Wet Bulb Dry Bulb

Relative humidity is measured using a device called a sling psychrometer this consists of 2 side by side conventional thermometers one of which the wet bulb thermometer has a wetted wick placed at the bottom the other the dry bulb thermometer has no wetted wick.

Wet bulb dry bulb. By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only. When the psychrometer is swung around by its attached chain or handle the air causes the water on the wick to evaporate which. The wet bulb temperature is always lower than the dry bulb temperature but will be identical with 100 relative humidity the air is at the saturation line. It includes a dry bulb thermometer a wet bulb thermometer and a psychrometric chart a graph that plots the relationships between the dry and wet bulb temperature relative humidity and dew point at constant pressure.

The dry bulb temperature is the ambient temperature. The wet bulb temperature wbt is the temperature read by a thermometer covered in water soaked cloth wet bulb thermometer over which air is passed. The uncovered thermometer measures dry bulb temperature while the one covered with wet cloth measures wet bulb temeprature. Since both the thermometers are placed side by side the mositure from wet wick may affect the readings of dry bulb thermometer to avoid this the wet bulb thermometer is placed at the lower level.

The dry bulb wet bulb and dew point temperatures are important to determine the state of humid air. Combining the dry bulb and wet bulb temperature in a psychrometric diagram or mollier chart gives the state of the humid air. It is therefore measured by wrapping a wet wick around the bulb of a thermometer and the measured temperature corresponds to the wet bulb temperature. The knowledge of only two of these values is enough to determine the state of the moist air including the content of water vapor and the sensible and latent energy enthalpy in the air.