Dry Bulb Temperature °Cdb
Temperature of air as measured by a standard thermometer with a dry sensing bulb.
Temperature (dry bulb) is always shown on a standard psychrometric chart.
Wet Bulb Temperature °Cwb
Temperature of air as measured by a thermometer using a sensing bulb covered by a wet wick. As the thermometer is moved through the air, water will evaporate from the wick at a rate determined by the relative humidity of the surrounding air. As the water evaporates, latent heat is adsorbed from the wick which lowers the bulb temperature. The drier the air the more the thermometer cools and hence, the lower the wet-bulb reading.
At 100% RH there would no moisture evaporation from the wick (therefore no cooling effect) so the wet bulb temperature would be the same as dry bulb temperature.
Temperature (wet bulb) is always shown on a standard psychrometric chart.