2. A single-effect forced-circulation evaporator is to be used to evaporate 50,000 lb/hr of 50% NaOH solution to 70% NaOH. The pressure at the vapor space is 3 in. Hg absolute. Saturated steam at 70 psig is to be used as the heating medium. It is estimated that an overall coefficient of 700 BTU/lu-ft--F will be obtained. Determine the heat-transfer surface required and the steam economy if the feed to the evaporator is at 200F