An absorber is to recover $99\mathrm{.}5\%$ of the ammonia in the air$-$ammonia stream fed to it$,$ using

water as the absorbing liquid. The ammonia content of the air is $16$ mole$\%.$ Absorber

temperature is to be kept at $30\backslash$deg C by cooling coils; the pressure is $1$ atm.

a$.$ What is the minimum water rate?

b$.$ For a water rate $35\%$ greater than the minimum, how many overall gas$-$phase transfer

units are needed.