Top-rated ScreenCasts

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05.4 - Refrigeration Click here. 100 2

Refrigeration Cycle Introduction (LearnChemE.com, 3min) explains each step in an ordinary vapor compression (OVC) refrigeration cycle and the energy balance for the step. You might also enjoy the more classical introduction (USAF, 11min) representing your tax dollars at work. The musical introduction is quite impressive and several common misconceptions are addressed near the end of the video.
Comprehension Questions: Assume zero subcooling and superheating in the condenser and evaporator.
1. An OVC operates with 43 C in the condenser and -33 C in the evaporator. Why is the condenser temperature higher than than the evaporator temperature? Shouldn't it be the other way around? Explain.
2. An OVC operates with 43 C in the condenser and -33 C in the evaporator. The operating fluid is R134a. Estimate the pressures in the condenser and evaporator using the table in Appendix E-12.
3. An OVC operates with 43 C in the condenser and -33 C in the evaporator. The operating fluid is R134a. Estimate the pressures in the condenser and evaporator using the chart in Appendix E-12.
4. An OVC operates with 43 C in the condenser and -33 C in the evaporator. The operating fluid is R134a. Estimate the pressures in the condenser and evaporator using Eqn 2.47.
5. An OVC operates with 43 C in the condenser and -33 C in the evaporator. Assume the compressor of the OVC cycle is adiabatic and reversible. What two variables (P,V,T,U,H,S) determine the state at the outlet of the compressor?

17.07 - Temperature Dependence of Ka Click here. 100 2

You can customize Kcalc.xlsx (uakron.edu, 17min) to facilitate whatever calculations you may need to perform. This presentation shows how to implement VLOOKUP to automatically load the relevant Hf, Gf, and Cp values. It also shows how to automatically use the Cp/R value when a,b,c,d values for Cp are not available. Finally, it shows how a fairly general table of inlet flows, temperatures, and pressures can be used to set up the equilibrium conversion calculation. The initial set up is demonstrated for the dimethyl ether process, then revised to initiate solution of Example 17.9 for ammonia synthesis.

Comprehension Questions:

1. The video shows how the shortcut Van't Hof equation can be written as lnKa=A+B/T. What are the values of A and B for the dimethyl ether process when a reference temperature of 633K is used?
2. The video shows how the shortcut Van't Hof equation can be written as lnKa=A+B/T. What are the values of A and B for the ammonia synthesis process when a reference temperature of 600K is used?

08.02 - The Internal Energy Departure Function Click here. 100 1

Departure Function Derivation Principles (8:03) (msu.edu)
This screencast covers sections 8.2 - 8.8. Concepts of using the equation of state to evaluate departure functions. The screencasts also discusses the choice of density integrals or pressure integrals. The use of a reference state is discussed.

11.02 - Calculations with Activity Coefficients Click here. 96 5

Dew Temperature (7:57) (msu.edu)

The culmination of the activity coefficient method is application of the fitted activity coefficients to extrapolate from limited experiments in a Stage III calculation. The recommended order of study is 1) Bubble Pressure; 2) Bubble Temperature; 3) Dew Pressure; 4) Dew Temperature. Note that an entire Txy diagram can be generated with bubble temperature calculations; no dew calculations are required. However, many applications require dew calculations, so they cannot be avoided. The dew calculations are more complicated than bubble calculations, because the liquid activity coefficients are not known until the unknown liquid mole fractions are found. This screencast describes the procedure and how to implement the method in Matlab or Excel.

10.01 - Introduction to Phase Diagrams Click here. 96 5

Introduction to Phase Behavior (9:37) (msu.edu)
Students tend to be distracted with the algorithms for bubble, dew, and flash, and often miss the important concepts of the relation of the calculations to the phase diagram. This screencast discusses the pure component endpoints, the trends in phase behavior at the bubble and dew conditions, and the qualitative relation between the P-x-y and T-x-y diagrams.

Comprehension Questions:

1. Referring to the Txy diagram on slide 3, estimate T, nature (ie. L,V, V+L, L+L), composition(s), and amount of the phase(s) for points: a, b. d, g.
2. Referring to the Txy diagram on slide 3, suppose we had T = 340K and zA = 0.40. Estimate T, nature (ie. L,V, V+L, L+L), composition(s), and amount of the phase(s) for that point.
3. Which component is more volatile, A or B?

07.06 Solving The Cubic EOS for Z Click here. 95 4

1. Peng-Robinson PVT Properties - Excel (3:30) (msu.edu)

Introduction to PVT calculations using the Peng-Robinson workbook Preos.xlsx. Includes hints on changing the fluid and determining stable roots.

Comprehension Questions:

1. At 180K, what value of pressure gives you the minimum value for Z of methane? Hint: don't call solver.

2. At 30 bar, what value of pressure gives Z=0.95 for methane?

3. Compute the molar volume(s) (cm3/mol) for argon at 100K for each of the following?
(a) 3.000 bars (b) 4.000 bars (c) 3.26903 bars.

07.09 -The Molecular Basis of Equations of State: Concepts and Notation Click here. 93.3333 3

Nature of Molecular Interactions - Macro To Nano(8min). (uakron.edu) Instead of matching the critical point, we can use experimental data for density vs. temperature from NIST as a means of characterizing the attractive energy and repulsive volume. A plot of compressibility factor vs. reciprocal temperature exhibits fairly linear behavior in the liquid region. Matching the slope and intercept of this line characterizes two parameters. This characterization may be even more useful than using the critical point if you are more interested in liquid densities than the critical point. In a similar manner, you could derive an EOS based on square-well (SW) simulations and use the SW EOS to match the NIST data(11min), as shown in this sample calculation of the ε and σ values for the SW potential. In this lesson, we learn how to characterize the forces between individual atoms, which may seem quite unreal or impractical when you first encounter it. On the other hand, "nanotechnology" is a scientific discipline that explores how the manipulation of nanostructure is now quite real with very significant practical implications. "The world's smallest movie" shows dancing molecules, (IBM, 2min) demonstrating the reality of molecular manipulation, and the accompanying text explains some of the practical implications. Along similar lines, researchers at LLNL and CalTech have developed 3D printers that can display "voxels" (the 3D analog of pixels) of ~1nm3. That's around 10-100 atoms per voxel. Since 2013-14, chemical/materials engineers have been building nanostructures (TEDX, 13min) in the same way that civil engineers build infrastructure.
Comprehension Questions:
1. What does the y-intercept represent in a plot of compressibility factor vs. reciprocal temperature?
2. What parameter does the y-intercept help to characterize, b or ε?
3. What does the x-intercept represent in a plot of compressibility factor vs. reciprocal temperature?
4. What parameter does the x-intercept help to characterize, b or ε?
5. Apply the SW EOS given in the second video to the isochore at 16.1 mol/L. Do you get the same values for ε/k and σ? Explain.

14.10 Solid-liquid Equilibria Click here. 93.3333 3

SLE using Excel with the M1 model (7min, uakron.edu)

Similar to LLE in Excel, the iteration feature can be used to quickly solve for SLE at multiple temperatures.

Comprehension Questions:
1. Estimate the solubility of naphthalene in benzene at 25C. (a) Use the ideal solution model. (b) Use the MAB model. (ANS. a. 0.306, b. 0.302)
2. Estimate the solubility of biphenyl in nhexane at 25C. (a) Use the ideal solution model. (b) Use the MAB model. 
3. Estimate the solubility of phenol in benzene at 25C. (a) Use the ideal solution model. (b) Use the MAB model. 

01.5 Real Fluids and Tabulated Properties Click here. 90 2

P-V and P-T diagrams (LearnChemE.com) (5:52) Describes distinctions and trends between solid, vapor, liquid, gas.

14.10 Solid-liquid Equilibria Click here. 90 4

Solid-Liquid Equilibria using Matlab (7:17) (msu.edu)

The strategy for solving SLE is discussed and an example generating a couple points from Figure 14.12 of the text are performed. Most of the concepts are not unique to UNIFAC or MATLAB.

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