Equ 2.5 Dry bulb, wet bulb and dew point temperature

Unless otherwise specified, the temperature of an air-water vapour mixture is that temperature which is indicated by an or­dinary or dry-bulb thermometer. This dry-bulb temperature is the temperature of both the air and the water vapour in the mix­ture. The wet-bulb temperature may be determined by sub­merging a water-covered bulb in the air-water vapour mixture until equilibrium is obtained.

The wet-bulb temperature will be lower than the dry-bulb tem­perature as long as evaporation continues. If no evaporation is possible, the mixture is saturated and the wet and dry-bulb tem­peratures for this condition will be identical, the dew point tem­perature of an air-water vapour mixture is the saturation tem­perature corresponding to the absolute humidity of the mixture.

The dew point temperature may also be considered as that temperature at which condensation begins when the mixture is gradually cooled.

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