Wet bulb and Dew point temperature

Wet bulb temperature -: The wet bulb temperature is the temperature read by a thermometer covered in water-soaked cloth ( wet bulb thermometer ) over which air is passed. If the bulb of an ordinary thermometer is surrounded by a wick wetter with water and air passed around it ; water at surface will being to evaporate. The vaporisation takes heat -leatent heat of vaporisation and the wick is cooled . The temperature finally reached when cooling stops is known as wet bulb temperature. At wet bulb temperature,  the heat from the air to water surface equals the haet taken from the surface to vaporise water.

                  At 100 % relative humidity , the wet bulb temperature is equal to the air temperature ( dry bulb temperature) and it is lower at lower humidity. A wet bulb temperature indicates a temperature close to the true ( thermodynamic ) temperature. The wet bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only.

Dew point temperature -: The dew-point temperature is the temperature at which moisture will condense out of the air for a given specific humidity and pressure, as air moisture temperature is reduced. It is important to note that dew point temperature remains constant as long as there us no change in moisture. 

                   The dew-point temperature is always lower than Or equal to the air temperature. If the air temperature cools to the dew point, or if the dew point raises to equal the air temperature, then dew , fog or coouds being to form. At this point where the dew point temperature equals the air temperature, the relative humidity us 100%.

At 100% humidity, wet bulb temperature is equal to the dry bulb temperature. Drier is the air , more will be the difference between dry bulb and wet bulb temperature.