Using a psychrometric chart in the Modern Refrigeration, what will the wet bulb be if the dry bulb is 80 degrees and the humidity is 30%?

Using a psychrometric chart in the Modern Refrigeration, what will the wet bulb be if the dry bulb is 80 degrees and the humidity is 30%?

• A. 58 °F
• B. 60 °F
• C. 62 °F
• D. 64 °F

Answer: (B)

Wet-bulb temperature is the temperature air would reach if it were cooled by evaporation until it becomes saturated. On a psychrometric chart you start from the given dry-bulb temperature and humidity, then imagine evaporative cooling driving the air parcel along an adiabatic path toward the saturated curve. The point where that cooling path hits 100% relative humidity is the wet-bulb temperature. With a dry-bulb of 80 °F and 30% relative humidity, evaporative cooling brings the air down to about 60 °F before it becomes saturated. So the wet-bulb is approximately 60 °F—lower than the 80 °F dry-bulb, but higher than the dew point (which is in the mid-50s for this state).

Wet-bulb temperature is the temperature air would reach if it were cooled by evaporation until it becomes saturated. On a psychrometric chart you start from the given dry-bulb temperature and humidity, then imagine evaporative cooling driving the air parcel along an adiabatic path toward the saturated curve. The point where that cooling path hits 100% relative humidity is the wet-bulb temperature.

With a dry-bulb of 80 °F and 30% relative humidity, evaporative cooling brings the air down to about 60 °F before it becomes saturated. So the wet-bulb is approximately 60 °F—lower than the 80 °F dry-bulb, but higher than the dew point (which is in the mid-50s for this state).