[tuong]

hey guys, I'm having a little trouble over this problem, this is my 1st class in ChE and I'm trying to get a feel for this major



Here's what I have so far:

basis : 30000 lb/hr of sea water with 3.5 wt-% NaCl
final product: 0.01593 mole fraction NaCl
Same quantity of water is boiled off in each effect

My plan for this problem is first I have to find the mass of NaCl in the solution fed, then separate the mass of H2O and NaCl

Next I will divide the mass of the H2O by 3 to determine the amount of H2O that is leaving in each effect

And the evaporation rate will be the same for each effect, thus it represents the mass of H2O leaving one of the effect.

I'm guessing that the wt-% of NaCl will be higher leaving the second effect (after subtracting some mass of H2O after 1st and 2nd effect, the wt-% of NaCl will be its original mass fed divided by the lowered H2O mass)

This is when the problem got me. I don't understand the 0.01593 mole fraction of NaCl in the composition of the solution that is leaving the third effect. Does that number represents the arrow pointing to the right? if so why is it so low? isn't the mole fraction of NaCl be higher since its concentration is getting higer and higer after each effect? And how is it relevant to the problem? was it extra information? Thanks for any help

[ARGOS++]

Dear tuong;

The mole fraction of 0.01593 is not a low number and not to low at all, because for me it corresponds with 5.00%w/w Salt, and so it will be very relevant.

Maybe you have to go for the definition of “Mole Fraction” on Wiki.
(Don’t miss the term normalisation!)

Good Luck!
                    ARGOS⁺⁺