# Top-rated ScreenCasts

Text Section | Link to original post | Rating (out of 100) | Number of votes | Copy of rated post |
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06.2 Derivative Relations | Click here. | 36 | 5 |
Heat Capacity Volume Dependence (uakron.edu, 10min) This example derives how the heat capacity of the gas depends on volume, ie. (∂ Comprehension Questions: 1. The van der Waals (vdW) equation of state (EOS) is: |

03.6 - Energy Balance for Reacting Systems | Click here. | 35 | 4 |
You can turn Excel into a crude process simulator (e.g. ASPEN, ChemCAD, ProSim, HYSYS, ...) by implementing an xls feature that is often overlooked. (7min, uakron.edu) You need to enable the iteration feature and then you simply need an initial guess about the masses of any recycle streams. This presentation illustrates the mass balance calculation for the dimethyl ether process (2CH3OH = CH3OCH3 + H2O). A subsequent video (below) shows how to add stream enthalpy calculations using the path of Figure 2.6c and Eqn 3.5. Then you can easily perform the energy balances. One important feature of having the energy balance is to facilitate performing an adiabatic reactor calculation, also illustrated below. You should also be mindful of tear stream control to ensure that your iterations do not diverge. Comprehension questions: |

09.09 - Calculation of Fugacity (Solids) | Click here. | 33.3333 | 6 |
The fugacity of a solid (uakron, 19min) follows a similar trend to that of a liquid, but there can be unexpected implications. The impact of pressure requires careful consideration. NIST Webbook lists the melting temperature of xenon as 161.45K and the Antoine equation as log Cp=22.7 J/mol-K, ^{V}Cp=44.4 J/mol-K, ^{L}ρ=2.9662 g/cm3. Wikipedia lists the solid density as 3.540 g/cm3 (and the liquid density as 3.084) and the heat of fusion as 2270 J/mol. You may assume ^{L}Cp=^{L}Cp. Use Eq. 7.06 to describe the vapor phase. You may assume ω = 0 for the purpose of these calculations. This screencast shows a ^{S}sample calculation to solve for: (a) the vapor fugacity at 162 K and 0.085 MPa (b) the liquid fugacity in equilibrium with the same vapor at 162 K and 0.085 MPa (c) the liquid fugacity at 162 K and 8.5 MPa (d) the solid fugacity at 161.45 K and 0.082 MPa (e) the solid fugacity at 162 K and 8.5 MPa. If you are still having trouble understanding the ways that all these fugacities relate, you might like to view the phase diagram implications of VLSE (uakron, 9min). Comprehension Questions: 1. How much did raising the pressure to 8.5 MPa change the liquid fugacity (bars)? T and H at the triple point._{fus} |

08.01 - The Departure Function Pathway | Click here. | 32 | 5 |
Demystifying The Departure Function (11min) (uakron.edu) Comprehension Questions: 1. In the diagram of ( 3. Identify the steps in #2 above as departure function or ideal gas contributions. 4. For propane at 355K and 3MPa, ( U-U)= -2572 J/mol. We can compute ^{ig}U(355K)-^{ig}U(230K)=8000 J/mol. The departure function for liquid propane at 230K, 0.1MPa is (^{ig}U-U)= -16970 J/mol. Compute the value of "^{ig}U" at 355K and 3MPa relative to liquid propane at 230, and 0.1MPa using this information. 5. Compare your answer to the value given by PREOS.xlsx. 6. Compare your answer to the value given by the pathway of Figure 2.6c. (Hint: use Eqn. 2.47 to decide whether 355K,3MPa corresponds to a vapor or liquid.) |

10.02 - Vapor-Liquid Equilibrium (VLE) Calculations | Click here. | 32 | 5 |
Use VLookup and shortcut estimates of Antoine coefficients (see above) to quickly generate the Pxy phase diagram for an ideal solution. (11min, uakron.edu) This video shows a Note: This is a companion file in a series. You may wish to choose your own order for viewing them. For example, you should implement the first three videos before implementing this one. Also, you might like to see how to quickly visualize the Txy analog of the Pxy phase diagram. If you see a phase diagram like the ones in section 11.8, you might want to learn about LLE phase diagrams. The links on the software tutorial present a summary of the techniques to be implemented throughout Unit3 in a quick access format that is more compact than what is presented elsewhere. Some students may find it helpful to refer to this compact list when they find themselves "not being able to find the forest because of all the trees." Comprehension Questions: 1. Create a Pxy diagram for methanol+benzene at 90C based on the ideal solution SCVP model. Be sure to include all appropriate labels and label your sketch as quantitatively as possible. Compare your model to the data in HW 11.10 by including those points in the plot. Explain similarities and discrepancies. |

12.05 - MOSCED and SSCED Theory | Click here. | 30 | 6 |
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: |

08.03 - The Entropy Departure Function | Click here. | 28 | 5 |
The Entropy Departure Function (11:22) (uakron.edu) T,V) to S(^{ig}T,P). (2) When all is said and done, combining S with U (derived in 08.02) gives A (=U-TS) and A gives G (=A+PV), implying that other departure functions can be obtained by simple arithmetic applied to U and S.Comprehension Questions: The RK EOS can be written as: _{TV}/R of the RK EOS.2. Use Eqn. 8.27 to solve for ( A-A)^{ig}_{TV}/RT of the RK EOS.3. Use Eqns. 8.22 and 8.27 to solve for ( S-S)^{ig}_{TV}/R of the RK EOS. |

08.07 - Implementation of Departure Functions | Click here. | 28 | 5 |
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. |

03.5 Mixture Properties for Ideal Solutions | Click here. | 25 | 4 |
Stream enthalpies for the DME process (uakron, 7min) can be estimated using the "heat of reaction" pathway (Fig 3.5a) or the "heat of formation" pathway (Fig 3.5b). This presentation is based on Fig 3.5b, which is very similar to Fig 2.6c. The main difference is the inclusion of the heat of formation for each compound relative to its elements. Including the heat of formation puts the reference state for each compound on the same basis of comparison (ie. the elements). If one stream (e.g. "products") possesses more enthalpy than another stream (e.g. "reactants") then the energy difference between the streams (e.g. "heat of reaction") would be accounted for by simply subtracting the two stream enthalpies. Reactions inherently involve multiple components, so including the heats of formation in the stream enthalpies, as well as the other enthalpic contributions represented in Fig 2.6c, is inevitable. These sample calculations are illustrated for all the streams appearing in the DME process. The presentation follows up on the discussion of Fig 2.6c for pure fluids. Once you understand the calculations for each pure fluid, the mixture property simply involves taking the molar average, so: Hf+_{i}CpΔ_{i}^{ig}T+(q-1)*_{i}H). In this equation, (_{i}^{vap}q-1)*_{i}Haccounts crudely for departures from ideal gas behavior. For example, if a stream is a vapor, then _{i}^{vap }q=1 and Hdoesn't matter. If ^{vap }q=0, then the stream is a liquid and Hmust be subtracted. We will study more accurate models of ideal gas departures in Unit II.^{vap }Comprehension Questions: 1. Compute the enthalpy, H(J/mol), of methanol at 250C and 2 bars relative to its ideal gas standard state elements. 2. Compute the enthalpy, H(J/mol), of DME at 250C and 2 bars relative to its ideal gas standard state elements. 3. Compute the enthalpy, H(J/mol), of water at 250C and 2 bars relative to its ideal gas standard state elements. 4. Compute the enthalpy, H(J/mol), of a stream that is 50% methanol, 25% DME, and 25% water at 250C and 2 bars relative to its ideal gas standard state elements. |

12.05 - MOSCED and SSCED Theory | Click here. | 24 | 5 |
This video walks you through the process of transforming the Scatchard-Hildebrand model into the SSCED model using Excel (6min, uakron.edu) It steps systematically through the modifications to the spreadsheet to obtain the new model. You should implement the Scatchard-Hildebrand model before implementing this procedure. Comprehension Questions: z = 0.20 (c) 370K and _{m}z = 0.70._{m}3. Compare your predicted Txy diagram to the predictions by the MAB and Scatchard-Hildebrand models. Describe the differences briefly for each case. 4. Search for experimental data on the system ethanol+toluene. Modify your spreadsheets to plot the experimental data (points) on the same plot with the predictions. Which model provides the most accurate predictions when compared to data? 5. Suppose you set k12=0 in the SSCED model. Does that improve the comparison to experimental data? Other models? Does the combination of k12=0 and k12=k12(alpha,beta) bracket the range of values that fit reasonably? |