Top-rated ScreenCasts

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07.11 - The molecular basis of equations of state: analytical theories Click here. 100 1

Nature of Molecular Energy - Example Calculation(8min, uakron.edu) Given an estimate for the radial distribution function (RDF) integrate to obtain an estimate of the internal energy. The result provides an alternative to the attractive term of the vdW EOS.

10.07 - Nonideal Systems Click here. 100 1

This screencast shows how to quickly visualize Pxy phase diagrams for nonideal systems using Excel (5min, uakron.edu). These sample calculations for methanol+benzene apply the simplest nonideal solution model: ΔHmix = A12*x1*x2. Rigors of this model are discussed in Chapter 11. Nevertheless, its basic elements are simple enough that they can be understood in Chapter 10. When x1=0 or x2=0, a pure fluid is indicated, corresponding to no mixing and zero heat of mixing. When A12=0, the ideal solution approximation is recovered. When A12>0, the model indicates an endothermic interaction (like 2-propanol+water, Fig. 10.8c), giving rise to "positive deviations from Raoult's Law." When A12<0, the model indicates an exothermic interaction (like acetone+chloroform, Fig. 10.9c), giving rise to "negative deviations from Raoult's Law." With this spreadsheet, you can quickly change your components and A12 values to see how the phase diagram changes and gain "hands-on" familiarity with the principles discussed in Section 10.7. 

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. Make a Pxy diagram for cyclohexane+toluene at 80C and A12=200. What kind of system is this?
2. Make a Pxy diagram for cyclohexane+benzene at 80C and A12=200. What kind of system is this?
3. Why does the system's qualitative behavior change so much when the components and model parameters are changed so little?

01.5 Real Fluids and Tabulated Properties Click here. 100 1

When you use a spreadsheet like Steam.xlsx(uakron, 15min), interpolation can be greatly expedited. It is recommended that you enable the solver before applying Steam.xls.

Comprehension Questions:
1. Compute H if given T=275 C and P=0.45MPa.
2. Compute H if given T=275 C and V=0.555m3/kg.
3. Which would be more practical for solving a project, double interpolation or steam.xlsx?

09.04 - Changes in Gibbs Energy with Pressure Click here. 100 1

Gibbs Energy - Nuts to Soup. (learncheme.com, 8min) It is straightforward to start from the definition of Gibbs Energy and derive all the changes in Gibbs energy. These can be graphed for H2O to see how familiar quantities from the steam tables relate to changes in this unfamiliar property.

10.07 - Nonideal Systems Click here. 100 1

Nonideal Mixtures (4:58) (msu.edu)

Raoult's law is an easy way to calculate VLE, but it is inaccurate for most detailed VLE calculations. This screencast provides an overview of the problems, and introduces the concept of an azeotrope. The VLE K-ratio is shown to be less than one or greater than one dependenting on the overall system concentration relative to the azeotrope composition where K=1. The concept of positive and negative deviations is introduced.

10.06 - Relating VLE to Distillation Click here. 100 2

Distillation is the primary choice for separations in the petrochemical industry. Because the majority of chemical processing involves separations/purifications, that makes distillation the biggest economic driver in all of chemical production. Therefore, it is very important for chemical engineers to understand how distillation works (21min, uakron.edu) and how VLE plays the major role. This video is a bit long, but it puts into context how phase diagrams and thermodynamic properties relate to very important practical applications. You may find it helpful to reinforce the conceptual video with some sample calculations.(12min) At the end of the video, you should be able to answer the following:

Consider the acetone+ethanol system. Use SCVP (Eqn 2.47) to answer the following.

  1. Sketch a Txy diagram for acetone+ethanol at 1 bar with accurate Tsat's. Label completely.
  2. Which component pertaining to #1 would have enhanced concentration in the distillate?
  3. Accurately sketch the yx diagram pertaining to #1
  4. Use Raoult's Law to estimate αLH pertaining to #1.
  5. Use your sketch from 3 to estimate Nmin  to go from x1=0.1 to 0.9.
  6. Use the Fenske equation to estimate Nmin  with splits of 0.9 and 0.1.
04.09 Turbine calculations Click here. 100 2

Entropy Balances: Solving for Turbine Efficiency Sample Calculation. (uakron.edu, 10min) Steam turbines are very common in power generation cycles. Knowing how to compute the actual work, reversible work, and compare them is an elementary part of any engineering thermodynamics course.

Comprehension Questions:

1. An adiabatic turbine is supplied with steam at 2.0 MPa and 600°C and it exhausts at 98% quality and 24°C. (a) Compute the work output per kg of steam.(b) Compute the efficiency of the turbine.

2. A Rankine cycle operates on steam exiting the boiler at 7 MPa and 550°C and expanding to 60°C and 98% quality. Compute the efficiency of the turbine.

01.6 Summary Click here. 100 1

The objectives for Chapter 1 were:

1. Explain the definitions and relations between temperature, molecular kinetic energy,
molecular potential energy and macroscopic internal energy, including the role of intermolecular potential energy and how it is modeled. Explain why the ideal gas internal energy
depends only on temperature.
2. Explain the molecular origin of pressure.
3. Apply the vocabulary of thermodynamics with words such as the following: work, quality,
interpolation, sink/reservoir, absolute temperature, open/closed system, intensive/extensive
property, subcooled, saturated, superheated.
4. Explain the advantages and limitations of the ideal gas model.
5. Sketch and interpret paths on a P-Vdiagram.
6. Perform steam table computations like quality determination, double interpolation.

To these, we could add expressing and explaining the first and second laws. Make a quick list of these expressions and explanations in your own words, including cartoons or illustrations as you see fit,  starting with the first and second laws.

10.08 - Concepts for Generalized Phase Equilibria Click here. 100 1

When expressing the derivative of the total Gibbs energy by chain rule, there is one particular partial derivative that relates to each component in the mixture: the "chemical potential." By adapting the derivation from Chapter 9 of the equilibrium constraint for pure fluids, we can show that the equilibrium constraint for mixtures is that the chemical potential of each component in each phase must be equal. That is fine mathematically but it is not very intuitive. By translating the chemical potential into a rigorous definition of fugacity of a component in a mixture, we recognize that an equivalent equilibrium constraint is that the fugacity of each component in each phase must be equal. (8min, Live, uakron.edu) This offers the intuitive perspective of, say, molecules from the liquid escaping to the vapor and molecules from the vapor escaping to the liquid; when the "escaping tendencies" are equal, the phases experience no net change and we call that equilibrium. 

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?

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