Wet Bulb Dry Bulb

By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only.

Wet bulb dry bulb.

Wet bulb temperature is the lowest temperature to which air can be cooled by the evaporation of water into the air at a constant pressure. 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 dry bulb wet bulb and dew point temperatures are important to determine the state of humid air. 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.

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. 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. At 100 relative humidity the wet bulb temperature is equal to the air temperature dry bulb temperature. The uncovered thermometer measures dry bulb temperature while the one covered with wet cloth measures wet bulb temeprature.

Combining the dry bulb and wet bulb temperature in a psychrometric diagram or mollier chart gives the state of the humid air. 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. At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling. The dry bulb temperature is the ambient temperature.