Question

Air at 45^O​C (dry bulb) and 10% relative humidity is to be humidified adiabatically to 70% relative humidity.

(a) Use the psychrometric chart to estimate the adiabatic saturation temperature of the air.

(b) Estimate the final temperature of the air and the rate at which water must be added to humidify 15 kg/min of the entering air.

(c) What have you assumed in carrying out this calculation?

Answer 1

a) From the psycometric chart, the adiabatic saturation temperature for air at Dry bulb = 45C and 10% Relative humidity(RH) is Twet bulb =Twb= 21 C

Absolute humidity under these condition = 0.006 Kg H2O/Kg dry air

b) The absolute humidity of exit gas determined from the chart under the following conditions:

Twb = 21 C and RH = 70%

i.e the intersection of the Twb and RH curve leading to the absolute humidity value = 0.014 Kg HO/Kg dry air

Find flow rate of inlet Dry air = 15 /1.0026 = 14.96 kg dry air/min

Amount of water that must be evaporated = 14.96 (0.014-0.006) = 0.119 Kg H2O/min