- 天同Lv 76 年前最愛解答
Wet bulb temperature (濕球溫度) is measured by a wet-bulb thermometer (濕球溫度計).
The principle of a wet-bulb thermometer is based on the evapouration of water during which latent heat is absorbed. A wet-bulb thermometer has a piece of cotton wrapped around the temperature sensitive region of the thermometer (this is the mercury bulb in a mercury-in-glass thermometer or the platinum sensor in a platinum thermometer. In fact, these are the two types of thermometer used by the Hong Kong Observatory in wet-bulb temperature measurement). The piece of cotton is dipped into a small vessel containing water, which wets the cotton piece.
The rate of evapouration of water in the cotton piece depends very much on the humidity of the surrounding air. When the humidity is high, the evapouration rate is slow. But when the surrounding air is dry, the evapouration rate is fast.
Because latent heat (潛熱) is absorbed by water in it changes from liquid to gas state. Hence during evapouration, much heat is absorbed from the cotton piece and lowers its temperature. The thermometer then records this temperature. This is the wet-bulb temperature.
The difference between the wet-bulb temperature and the dry-bulb temperature (乾球溫度)(measured by an ordinary thermometer) gives a measurement on which the relative humidity (相對濕度) of air is estimated.
2014-12-10 15:31:26 補充：
A: It is the water that requires latent heat to vapourize. The heat is absorbed by the water and which comes from the cotton wrap.
2014-12-10 15:34:33 補充：
A: As said above,the heat comes from the cotton and is given to the water to make it vapourize. Thus the cotton wrap loses heat and its temperature decreases. The thermometer records such decrease of temperature.
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