A packed tower is used to absorb ammonia from air using aqueous sulfuric acid. The vapor enters the tower at $31lbmolf{t}^{-2}{h}^{-1}$ and contains $1$mol$\%$ ammonia. An aqueous solution of sulfuric between ammonia and sulfuric acid, the equilibrium partial pressure of ammonia above the solution can be taken as zero. We desire an outlet ammonia concentration of $0\mathrm{.}01$mol$\%$ in the vapor stream.

a$)$ Calculate the number of transfer units $($based on a vapor side driving force$)$ for this system.

b$)$ How do the vapor and liquid fluxes affect mass transfer in this particular system?