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Online Calculatorsback to 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: 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 wetbulb temperatures (T_{d} and T_{w}, respectively; Celcius scale), partial vapour pressure is calculated by (at ambient pressure 1 atm): where p_{sat,w} is saturated vapour pressure at the wetbulb temperature. Finally, saturated vapour pressure at drybulb 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=030^{o}C, error <0.1 kg/m^{3}: For a wider temperature range (T=050^{o}C, error <0.1 kg/m^{3}) use instead: Density _{w} in [kg/m^{3}]. (Note: at 3.98^{o}C water has its highest density). [Source: polynomial fit on values from Weast, 1986; page F10] density of (humid) air [top] Empirical relation: Temperature T in Celcius; barometric pressure B in [Pa]; partial vapour pressure p_{v} in [Pa]; _{a}: density [kg/m^{3}]; validity range: 'environmental' values. (Note: 1 atm = 1.01325 x 10^{5} Pa) [Source: Weast, 1986; page F8; modified for SI units] diffusion coefficient of water vapour in air [top] Empirical relation: T: temperature, Celcius [C]; D_{v}: diffusion coefficient [m^{2}/s]. Error: <0.1x10^{6} m^{2}/s; validity range: 045^{o}C. [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: 054^{o}C. [Source: parabolic fit on values from Weast, 1986; page F42]  
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