8.4-7. Effect of Feed Temperature on Evaporating an NaOH Solution. A single-effect evaporator is concentrating a feed of 9072kg/h of a 10wt% solution of NaOH in water to a product of 50% solids. The pressure of the saturated steam used is 42kPa (gage) and the pressure in the vapor space of the evaporator is 20kPa (abs). The overall heat-transfer coefficient is 1988W/m2K. Calculate the steam used, the steam economy in kg vaporized/ kg steam, and the area for the following feed conditions. (a) Feed temperature of 288.8K(15.6C). (b) Feed temperature of 322.1K(48.9C). Ans. (a) S=8959kg/h of steam, A=295.4m2