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Heat and Mass Transfer

A triple-effect forced-circulation evaporator is to be fed with 20,000 Ib/h of 30% NaOH solution at a temperature 90F. The concentrated liquor is to be 60% NaOH solution. Saturated steam at 20.7Ibf /in² gauge is to be used, and the condensing temperature of vapor from the third effect is to be 100F. The feed order is II,III,I. Radiation and undercooling of condensate may be neglected. Estimated overall coefficients (BTU/ft²-h-F) corrected for boiling-point elevation are given below. Calculate (a) the heating surface required in each effect, assuming equal surfaces in each, (b) the steam consumption, (c) the steam economy.

Effect	Overall Coefficient
I	700
II	1000
III	800

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