Wet bulb temperature (WBT) is usually measured with a sling or aspirated psychrometer consisting of two mercury thermometers, one of which is wrapped with a wick around the mercury bulb. The other is used to measure dry bulb temperature. To use this instrument, the wick is saturated with clean water and the psychrometer is whirled for approximately 10 to 15 seconds. The process is repeated two or three times until there is no further temperature drop on the wicked thermometer.
It is recorded by thermometer having wet muslin cloth on its bulb. The temperature recorded is in general lower than dry-bulb temperature because of cooling effect of the evaporating water of wet muslin cloth. They are equal only when air is in saturation and no net evaporation of water from wet muslin cloth takes place. Wet-bulb temperature can never be higher than dry-bulb temperature.
From the definition point of view, it is defined as the temperature at which water vapour evaporating into the air can bring down the air in saturation adiabatically at that temperature. It is a measure of the evaporating capacity of the air. Its unit is degree C or kelvin (K).
From the definition point of view, it is defined as the temperature at which water vapour evaporating into the air can bring down the air in saturation adiabatically at that temperature. It is a measure of the evaporating capacity of the air. Its unit is degree C or kelvin (K).
Web bulb depression is noted as the difference between the wet bulb and the dry bulb temperatures. The difference happens as the wet wick thermometer is cooled down by the evaporation on the wick. The greater the wet-bulb depression (Tdb - Twb), the lower shall be the RH. The amount of evaporation is a direct indication of the moisture carrying capacity of the atmospheric air at that temperature.