3 replies to this topic

[Spliknot13]

I need help on solving this one. So the problem is Dry air is bubbled through 25.0 liters of water at a rate of 15 L(STP)/min. The air leaving the liquid is saturated with water at 25 C and 1.5 atm. How long will it take for all the water to vaporize? Err. So what I did was got the volume/min at 25C and 1.5 atm which is 10.915 L/min. I sort of just subtracted the concentrations of dry air and air saturated with water to get the mole of water/L then multiplied it by 10.915 which is 0.1822 mole water/min. I think 25L water is just approximately equivalent to 25000g/(0.1822x18) which is 127 hours which is wrong. Already thought of using the saturated pressure of water at 25 C but I dont know how to use it. Comments/ideas will be really helpful. By the way it says here in the book that the answer is 67.8 days.

[latexman]

I wish you had attached your calcs.  That would have been faster for us.

 

Absolute saturation (absolute humidity) from Felder and Rousseau's Elementary Principals of Chemical Processes:

 

s_a(h_a)=p_vM_v/[(P-p_v)M_{dry air}]          mass of vapor/mass of dry air

 

p_v=p*(T) at saturation

 

p*(T)=vapor pressure of water

p_v=partial pressure of water

Mv=molecular weight of water

M_{dry air}=molecular weight of dry air

 

I assumed the flow of air was 15 L/min of dry air and got 49 days.  Is air measured before or after the water?

Edited by latexman, 18 June 2013 - 06:51 PM.

[latexman]

Found my error.  67.8 days!  It isn't pretty, but I attached my calcs.

Attached Files

•  3352_001.pdf   87.5KB   161 downloads

Edited by latexman, 18 June 2013 - 10:14 AM.

[Spliknot13]

thanks a lot for the help.