Water Vapor Air

Overview

Engineering reference data for Water Vapor Air in air psychrometrics.

Key Formulas

Humidity Ratio

$\omega = 0.622 \frac{P_v}{P_a}$

Mass of water vapor per mass of dry air.

Relative Humidity

$\phi = \frac{P_v}{P_{vs}} \times 100\%$

Ratio of actual to saturation vapor pressure.

Wet Bulb Temperature

$T_{wb} = T_{db} - \frac{P_{vs} - P_v}{\gamma}$

Temperature measured by wet-bulb thermometer.

Enthalpy of Moist Air

$h = c_p T + \omega h_g$

Sensible + latent heat per unit mass of dry air.

Variables

Symbol	Description	Unit
$\omega$	Humidity ratio	kg/kg
$\phi$	Relative humidity	%
$P_v$	Vapor pressure	Pa
$P_{vs}$	Saturation vapor pressure	Pa
$T_{db}$	Dry bulb temperature	°C
$T_{wb}$	Wet bulb temperature	°C

Data Tables: Moisture Content in Air

The following tables provide the weight of water vapor in moist air at standard atmospheric pressure, presented in two common engineering units.

Grains of Water Vapor per Pound of Dry Air

Note: 1 grain = 0.000143 lbm = 0.0648 g (7000 grains per lbm).

Pounds of Water Vapor per Pound of Dry Air

Interactive Charts

References

• Original Source