Learning undergraduate engineering thermodynamics might be less painful with a blog. I hope that students, faculty and interested observers will share their thoughts on the laws of thermodynamics, phase and chemical equilibrium and many related topics.
My TI-83 is programmed to calculate A, B, and all the residual thermodynamic properties plus the actual/ideal specific volumes and graph the cubic Z for a pure substance. Will we have to calculate these values for mixtures as well on the test?
To save time on the test will it be acceptable/will we get full credit if we use symbols where possible instead of words e.g. the simplifications for the Clausius-Clapeyron equation represented as the following:
ahayles 2:37 PM I like symbols, but they don't go very far without some words explaining what you are doing and why. If I get confused by your work, you lose points. I do not think you will find this test to be time-limited, so play it safe and go with BOTH words and symbols this time.
Should we write the equations out for the residual properties, A, B, and Z etc. or will simply putting down our calculator output be acceptable? Thanks!
ahayles 2:57 PM GOOD question. The output from your calculator is NOT adequate ! You must write out the equations with numbers and units plugged in properly and THEN tell me what you got for Z. That is the only way you will get full credit. Best of luck on Tue !
OK I have my calculator programmed to calculate the cubic Z, A, B and all residuals for a binary mixture now. Will we have to calculate these values for a mixture with N>2 components?
ahayles 9:38: It is very unlikely that you will use SRK with more than 2 components on this test. If you can do 2, I think you could do more (given enough time).
ahayles 9:38pm I am a bit unsure as to how you calculated the residuals for a binary mixture. For S, H, and U the residual is based on m, which we don't have mixing rules for. Did you have a different residual for each species? That also brings up the question of whether we can have A or G residuals for mixes which are only based on A, B, and Z or whether they are individual to the species?
danny 9:35 PM I cannot find my favorite book on this subject, but I think I know the answer here.
You calculate Ur, Hr and Sr for each component in the mixture using the m value for each component. Then, the residual property for the mixture is just the sum{molefrac*residual} for all species.
If this issue comes up on the test tomorrow, this is what I suggest you do.
14 comments:
My TI-83 is programmed to calculate A, B, and all the residual thermodynamic properties plus the actual/ideal specific volumes and graph the cubic Z for a pure substance. Will we have to calculate these values for mixtures as well on the test?
To save time on the test will it be acceptable/will we get full credit if we use symbols where possible instead of words e.g. the simplifications for the Clausius-Clapeyron equation represented as the following:
-Vwiggle(liq) << Vwiggle(vap)
-delta(Z) = 1
ahayles 11:55 PM
Using SRK to calculate the residual properties of mixtures is fair game for the test on Tuesday.
ahayles 2:37 PM
I like symbols, but they don't go very far without some words explaining what you are doing and why. If I get confused by your work, you lose points. I do not think you will find this test to be time-limited, so play it safe and go with BOTH words and symbols this time.
Should we write the equations out for the residual properties, A, B, and Z etc. or will simply putting down our calculator output be acceptable? Thanks!
ahayles 2:57 PM
GOOD question.
The output from your calculator is NOT adequate !
You must write out the equations with numbers and units plugged in properly and THEN tell me what you got for Z.
That is the only way you will get full credit.
Best of luck on Tue !
Will we be using lee-kesler, virial eos, wagner equation? Or are we focused on SRK or RK only?
OK I have my calculator programmed to calculate the cubic Z, A, B and all residuals for a binary mixture now. Will we have to calculate these values for a mixture with N>2 components?
OK I know you touched on this in class and you want to leave some mystery as to what exactly will be put on the exam but I have to ask:
Will we have to calculate the cubic Z and residual values for a mixture of N>3 components?
Eiken 5:16 PM:
No. You do not need to study lee-kesler, virial eos wagneror RK equations of state. Just SRK.
ahayles 9:38:
It is very unlikely that you will use SRK with more than 2 components on this test. If you can do 2, I think you could do more (given enough time).
ahayles 4:31 PM:
No. N<3 on this test. Please study some of the other topics now :)
ahayles 9:38pm
I am a bit unsure as to how you calculated the residuals for a binary mixture. For S, H, and U the residual is based on m, which we don't have mixing rules for. Did you have a different residual for each species? That also brings up the question of whether we can have A or G residuals for mixes which are only based on A, B, and Z or whether they are individual to the species?
danny 9:35 PM
I cannot find my favorite book on this subject, but I think I know the answer here.
You calculate Ur, Hr and Sr for each component in the mixture using the m value for each component. Then, the residual property for the mixture is just the sum{molefrac*residual} for all species.
If this issue comes up on the test tomorrow, this is what I suggest you do.
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