Properties of Water Vapor

The relative humidity of air is a measure of the absolute amount of moisture in the air.

The humid heat of an air-water vapor mixture is defined as the amount of heat required to raise the temperature of 1 kg dry air by 1 K.

The specific heat of dry air is 1.005 kJ/(kg dry air K).

The specific volume of air is typically expressed in units of cubic meter per kilogram (m3/kg) of dry air.

The humidity ratio is defined as the ratio of the mass of water vapour to the mass of dry air (kg water/kg dry air).

The relative humidity of air can be expressed as a ratio of the density of water vapour in the air to the density of saturated water vapour at the dry bulb temperature of air.

The humid heat of air is a measure of the amount of heat required to raise the temperature of 1 kg dry air by 1 K.

The specific volume of air is independent of the humidity ratio.

The density of saturated water vapour at the dry bulb temperature of air is always equal to the density of water vapour in the air.

The humid heat of an air-water vapor mixture is a constant value.