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Holsoft's Physics Resources Pages

Physical properties of air

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properties listed below:
general    viscosity    density   

To calculate relative humidity from dry-bulb and wet-bulb temperatures,
try our Relative Humidity Calculator

general physical properties of air        [top]
quantity value
density (T=273 K) 1.29 kg/m3
viscosity (T=273 K) 17.1 x 10-6 Pa s
specific heat at constant pressure (cp; T=273 K) 1000 J kg-1 K-1
ratio cp / cV (T=273 K) 1.40
heat conductivity (T=273 K) 0.024 W m-1 K-1
melting point (approx; p=p0) 60 K
boiling point (approx; p=p0) 80 K
melting heat (approx) 2.1 x 105 J/kg
critical temperature (approx) 132 K
critical pressure (approx) 3.8 x 106 Pa
inversion temperature (approx) 659 K
speed of sound 331 m/s     (T=273 K)
340 m/s     (T=293 K)
relative permittivity r (T=273 K; p=p0) 1.0006
index of refraction
(relative to vacuum)
1.00029     (589 nm; T=273 K; p=p0)



viscosity of air   (online calculator)        [top]
The viscosity of air, as a function of temperature, is well described by the following empirical equation, with air temperature T in Celcius [oC] and viscosity in Pascal-seconds [Pa.s]:
some spaceequ: viscosity of air
Error: <0.1x10-6 Pa.s; validity range: 0-54oC.
[Source: parabolic fit on values from CRC Handbook, 1986; Weast (Ed.); page F-42]


density of humid air   (online calculator)        [top]
The density of humid air, as a function of temperature, barometric pressure and partial vapour pressure, is well described by the following empirical equation:
some spaceequ: density of air
T: absolute temperature [K]; B: barometric pressure [Pa]; pv: partial pressure of water vapour [Pa]; density in [kg/m3]. NB: saturated vapour pressures can be found here.
[Adapted from: CRC Handbook, 1986; Weast (Ed.); page F-8]

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