Humid Air Ideal Gas

Overview

Engineering reference data for Humid Air Ideal Gas 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

Air and Water Vapor Properties

Dalton's Law and Partial Pressures

Dalton's Law states that the total pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases. For moist air, this means the total pressure is the combined effect of dry air and water vapor. The partial pressures can be determined using the ideal gas law with the respective densities and gas constants.

Saturation Pressure

The saturation pressure, denoted as $p_{ws}$, is the maximum vapor pressure before water vapor begins to condense at a given temperature. In moist air, common vapor partial pressures range from 0.5 to 3.0 kPa, which is low compared to dry air partial pressure due to water's relatively high boiling point.

Interactive Charts

References

• Original Source