Note that continuously air flow around the thermometer is important to evaporate.
Wet bulb dry bulb humidity.
Wet bulb temperature t wb can be measured with a standard thermometer with some wet clothing cotton or similar around the bulb.
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.
Given the wet bulb temperature dry bulb temperature and ambient pressure the humidity of the air can be calculated as follows.
Dry bulb temperature t db can be measured with a simple thermometer as shown above.
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.
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.
At 100 relative humidity the wet bulb temperature is equal to the air temperature dry bulb temperature.
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.
Dry bulb temperature and.
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.
When the psychrometer is swung around by its attached chain or handle the air causes the water on the wick to evaporate which.
By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only.
The difference between these two temperatures is a measure of the humidity of the air.