Wet Bulb Dry Bulb Humidity

Air humidity can be estimated by measuring.

Wet bulb dry bulb humidity.

The difference between these two temperatures is a measure of the humidity of the air. 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 wbt is the temperature read by a thermometer covered in water soaked cloth wet bulb thermometer over which air is passed.

The depression in wet bulb temperature allows the humidity to be calculated. 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. 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. A wet cloth is placed over the bulb of a thermometer and then air is blown over the cloth causing the water to evaporate.

Dry bulb temperature t db can be measured with a simple thermometer as shown above. Since evaporation takes up heat the thermometer will cool to a lower temperature than a thermometer with a dry bulb at the same time and place. Dry bulb temperature and. At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling.

Note that continuously air flow around the thermometer is important to evaporate. The dry bulb temperature is the ambient temperature. Given the wet bulb temperature dry bulb temperature and ambient pressure the humidity of the air can be calculated as follows.