Air at 25C and 1 atm with a relative humidity of25% is to

Chapter 6, Problem 6.98

(choose chapter or problem)

Air at 25C and 1 atm with a relative humidity of25% is to be dehumidified in an adsorption column packed with silica gel. The equilibrium adsorptivity of water on silica gel is given by the expression14 X*(kg water/lOO kg silica gel) = 12.5 p~,o PH,O where PH,O is the partial pressure of water in the gas contacting the silica gel and P~20 is the vapor pressure of water at the system temperature. Air is fed to the column at a rate of 1.50 Umin until the silica gel is saturated (i.e., until it reaches equilibrium with the feed air), at which point the flow is stopped and the silica gel replaced. (a) Calculate the minimum amount ofsilica gel needed in the column if replacement is to take place no more frequently than every two hours. State any assumptions you make. (b) Briefly describe this process in terms that a high school student would have no trouble understanding. (What is the process designed to do, what happens within the column, and why is replacement of the column packing necessary?)