Note that continuously air flow around the thermometer is important to evaporate.
Wet bulb dry bulb humidity.
Dry bulb temperature and.
Air humidity can be estimated by measuring.
Dry bulb temperature t db can be measured with a simple thermometer as shown above.
Given the wet bulb temperature dry bulb temperature and ambient pressure the humidity of the air can be calculated as follows.
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 depression in wet bulb temperature allows the humidity to be calculated.
At 100 relative humidity the wet bulb temperature is equal to the air temperature dry bulb temperature.
The higher the difference in these temperatures the lower is the humidity.
At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling.
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.
Wet bulb temperature t wb can be measured with a standard thermometer with some wet clothing cotton or similar around the bulb.
The dry bulb temperature is the ambient 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.
The difference between these two temperatures is a measure of the humidity of the 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.