In: Chemistry
1. Wet air containing 60.4 mol% of pure water at 82.5˚C is fed
to a dehumidifier at a rate of 185 mol/hr. Outlet of the
dehumidifier consists of 2 streams – one stream of drier air and
the other stream is pure liquid water. The outlet streams are in
vapor-liquid equilibrium at 812 mmHg and 31.7oC.
a) Draw the process flow diagram, number the streams, and label the
components in each stream.
b) Find the component mole flow rates (mol/hr) exiting the
dehumidifier.
c) If the temperature of the inlet wet air increases by 10oC, will
the molar flow rate of liquid water exiting the dehumidifier
increase, decrease, or stay the same? Justify your answer.
Inlet to the humidifier
Flow rate of wet air = 185 mol/hr, Flow rate of water= 185*0.604=111.74 moles/hr
Moles of dry air = 185-111.74 =73.26 moles/hr
Outlet of humidifier
At 31.7 deg.c, vapor pressure of water =33.6 mm Hg, Total pressure= 812 mm Hg
At Equilibrium, partial pressure of water vapor = vapor pressure of llquid= 33.6 mmHg
Parital pressue of dry air= 812-33.6=778.4 mm Hg
Partial pressure of water vapor/ Partial pressure of dry air= 33.6/778.4= 0.0432
= moles of water vapor/moles of dry air
Mole of water vapor = 0.0432*73.26=3.165 moles/hr, moles of dry air = 73.26 moles/hr
Second stream from de humidifier
Hence molar flow rate of liquid water leaving= moles ofwater entering-( moles of water in air=)111.74- 3.165=108.575 moles/hr
C) when temperature of inlet wet air is increased and outlet conditinos remains the same at 31.7 deg.c and 812mm Hg, there will not be any change in molar flow rate of liqud water exiting the dehumidifier. Since moles of water vapor are calculated based on moles of dry air.