What are dry-bulb temperature and wet-bulb temperature?

This post was last edited by ylb913 on 2015-8-22 at 10:46. Dry-bulb temperature is the atmospheric temperature under actual atmospheric humidity; this is what we commonly refer to as air temperature. The wet-bulb temperature is easy to understand once you look at a “wet-bulb thermometer”. What does the temperature difference between the two represent? The dry-bulb temperature is the actual temperature of the air in contact with the surface of the bulb, while the wet-bulb temperature is the temperature of the bulb when water is present on its surface; the evaporation of water removes heat from the bulb. The amount of water that evaporates depends on the humidity of the air – the higher the humidity, the less water evaporates and the less heat is removed, resulting in a smaller difference between the dry-bulb and wet-bulb temperatures ； The lower the air humidity, the greater the rate of water evaporation, and thus the more heat is carried away. This results in a larger temperature difference between the dry and wet bulbs. Therefore, the pattern of changes in this temperature difference can be used to indicate the current level of air humidity.

Dry-bulb temperature is the temperature measured by a thermometer in normal air, which is what we usually refer to as the air temperature in weather forecasts. The wet-bulb temperature refers to the air temperature at which the water vapor in the air reaches saturation under conditions of the same enthalpy; on an air enthalpy-humidity diagram, it is the dry-bulb temperature of the point corresponding to the position where the air condition point moves along the isenthalpy line down to the 100% relative humidity line. Wrap the temperature-sensing part of a regular thermometer with a wet gauze pad; the lower end of the gauze should be submerged in water to keep the air humidity around that area saturated. Ensure adequate air circulation around the gauze so that the air surrounding it is nearly isenthalpic. Once the reading stabilizes, the value shown on the thermometer can be considered approximately the wet-bulb temperature.

The dry-bulb temperature is the temperature measured directly with a thermometer, while the wet-bulb temperature is the temperature measured when the air is saturated