A packed tower is used to absorb ammonia from air using aqueous sulfuric acid. The vapor

enters the tower at $31$ lbmol ft $-2$ h$-1$ and contains $1$ mol$\%$ ammonia. An aqueous solution of sulfuric

acid is used to absorb the ammonia; it is fed at a rate of $24$ lbmol ft $-2$ h$-1.$ Due to the reaction

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?