A double effect evaporator is to be employed in concentrating 15% solution of NaOH at 700F to 40%. The condensing temperature of the vapor in the second effect is 1000F and the saturated steam is available at 3000F. The U values in the first and second effects are 250 and 350 BTU/h-ft2-0F respectively for backward feed and 300 and 200 BTU/h-ft2-0F respectively for forward feed. Assuming a feed of 1000lb/h, determine the overall steam economy in both cases.