Top-rated ScreenCasts

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03.6 - Energy Balance for Reacting Systems Click here. 20 1

In case you need a little extra help on energy balances after iterating mass balances, this video walks you through the process. (8min, uakron.edu) for the same process flow diagram related to dimethyl ether synthesis.

Comprehension Questions:

1. Choose any process flow diagram from your material and energy balances (MEB) textbook that has a recycle stream. Solve the problem using this technique and compare to the answer you obtained in MEB class. Estimate stream enthalpies for every stream and compute the overall energy balance of all product streams to all feed streams. Does the process require net heat addition or removal?
2. Suggest limitations of this approach. What are the assumptions? Which assumptions seem most suspect?

05.2 - The Rankine cycle Click here. 20 1

Rankine Example Using Steam.xls (uakron.edu, 15min) High pressure steam (254C,4.2MPa, Saturated vapor) is being considered for application in a Rankine cycle dropping the pressure to 0.1MPa; compute the Rankine efficiency. This demonstration applies the Steam.xls spreadsheet to get as many properties as possible.

Comprehension Questions:

1. Why does the proposed process turn out to be impractical?

2. What would you need to change in the process to make it work? Assume the high and low temperature limits are the same. Be quantitative.

3. What would be the thermal efficiency of your modified process?

12.05 - MOSCED and SSCED Theory Click here. 20 1

There are so many activity models, how can you keep them straight? This video shows how MAB, SSCED, and Scatchard-Hildebrand models are all closely related.(9min,uakron.edu) By changing the assumptions, one model can be transformed into the other. So focus on remembering one model very well, then remember the small adjustments to obtain the other models.

Comprehension Questions:
1. Suppose we are trying to find the solvent most compatible with dilute ethanol. Which of the following is most compatible according to the MAB model?  (a) water (b) benzene (c) n-octanol.
2. Suppose we are trying to find the solvent most compatible with dilute ethanol. Which of the following is most compatible according to the ScHil model?  (a) water (b) benzene (c) n-octanol.
3. Suppose we are trying to find the solvent most compatible with dilute ethanol. Which of the following is most compatible according to the SSCED model?  (a) water (b) benzene (c) n-octanol. (Hint: consider the infinite dilution activity coefficient.)

11.05 - Modified Raoult's Law and Excess Gibbs Energy Click here. 20 1

Extending the M1 derivation of the activity coefficient to multicomponent mixtures  (uakron.edu, 14min) is straightforward but requires careful attention to the meaning of the subscripts and notation. It is a good warmup for derivations of more sophisticated activity models. This presentation begins with a brief review of the M1 model and its relation to the Gibbs excess function, then systematically explains the notation as it extends from the binary case to multiple components.

Comprehension Questions
1. Derive the activity coefficient for the multicomponent M2 model.
2. Derive the activity coefficient for the multicomponent Redlich-Kister model.

08.07 - Implementation of Departure Functions Click here. 20 2

Helmholtz Energy - Mother of All Departure Functions. (uakron.edu, 10min) This screencast begins with a brief perspective on energy and free energy as they relate to concepts from Chapter 1 and through to the end of the course. Then it focuses on how the Helmholtz departure function is one of the most powerful due to the relations that can be developed from it. The Helmholtz departure is relatively easy to develop from a density integral of the compressibility factor. Then the internal energy departure can be derived from a temperature derivative. Alternatively, if the internal energy departure is given, the Helmholtz energy can be inferred by integration, and the compressibility factor can be derived from a density derivative. 
Comprehension Questions: (Hint: some of the following may be answered in later videos below.)
1. Write an equation that takes you from the Helmholtz energy departure function to Z.
2. Write an equation that takes you from the Helmholtz energy departure function to (U-Uig)/RT.
3. Derive the internal energy departure function for the vdW EOS using Eqn. 8.22.
4. Derive the Helmholtz energy departure function for the vdW EOS using Eqn. 8.25.
5. Use the result of #4 to derive the internal energy departure function for the vdW EOS.

07.06 Solving The Cubic EOS for Z Click here. 20 2

Using a macro to create an isotherm (Excel) (msu.edu, 14:31) The tabular Excel display is convenient for viewing all the intermediate values, but no so good for building a table such as for an isotherm. This screencast shows how to write/edit a macro to build a table by copying/pasting values. The screencast creates an isotherm on a Z vs. Pr plot over 0.01 < Pr < 10.

08.07 - Implementation of Departure Functions Click here. 20 1

Helmholtz Example - vdW EOS (uakron.edu, 18min) This video begins with a brief review of the connection of the Helmholtz departure with all other departures then shows four sample derivations assuming that Z is given by the vdW EOS: (1) the Helmholtz departure , (2) the internal energy departure from the Helmholtz departure. (3) the Helmholtz energy from the internal energy (4) the Z factor from the Helmholtz departure. The procedures illustrated here can be applied to any EOS starting with any part (U, A, or Z) as given to derive any other departure: ZUHAGS.
Comprehension Questions: The virial EOS for SW fluids can be written as: Z = 1 + Bρ/RT where B = 4b+[4b(λ^3-1)] [exp(βε)-1], b = πNAσ^3/6.
1. Derive an expression for the Helmholtz departure.
2. Use the result of #1 to derive the internal energy departure.
3. Use the result of #2 to derive the Helmholtz departure. What is the integration constant in this case?

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