wet bulb temperature

Wet bulb temperature is measured when using a sling psychrometer to determine relative humidity. A standard thermometer is used, with the thermometer bulb wrapped in cloth, which is kept wet. The evaporation of water from the thermometer has a cooling effect, so the temperature indicated by the wet bulb thermometer is less than the temperature indicated by a dry bulb (normal, unmodified) thermometer. The rate of evaporation from the wet bulb thermometer depends on the humidity of the air (evaporation is slower when the air is already full of water vapor). For this reason, the difference in the temperatures indicated by the two thermometers gives a measure of relative humidity.

Last modifed Monday, December 18, 2006.