MT Test #2, 11/22 @ 10:30 in Johnson 075.
Please post any questions you have about Test #2 as comments to this post.
Best of luck on the test !
Best of luck on the test !
posted by Dr. B at 9:08 PM
Sunday, November 19, 2006
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12 Comments:
So did we decide on 4 note sheets for the test?
Jeff:
You can have FOUR 8.5"x11" cheat sheets on the test on Wed and you can write on both sides.
I just posted the 3 diagrams you will need to solve the old exam 2 problems.
Hi Dr.B,some random question:
Do we assume when given or asked for tray efficiency, it's always Eo ?
Thanks,
i'm looking at the slides from oct 23 and not understanding the equations on slide 5 for L' and G' and how they are related to L and V. when i try deriving it based on the definitions, i get L'=L*(1-x). can you explain how you got what you got?
why in the preparation for exam1 said that for Kirkbride: Nstate= Nrs+Nss. However, in the slide said that, Nstate= 1(partial reboiler) +1(partial condenser)+Nrr +Nss + 1 (feed state).
Which are correct?
Since Dr. B has not responded yet, maybe this will help you guys.
anon,
in his review for exam 2, he states that rs includes reboiler and ss includes condenser if there is one.
karen,
go off of the definitions of V' and L" and use a balance with these instead of V and L. pg 202 in the text explains this really well.I believe his equations are wrong but they should never be needed. And G'=V' , last years book used G' I believe.
Pen,
Eo is the over all tray efficiency, I believe he will tell us which efficiency to use and if not just ask during the test because you can not assume anything unless you want to take the chance of being wrong.
karen:
L has units of mole of liquid mixture/h
L' has units of moles of inert or solute-free liquid / h
X = x/(1-x) has units of mole of solute / mole inert liquid
So, you are correct: L' = L (1-x)
L x = L' X
Thank you for pointing out this error in the slide. I just fixed it.
pen and pencil:
I do not think that it is a good idea to assume that a tray efficiency referes to any particular TYPE of efficiency. If you are not sure which type of efficiency is given or asked for, please ASK ME !
Anon 8:02
This feed stage thing is messy.
When you calculate NRS/NSS in Kirkbride, it REALLY means N(above the feed stage) / N(below the feed stage). A partial condense is one of the stages above the feed stage, but it is NOT in the column. The reboiler is one of the stages below the feed stage, but it is not in the column either. You just have to be careful when you are trying to determine how many stage ARE in the column above the feed stage and how many are in the column below the feed stage. I always draw myself a picture as I did in the HW solution so I don't screw up.
I went both way on the feed stage issue, but let's agree now ... we will NOT count the feed stage as a special stage that is neither in the RS nor the SS. It is just the point that divides the RS from the SS. Sorry for the confusion about the feed stage.
Anon 10:07 PM
Nice work ! Thanks for helping out.
I did not reply earlier b/c I just got home at 10 and had to eat dinner. But I am at the switch now...
Your answer to Anon is right on the money.
Your answer to Karen is good. I think my answer will compliment what is in the text on pg 202 well.
Your answer to Pen & Pencil is also correct. I will tell you which efficiency I mean and if there is any doubt ASK !
It looks like you are in very good shape for the test tomorrow !
Best of luck to you.
A reminder about test taking...
1- Find the problem that you are most confident about and do it first
2- Get ALL of the given info out of the problem statement and onto your paper. Cross off EACH WORD in the problem statement as you translate it into given variable, eqns, etc on your paper. Don't stop on the porblem until EVERY WORD has been crossed out.
3- Write all the relevant equations and make a diagram. This very very important to getting partial credit.
4- If you get stuck switch to a different problem and repeat step 2.
DON'T PANIC ... snacks help with this part.
Best of luck and Happy Thanksgiving !
Dr. B
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