Test: Properties of Moist Air - 2 - Mechanical Engineering MCQ

Assuming that the dry air and water vapour behaves as perfect gases, we have for dry 

For water vapour

Also


R_a = 0.287 kJ/kgK (for dry air)
R_v = 0.461 kJ/kgK (for water vapour)

Mass of water vapour present per m³ of dry air is called absolute humidity.

Dew point temperature (DPT):

• It is a temperature at which moisture present in the atmosphere starts condensing or it is the temperature at which the first droplet of moisture is formed.
• As we know that for each pressure air has a specific saturation temperature, therefore for fully saturated air DBT, WBT and DPT are equal.

• When the relative humidity of the air is 100%, i.e the air is saturated, the dew point temperature (DPT) equals the wet-bulb temperature (WBT), which is also equal to the dry-bulb temperature.

Dew point temperature is the temperature of air recorded by a thermometer, when the moisture (water vapour) present in it begins condense.
In other words dew point temperature is the saturation temperature corresponding to the, partial pressure of water vapour.

For saturated air, dry bulb temperature, wet bulb temperature and dew point temperature are same

For a mixture of air and water vapour.

Degree of saturation is the ratio of actual specific humidity to the specific humidity under saturated condition.

WBT and specific humidity increases