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* Please note for assignment 4, question 5, you will require making an important correction to the membrane notes: slide 76: \(R = 1 - \displaystyle\frac{C_P}{C_F} \) | * Please note for assignment 4, question 5, you will require making an important correction to the membrane notes: slide 76: \(R = 1 - \displaystyle\frac{C_P}{C_F} \) | ||
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| One hint and one update for [[Assignment 4 - 2012|assignment 4]], question 5: | |||
* The \(A_\text{salt}\) and \(A_\text{solv}\) terms '''''are not''''' the area of the membrane: they are the permeances of the salt and solvent respectively. This unfortunate notation is widely used though in most texts. | |||
* There is a correction, the feed concentration '''should be 2.5 g NaCl per liter''' in the feed ('''not 2.5 wt% NaCl'''). I apologize for wasting your time for those of you that have been iterating with negative concentrations. | |||
* And another hint. I found a way to solve question 5 that leads to faster convergence: | |||
** Specify \(C_F\) and \(\theta\) | |||
** Guess \(C_R\) instead | |||
** Calculate \(C_P\) from equation 5 | |||
** If your calculated value of \(C_P\) is negative or exceeds \(C_F\), then repeat your guess for \(C_R\), until you get a \(C_P\) that lies between 0 and \(C_F\) and double check also that the rejection coefficient from this \(C_P\) is reasonable, around 90 to 99%. | |||
** This approach to estimate \(C_R\) and then \(C_P\) will get you really close to the final answer. | |||
** Now carry on with the rest of the steps in the notes. It's interesting how simply flipping what you guess first leads to much faster convergence. | |||
* And a final hint: this question is much better to solve on a computer, with goal seek, than by hand. There is tremendous sensitivity to initial guesses, so solving by hand will take too long. | |||
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Revision as of 22:22, 2 November 2012
Separation Processes: CHE 4M3
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