (the worldwide median altitude of human habitation), an indoor temperature of 23 °C, a dewpoint of 9 °C (40.85% relative humidity), and 760 mmHg sea level–corrected barometric pressure (molar water vapor content = 1.16%). B Calculated values *Derived data by calculation.