A feed containing 2 wt % dissolved organic solids in water is fed to a double-effect evaporator with reverse feed. The f

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A feed containing 2 wt % dissolved organic solids in water is
fed to a double-effect evaporator with reverse feed. The feed
enters at 100ºF and is concentrated to 25% solids. The
boiling-point rise can be considered negligible, as can the heat of
solution. Each evaporator has a 1000-ft2 surface area, and the
heat-transfer coefficients are U1 = 500 and U2 = 700 btu/h.ft2 .ºF.
The feed enters evaporator number 2 and steam at 100 psia is fed to
number 1. The pressure in the vapor space of evaporator number 2 is
0.98 psia. Assume that the heat capacity of all liquid solutions is
that of liquid water. Calculate the feed rate F and the product
rate L1 of a solution containing 25% solids. (Hint: Assume a feed
rate of, say, F = 1000 lbm/h and a value of T1. Calculate the area
and T1. Then calculate the actual feed rate by multiplying 1000 by
1000/calculated area.)