A triple-effect evaporator is to be used to produce a 50 percent NaOH solution from a feed containing 25 percent NaOH. Steam is available at 320°F, and the vapor from the last stage is condensed at 120°F. Backward feed is used. 

(a) If equal amounts of water are removed in each effect, what will be the concentrations in the intermediate effects, the boiling-point elevation in each effect, and the net temperature differences available for heat transfer? 

(b) With the same terminal temperatures and more than three effects, what is the maximum number of effects that could be used?