Psychrometric constant

Relation of the partial pressure of water in air to temperature

The psychrometric constant relates the partial pressure of water in air to the air temperature. This lets one interpolate actual vapor pressure from paired dry and wet thermometer bulb temperature readings. psychrometric constant [kPa °C−1],P = atmospheric pressure [kPa], latent heat of water vaporization, 2.45 [MJ kg−1], specific heat of air at constant pressure, [MJ kg−1 °C−1], ratio molecular weight of water vapor/dry air = 0.622.

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