Question

Explain the concept of dry bulb, wet bulb temperature. How they are measured?

Answer 1

Dry bulb temperature:

Temperature recorded by ordinary thermometer is called dry bulb temperature.

Measurement of DBT:

The temperature of air measured by an ordinary thermometer without cover of bulb by wet cloth.

Wet bulb temperature:

It is the temperature indicated by thermometer whose bulb is covered with cotton or muslin wire wetted with moisture.

Measurement of WBT: 

The temperature of air measured by an ordinary thermometer with cover of bulb by wet cloth or wick and is exposed to the air. The readings of Dry bulb and wet bulb temperatures are used to predict weather. A large difference between the readings of dry and wet bulb temperatures indicates a dry weather. A small difference indicates a sultry weather or possible rain. One condition for rain is abundance of water vapour in the atmosphere.

Answer 2

WET BULB TEMPERATURE

► Wet bulb temperature is the temperature recorded by thermometer when the bulb is enveloped by cotton wick saturated with water.

► The accuracy of a simple wet-bulb thermometer depends on how fast air passes over the bulb and how well the thermometer is shielded from the radiant temperature of its surroundings.

DRY-BULB TEMPERATURE

► The dry-bulb temperature is the temperature indicated by a thermometer exposed to the air in a place sheltered from direct solar radiation. The term dry-bulb is customarily added to temperature to distinguish it from wet-bulb and dew point temperature

Answer 3

Dry Bulb Temperature of Air (DBT)
The temperature of the air measured by the ordinary thermometer is called as the dry bulb temperature of air, commonly referred as DBT. When ordinary thermometer is exposed to the atmosphere, it indicates the dry bulb temperature, which is nothing but the atmospheric temperature.

Wet Bulb Temperature of Air (WBT):
The wet bulb temperature of air is also measured by the ordinary thermometer, but the only difference is that the bulb of the thermometer is covered by the wet cloth. Temperature of the ordinary air measured by the thermometer when it is covered by wet cloth or wick is called as the wet bulb temperature, commonly referred to as WBT. When the air comes in contact with the wet cloth it absorbs some moisture and gives up some heat, sue to which the temperature of the air reduces. This reduced temperature measured by the thermometer is called as the wet bulb temperature.

If the moisture content of the air is very low, it will give up more heat to the cloth and the wet bulb temperature of air will also be comparatively lower. On the other hand, if the moisture content of air is high it will loose lesser heat to the air and wet bulb temperature will be higher. The more is the moisture or water vapor content of the air more is the wet bulb temperature. Thus the wet bulb temperature indirectly indicates the moisture content present in the air or we can say that it is affected by the relative humidity of the air.

The wet bulb temperature of the air is always less than the dry bulb temperature of air. The difference between the DBT and WBT is called as wet bulb depression.