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Online Calculators
back to Dust Monitoring Equipment main menusaturated vapour pressure
relative humidity of air
density of water
density of (humid) air
diffusion coefficient of water vapour in air
viscosity of air
Note:
Temperatures on this page are on the Celcius scale. If you
are more familiar with Fahrenheits, you may want to see what a value in
Celcius would be in Fahrenheit: use our F/C Converter.
saturated vapour pressure (SVP) [top]
Saturated water vapour pressure in air; empirical relation:
Temperature T in Celcius [ = {Kelvin} - 273.15]); validity range roughly 0-80oC.
[Source: Monteith and Unsworth, 1990; some parameters slightly adjusted ]
relative humidity of air [top]
Relative humidity is the ratio of partial vapour pressure and saturated vapour pressure at ambient temperature:
If humidity is to be determined by dry- and wet-bulb temperatures (Td and Tw, respectively; Celcius scale), partial vapour pressure is calculated by (at ambient pressure 1 atm):
where psat,w is saturated vapour pressure at the wet-bulb temperature. Finally, saturated vapour pressure at dry-bulb temperature (i.e. normal ambient temperature) must be calculated, and the pressure ratio gives relative humidity.
[Source: calculator for saturated vapour pressure (see above) and relation between bulb temperatures and vapour pressures (List, 1958)]
density of water [top]
Empirical relation for T=0-30oC, error <0.1 kg/m3:
For a wider temperature range (T=0-50oC, error <0.1 kg/m3) use instead:
Density
w in [kg/m3].(Note: at 3.98oC water has its highest density).
[Source: polynomial fit on values from Weast, 1986; page F-10]
density of (humid) air [top]
Empirical relation:
Temperature T in Celcius; barometric pressure B in [Pa]; partial vapour pressure pv in [Pa];
a: density [kg/m3]; validity range:
'environmental' values. (Note: 1 atm = 1.01325 x 105
Pa)[Source: Weast, 1986; page F-8; modified for SI units]
diffusion coefficient of water vapour in air [top]
Empirical relation:
T: temperature, Celcius [C]; Dv: diffusion coefficient [m2/s].
Error: <0.1x10-6 m2/s; validity range: 0-45oC.
[Source: linear fit on values given by Gates, 1980 (Appendix 3)]
viscosity of air [top]
Empirical relation:
T: temperature, Celcius [C]; viscosity in Pascal x seconds [Pa.s]>.
Error: <0.1x10-6 Pa.s; validity range: 0-54oC.
[Source: parabolic fit on values from Weast, 1986; page F-42]
Holsoft (c) 2001