Difference between revisions of "Archived-Announcements-2012"

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* '''Important''': parts of assignment 4 will be covered in class on Tuesday. Assignments must be submitted by the start of class on 6 November.
*Some hints and an 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.
:** If you iterate and get a negative value for \(C_P\) or \(C_R\), it simply means that you must decrease your guess for that term, since you obviously can't have a negative concentration.
:* 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.
:* For question 2(B), part 3: by definition, optimization implies we have excess degrees of freedom, i.e. more unknowns than equations. You should get a system of 3 unknowns (including \(A_1\) and \(A_2\)) and 2 equations. Set the 3rd unknown to various values (between its lower and upper bound), and solve for \(A_1\) and \(A_2\). Pick the solution that gives the optimum.
* '''Updated''': Feedback about your [[Course_project_-_2012|course project outline]] has been sent. Feel free to reply with any comments, otherwise, you should have started collecting the information you need to work on your report, such as equations on how to design the separator and capital & operating costs.  
* '''Updated''': Feedback about your [[Course_project_-_2012|course project outline]] has been sent. Feel free to reply with any comments, otherwise, you should have started collecting the information you need to work on your report, such as equations on how to design the separator and capital & operating costs.  
* <span style="color:#AA4444">''Important note''':</span> '''there will be no teaching on Friday (02 Nov), 08:30 to 09:20.''
* <span style="color:#AA4444">''Important note''':</span> '''there will be no teaching on Friday (02 Nov), 08:30 to 09:20.''

Revision as of 18:38, 6 November 2012

From most recent to earliest



  • Important: parts of assignment 4 will be covered in class on Tuesday. Assignments must be submitted by the start of class on 6 November.
  • Some hints and an update for 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.
    • If you iterate and get a negative value for \(C_P\) or \(C_R\), it simply means that you must decrease your guess for that term, since you obviously can't have a negative concentration.
  • 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.
  • For question 2(B), part 3: by definition, optimization implies we have excess degrees of freedom, i.e. more unknowns than equations. You should get a system of 3 unknowns (including \(A_1\) and \(A_2\)) and 2 equations. Set the 3rd unknown to various values (between its lower and upper bound), and solve for \(A_1\) and \(A_2\). Pick the solution that gives the optimum.
  • Updated: Feedback about your course project outline has been sent. Feel free to reply with any comments, otherwise, you should have started collecting the information you need to work on your report, such as equations on how to design the separator and capital & operating costs.
  • Important note: there will be no teaching on Friday (02 Nov), 08:30 to 09:20.
    • I will be at the class though to answer any questions regarding assignment 4.
    • There will be a tutorial-style question (slide 58) that you can ask questions on. This question will be in assignment 5 ... so get a head start.
  • Some changes to deadlines, based on student requests (due to other course loads):
  • The slides from Friday (26 Oct) have been updated - all the solutions are added to the slides. Please ensure you understand how to use the ternary diagram. Hint: there might just be a pop-quiz on Tuesday as part of assignment 5.
  • I am planning to cancel class on Tuesday morning, due to the bad weather. I will rely on the university's choice to cancel class, please check http://mcmaster.ca in the morning before class. Update at 630am: classes are going ahead on Tuesday.
  • For class on Friday (26 October 2012):
    • Make sure you watch and understand this video on ternary phase diagrams: the class is going to rely heavily on that.
    • I recommend you attempt the 5 questions in the course slides prior to class.
    • Bring a ruler, pencil and eraser to class to work with ternary diagrams.
    • Updated notes are available. Print slides 29, 30, 32 and 35 on separate, large pages.
  • Assignment 4 is posted - due later, on 01 November, as there are several midterms in other courses this week.
  • Important correction to the notes: slide 76, please make this correction: \(R = 1 - \displaystyle\frac{C_P}{C_F} \)
  • Read ahead: a highly recommended reading is chapter 8 on liquid-liquid extraction from Seader, Henley and Roper.
  • If you missed class on 18 Oct, please make sure to watch the video recording; Friday's class will not have too much time to recap before moving on. Here are some questions to think about before class:
    • What happens, in terms of osmosis, on a really hot day to fluid flow in a tree?
    • Is \(P_\text{solv}\) going to change if we use a different solute?
    • If we double the pressure drop, will we double the solvent flux?
    • Why did we not take osmotic pressure in account for microfiltration and ultrafiltration?
    • In RO: what will be the expected effect of increasing operating temperature?
  • The midterm solutions have been updated with question 3 included now.
  • Updated details regarding the course project are posted. Please note the deadline of 18 October for the project outline.
  • Thanks everyone again for your constructive feedback about the midterm. Once Daryl and I have graded the midterm I will make a judgement on how to adjust the grades, if required.
  • This anonymous comment was received from the course website:

Kevin,

Friday night's 4M midterm was too hard! More specifically, the 24 mark question was very unfair. It is material that was covered on Thursday - ONE day before the midterm! Its not fair to test us on this and make it worth 24 marks! Normally, our other profs give us at least a week to digest the material before it is covered on a midterm. Other than that, the question itself was tough and many of my colleagues also were confused by it. Basically, if we did not get this question, we automatically drop to 76%, not taking into account other mistakes.

Please - reconsider the marking allocation of this question !

The other thing - the midterm was way too long. I understand that you gave us extra time but 2 hours and 45 minutes is almost 3 hours - which is the duration of a final exam! This is not to be expected for a 15% midterm.

Those are some thoughts - I would appreciate your addressing them!

Thanks.
I appreciate and take any feedback seriously. I'm interested in whether this is one data point (1 student out of 80), or if these issues are of general concern. Feel free to message me via the course website to address the issues of whether question 3 was (a) unfair (b) confusing, (c) too soon; and lastly (d) whether the midterm was too long. I will discuss these in class on Tuesday.
In the mean time, please review the midterm solutions; I will take up question 3 in class on Tuesday. Please redo this question and hand it in at class on Tuesday morning as question 2 of assignment 4. You must do it on your own to maximize your learning. You may hand it in electronically if you cannot make it to class.
A membrane operating with pure feed of water produced a flux of 0.20 \(\text{kg.s}^{−1}\text{.m}^{−2}\); this was with a pressure difference of 20kPa. When operated with a protein-water mixture and a 20 kPa pressure difference, a flux of 0.04 \(\text{kg.s}^{−1}\text{.m}^{−2}\) was measured at steady state. What would be the expected flux for this same protein-water mixture, but at a pressure difference of 30kPa?
  • Clarification in question 1, assignment 3: please ignore the word "needle"; it is simply a rectangular object.
  • Slides for the guest lecture on membranes are now available. This material forms part of the course content.
  • Please note: the solutions to the assignment will be discussed in class on 9 October. Assignments MUST be handed in at the start of class.
  • Course project selection is starting. It is mandatory to fill out this form before noon, 27 September. Also note that topics will generally be allocated on a first-reserved basis.
  • There is a piece of information missing for Assignment 2, Q4: the volumetric flow rate coming in. What I will ask you to do instead, is please present your answer as a plot, showing the minimum particle size that can be removed (y-axis) as a function of the volumetric feed flow rate, Q, in units of ms−1, on the x-axis.
  • A great presentation on beer clarification, showing photos of the internals of the disk-bowl centrifuge. Notice the dimensions are similar to those we designed in class on Friday. As mentioned, here is a 10 page report on centrifuges for beer clarification. Course projects for this course will be similar.
  • The practice question in class is available: see the link to "Practice questions for tests and exams" on the main course page. More questions will be added there as the course progresses, so keep checking that page.
  • Given the clashes with other evening classes and with CSChE, the only feasible midterm date is Friday, 12 October at 18:30.
  • The second assignment is available; due on 25 September (date has changed).
  • Comments, questions, feedback? Don't wait for official course evaluations.
  • The first assignment is out. Due on 14 September. To clarify, in question 1, please state:
    • the box from the table (e.g. gas-gas)
    • the name of the unit (e.g. cryogenic distillation)
    • the input stream (air with mostly nitrogen and less oxygen)
    • the two or more output streams (high purity oxygen; high purity nitrogen; high purity argon; other mixed purity streams).
  • Please use the feedback page to let me know which evening works best for the midterm: 15, 16, 17, 18 or 19 October.
  • Also, if you didn't get a chance to let me know which separation unit ops you are interested in seeing covered in the course, then please let me know.
  • The first class is on Thursday morning, 08:30AM, in MDCL 1110. Please bring
    • the course outline, and
    • any thoughts on what you want to see covered in this elective course.