In the December 2nd blog, I talk about solving the algebraic equations in early chapters of the book using Comsol Multiphysics rather than just Excel, MATLAB, and AspenPlus. I’ve added some examples – another case of two simultaneous equations from Eq. 4.16 and a new one representing vapor-liquid equilibrium, Eq. (3.9), page 32, and the problem in Figure 2.1, page 14. Next up: Chapters 5 and 6.
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Chemecomp's Blog 
hi~i have some problems while doing the exercise 5.7~ may i know how to determine the water needed initially and how to maintain the amount of purged inert gas so that the ratio can keep constant at 0.04? thanks a lot~^_^
If you are solving it using Excel, you use Solver. This is an add-in, so be sure it has been added. See page 75 of the book for an example involving a chemical reaction equilibrium. Suppose you want cell E35 to be 0.04. The you can define a cell E36 = E35-0.04. Then open Solver and say you want cell E36 to be zero and adjust cell E34 to make that happen. Set up your spreadsheet so that cell E34 is the purge ratio. Then solver adjusts cell E34 until cell E36 is zero. Of course the cell numbers are arbitrary. See also p. 292 in the appendix about Solver. If you go to the web site, ChemEComp.com, the “Complicated process solved with Excel” is a problem from the 1st edition (not in the 2nd edition) that uses Solver, and it explains the same thing.
If you are using Aspen, you use the Design Specification Block which is described on page. 102.
Hope this helps.
Bruce