Question

Saturated steam at 25 psia is added to air flowing at the rate of 2000 lb/min. The air is initially at 55F with a 35F dew point. No heat is added or taken from the air. The air leaves saturated. 1) What is the relative humidity of the incoming air.

Answer 1

709%

Step-by-step explanation:

The relative humidity (Rh) of the incoming air can be expressed as a ratio of Actual Vapor Pressure to the Saturated Vapor Pressure expressed as a percentage.

That is Rh = VP/S V P x 100

Convert the air temperature and dew point temperature to Celsius

Air temperature = 55 F while the dew point temperature is 35 F

The formula is 5/9 (T F-32)

T F is Temperature in Fahrenheit

5/9 (55 - 32) = 12.8°C (air temperature in Celsius)

T d is dew point temperature

T d = 35 F

Convert it to Celsius

5/9 (T d - 32)

5/9 (35 - 32) = 1.7°C (dew point temperature in Celsius)

Calculate the Actual Vapor Pressure as follow:

6.11 x 10.0 (7.5 x 12.8/237.7 + 12.8) = 23.4

Calculate the Saturated Vapor Pressure as follow:

6.11 x 10.0 (7.5 x 1.7/237.7 + 1.7) = 3.3

The Relative Humidity (Rh) = Actual Vapor Pressure/Saturated Vapor Pressure x 100

23.4/3.3 x 100 = 709%