An evaporator operating at atmospheric pressure is designed to concentrate 10,000 lb/h of a 10% w/w NaOH solution at 60°F into a 35% w/w solution. Before entering the evaporator, the weak caustic solution is preheated in a heat exchanger by the exit strong caustic which then leaves the exchanger at 90°F. The stream pressure inside the steam chest is 30psig. Assuming that only water vapour is evaporated, calculate the pounds of steam required per hour. State any assumptions clearly. Data: Normal boiling point of 35% w/w NaOH solution = 251°F Specific heat of 10% w/w NaOH solution (assume constant) = 0.9 Btu/lb °F Specific heat of 35% w/w NaOH solution (assume constant) = 0.84 Btu/lb °F Standard heats of solution (1 atm, 77°F) of solutions of NaOH and H₂O: Composition (ratio by -AH° soln (kcal/g-mole NaOH) moles) NaOH 3 H2O 6.90 NaOH 4 H2O 8.23 NaOH 5 H2O 9.02 NaOH 10 H₂O 10.16 NaOH 20 H₂O 10.24 NaOH 30 H₂O 10.21 Ans: 8930 lb/h steam