Dew Point and Relative Humidity

Dew Point and Relative Humidity Using a Sling Psychrometer

Sling Psychrometer • A double thermometer • One is ‘normal’ = dry bulb • One is covered with a wet piece of cloth = wet bulb • When water evaporates, it removes heat. • Therefore, the wet bulb will always record a lower temperature than the dry bulb. Wet Bulb Dry Bulb

Using the psychrometer • Wet the cloth at the end of one of the apparatus. • Carefully (!), gently (!), etc spin the psychrometer around for a few minutes. • Record the temperature of the dry bulb and the wet bulb in °C

Calculating Dew Point • Subtract the wet bulb temperature from the dry bulb temperature and record this value. • You should now have 3 values recorded: • Dry bulb ____ °C • Wet bulb ____ °C • Difference ____ °C

Calculating Dew Point, cont. • Open your ESRT to page 12. • Locate the dry bulb temperature on the vertical (left) axis of the Dew Point Temperature Chart. • Locate the difference between the wet and dry bulb temperature on the horizontal (top) of the chart. • Locate where the two values intersect: this is the dew point.

Calculating Relative Humidity (%) • Record and calculate the same three values as you did for dew point: • Dry bulb temp ___ °C • Wet bulb temp ___ °C • Difference ___ °C • Use the Relative Humidity chart on pg. 12 of your ESRT as you did for dew point. • The relative humidity is at the intersection of the dry bulb temperature and the difference values.

Dew Point and Relative Humidity