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# Moist Air - Specific vs. Relative Humidity

## Specific humidity of moist air vs. relative humidity, water vapor and air density.

Humidity is the quantity of water vapor present in air. It can be expressed as an absolute, specific or a relative value.

If we know the relative humidity of the moist air and the water vapor density and the density of the air, the specific humidity can be expressed as:

x = 0.622 φ ρws / (ρ - ρws) 100%                               (1)

where

x = specific humidity (humidity ratio) of air vapor mixture (kgh2o/kgdry_air)

φ = relative humidity (%)

ρws = density of water vapor (kg/m3)

ρ = density of the moist or humid air (kg/m3)

## Related Topics

• ### Air Psychrometrics

Moist and humid air calculations. Psychrometric charts and Mollier diagrams. Air-condition systems temperatures, absolute and relative humidities and moisture content in air.

## Related Documents

• ### Air - Absolute Humidity

Absolute humidity is the actual mass of water vapor present in the air water vapor mixture.
• ### Air - Humidity Ratio

The mass of water vapor present in moist air - to the mass of dry air.
• ### Humid Air and the Ideal Gas Law

Pressure, temperature and volume in a perfect ideal gas like moist air (air with water vapor).
• ### Mixing of Humid Air

The change in state wwhen mixing moist air - enthalpy, heat, temperature and specific humidity.
• ### Moist Air - Density vs. Water Content and Temperature

Density of the mix of dry air and water vapor - moist humid air.
• ### Moist Air - Enthalpy

Sensible and latent heat of moist air.
• ### Moist Air - Properties

Psychrometric table with humid air properties like saturation pressure, specific volume, enthalpy and entropy.
• ### Moist Air - Relative Humidity

Relative humidity in moist air is the ratio of partial vapor pressure to air pressure.
• ### Moist Air - Specific Volume

Specific volume of moist air is defined as the total volume of humid air per mass unit of dry air
• ### Recommended Relative Humidity

Recommended relative humidity level.

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## Citation

• The Engineering ToolBox (2004). Moist Air - Specific vs. Relative Humidity. [online] Available at: https://www.engineeringtoolbox.com/specific-relative-humidity-air-d_688.html [Accessed Day Month Year].

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8.21.8

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