Thus, there is not just one -value that you can use in the calculations. įor most of these options, the activity coefficient depends upon the liquid mole fractions, and that means the A -values depend upon the liquid mole fractions, too. This ensures that the formula is correct for all components. Step 4 You can also check one term in the Rachford-Rice equation using detailed calculations, and then copy the equation down. Step 2 You need the Rachford-Rice equation to sum to zero, which is evident in the spreadsheet. (3.8) and (3.1), and these are included in columns G and H. Once you find the fraction vapor, the mole fractions in the two phases are easy to calculate using Eqs. Step 3 You can then use Goal Seek to make the Rachford-Rice equation (cell F9) zero by changing the fraction of the feed that is vapor (cell DI), giving the result shown. Once the value of f is known, you can calculate the value of the liquid compositions, x, and vapor compositions, y, using Eqs. Thus, you can apply here the same methods used with Excel and MATLAB in Chapter 2. Notice that, if the A -values and inlet compositions Zi are known, this is a nonlinear equation to solve for u. This is called the Rachford-Rice equation.
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