Steam Humid Air

Overview

Engineering reference data for Steam Humid 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

Water Vapor in Air Reference Data

Humidification Calculation

The required amount of steam or water to humidify air can be calculated from the difference in vapor content:

$\Delta w = w_{final} - w_{initial}$

Where:

• $\Delta w$ = Amount of water vapor required (kg per 100 m³)
• $w_{final}$ = Final vapor content at target temperature and humidity (kg per 100 m³)
• $w_{initial}$ = Initial vapor content at starting conditions (kg per 100 m³)

Unit Conversion Note

The table values represent vapor content in $\text{kg per 100 m}^3$ air volume. For calculations using humidity ratio $x$ (mass of water vapor per mass of dry air), convert using:

$x = \frac{w}{\rho_{air}} \quad \text{(kg/kg dry air)}$

Where $\rho_{air}$ is the air density at the actual temperature.

Interactive Charts

References

• Original Source