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A triple-effect evaporator is to be used to evaporate 20,000 lb/hr of 10% NaNO3 solution to obtain a 50% NaNO3 product. The system is arranged for forward feed, which enters at 70F. The steam suppled to the first effect is saturated at 50 psig, and the pressure at the vapor space of the last effect is 4 in. Hg absolute. The heat-exchange areas of all these effects are equal. The following additional information may be helpful: Overall coefficients for the tree effects are 550, 500 and 400 BTU/hr-ft2-0F, respectively Specific heats of NaNO3 solution can be expressed by the equation Cp = 4.175 - 3.742x + 2.166x7, where x= weight fraction NaNO3 and Cp = specific heat in Joules/g.C at 20C and 1 atm pressure. Determine a. Steam economy b. Temperature in each effect Heating surface required in each effect