Wet Bulb Dry Bulb Humidity

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.

Wet bulb dry bulb humidity.

Given the wet bulb temperature dry bulb temperature and ambient pressure the humidity of the air can be calculated as follows. By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only. Air humidity can be estimated by measuring. At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling.

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 dry bulb temperature is the ambient temperature. 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. Note that continuously air flow around the thermometer is important to evaporate.

At 100 relative humidity the wet bulb temperature is equal to the air temperature dry bulb temperature. Dry bulb temperature t db can be measured with a simple thermometer as shown above. When the psychrometer is swung around by its attached chain or handle the air causes the water on the wick to evaporate which. Wet bulb temperature t wb can be measured with a standard thermometer with some wet clothing cotton or similar around the bulb.

The difference between these two temperatures is a measure of the humidity of the air. The depression in wet bulb temperature allows the humidity to be calculated. The higher the difference in these temperatures the lower is the humidity.