A solution containing 25% by weight of NaOH is concentrated to 50% using a triple-acting evaporator system. The heating steam used is at a temperature of 433 K and the steam taken from the final effect condenses at 322 K. The system is fed in opposite directions.

a) Assuming an equal amount of water evaporation in each effect, calculate the boiling point elevations in each effect, the net temperature difference required for heat transfer, and the weight percentages of NaOH reached in the effects.

b) If it is desired to use more than three effects by working at the same temperature values, what is the maximum number of effects that can be used in the evaporator system?