Wet-bulb temperature

Temperature read by a thermometer covered in water-soaked cloth

Wet-bulb temperature

The wet-bulb temperature is a measure of the lowest temperature that can be reached under current ambient conditions by the evaporation of water only. It is an important metric in meteorology, climatology, and thermodynamics because it reflects the cooling effect of evaporation, which is a key process in the water cycle and in human thermoregulation.

A sling psychrometer, used to measure wet-bulb temperature

Measurement

The wet-bulb temperature is typically measured using a device called a psychrometer, which consists of two thermometers: a dry-bulb thermometer and a wet-bulb thermometer. The wet-bulb thermometer is covered with a water-soaked cloth, and as water evaporates from the cloth, it cools the thermometer. The difference in readings between the dry-bulb and wet-bulb thermometers can be used to calculate the relative humidity and dew point.

Importance in Meteorology

In meteorology, the wet-bulb temperature is crucial for understanding the heat index, which combines air temperature and humidity to estimate the perceived temperature. It is also used to assess the risk of heat stress in humans and animals, as high wet-bulb temperatures can indicate conditions where the body cannot effectively cool itself through sweating.

Applications

Wet-bulb temperature is used in various fields:

• Agriculture: It helps in determining the potential for crop evapotranspiration and irrigation needs.
• HVAC systems: It is used to design and evaluate the efficiency of air conditioning systems.
• Sports and Occupational Safety: It is used to assess the risk of heat-related illnesses during physical activities and in workplaces.

A wet-dry hygrometer, another instrument for measuring wet-bulb temperature

Calculation

The wet-bulb temperature can be calculated using various formulas and approximations, depending on the available data and required accuracy. One common method involves using a psychrometric chart, which graphically represents the relationships between air temperature, wet-bulb temperature, relative humidity, and other properties of moist air.

Related pages

• Dew point
• Relative humidity
• Heat index
• Psychrometrics