Sling Psychrometer

A sling psychrometer is a simple device used to determine the humidity in the air. It consists of two thermometers namely a wet bulb and a dry bulb. A psychrometer chart is also used in the process.

A Sling Psychrometer ⇫

Experiment Procedure:

• Note the temperature of both thermometers. The temperature should be the same for both thermometers. We got 25 °C for both thermometers.
• Wrap gauze around the bulb of one thermometer with the help of rubber bands. This is known as a wet bulb.
• Then bind both thermometers back to back via a string.
• Now dip the wet-bulb into the water so that the gauze gets soaked in the water.
• Then start whirling the thermometer so that evaporation takes place.
• After 5 minutes of whirling, note the temperature of the wet bulb and the dry bulb. We got 18 °C on the wet bulb and 25 °C on the dry bulb. These would be wet bulb temperature and dry bulb temperature respectively.
• Now subtract the wet bulb temperature from the dry bulb temperature so that you may get the wet-bulb depression and we got 7 degrees.
• Using the psychrometric chart find the relative humidity with the help of dry bulb temperature and wet bulb depression.
• According to the chart when the temperature of the dry bulb is 25 °C and dry bulb depression is 7° we get relative humidity of about 50 %.

Psychrometer showing wet bulb temperature and dry bulb temperature⇫

Dry Bulb temperature=25 °C

Wet Bulb Temperature=18 °C

Dry bulb depression=Dry bulb temperature-wet bulb temperature

Dry bulb depression=25°C-18°C = 7°C

Now we got dry bulb depression, by comparing this with dry bulb temperature on the psychrometric chart we can get the relative humidity. So,

Psychrometric chart⇩

THE RELATIVE HUMIDITY is 50 %