Given the wet bulb temperature dry bulb temperature and ambient pressure the humidity of the air can be calculated as follows.
Wet bulb dry bulb humidity.
At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling.
Wet bulb temperature t wb can be measured with a standard thermometer with some wet clothing cotton or similar around the bulb.
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.
By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only.
The dry bulb temperature is the ambient temperature.
The difference between these two temperatures is a measure of the humidity of the air.
Air humidity can be estimated by measuring.
A wet cloth is placed over the bulb of a thermometer and then air is blown over the cloth causing the water to evaporate.
The higher the difference in these temperatures the lower is the humidity.
When the psychrometer is swung around by its attached chain or handle the air causes the water on the wick to evaporate which.
Dry bulb temperature and.
The depression in wet bulb temperature allows the humidity to be calculated.
Dry bulb temperature t db can be measured with a simple thermometer as shown above.
Note that continuously air flow around the thermometer is important to evaporate.
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.