How Does a Sling Psychrometer Work?
Relative Humidity A psychrometer is a simple device for measuring the relative humidity of the air. At any temperature, the air is able to absorb a certain amount of water vapor. The relative humidity is a measurement of the portion of the total possible water vapor that is currently in the air. When the air is nearly completely filled with vapor, it feels muggy if the air is hot or damp if it is cold. Principles A sling psychrometer measures the humidity by measuring the cooling effect of evaporation. Water is constantly evaporating into the air and condensing out of it. When that water evaporates, it takes some of the heat from whatever it is evaporating off of with it, cooling that object down. That is why we sweat in the heat—to cool down. Water blowing past aids this evaporation, causing the object to cool more quickly when the air has a high relative humidity, however, water does not evaporate as easily. That is why humid days feel hotter than dry days—sweat doesn’t evaporate
