# Top-rated ScreenCasts

Text Section | Link to original post | Rating (out of 100) | Number of votes | Copy of rated post |
---|---|---|---|---|

05.2 - The Rankine cycle | Click here. | 100 | 1 |
Thermal Efficiency with a 1-Stage Rankine Cycle. (uakron.edu, 12min) Steam from a boiler enters a turbine at 350C and 1.2MPa and exits at 0.01MPa and saturated vapor; compute the thermal efficiency ( η.) This kind of calculation is one of the elementary skills that should come out of any thermodynamics course. Try to pause the video often and work out the answer on your own whenever you think you can. You will learn much more about the kinds of mistakes you might make if you take your best shot, then use the video to check yourself. Then practice some more by picking out other boiler and condenser conditions and turbine efficiencies. FYI: the conditions of this problem should look familiar because they are the same as the turbine efficiency example in Chapter 4. That should make it easy for you to take your best shot._{E}Comprehension Questions: 1. The entropy balance is cited in this video, but never comes into play. Why not? 2. Steam from a boiler enters a turbine at 400C and 2.5 MPa and exits a 100% efficient turbine at 0.025MPa; compute the Rankine efficiency. Comment on the practicality of this process. (Hint: review Chapter 4 if you need help with turbine efficiency.) |

08.08 - Reference States | Click here. | 100 | 1 |
This sample calculation shows how to compute the liquefaction in the Linde process for methane as the operating fluid. (uakron, 8min) The Linde process is a slight variation on the OVC cycle wherein the liquefied fraction exiting the throttle is captured as product and removed from the process. There is also heat integration in the sense that the cold vapor is used to precool the feed to the throttle. FYI: Since natural gas is mostly methane, this process could be easily adapted to the production of liquefied natural gas (LNG) or liquified petroleum gas (LPG, mostly propane). Liquefied gases may seem impractical when you first encounter them, but they are more efficient for transport because they are so much more dense than the gases. Keeping them as liquids is basically a reflection of the effectiveness of the insulation. If any gas leaks from the relief valve (~1.1 bar), then liquid must evaporate to fill the space. The requisite heat of vaporization in that case cools the remaining below the boiling temperature. No heat = no vaporization. |

17.05 - Effect of Pressure, Inerts, Feed Ratios | Click here. | 100 | 1 |
How to push, pull, persuade a reaction (3:32) (msu.edu) Pressure can be used to influence conversion for reactions where gas phase species are present. Feed ratios, inerts, or simultaneous reactions can also be used. Comprehension Questions: 1. The principle by which a change in temperature, pressure, or concentration leads to a counteracting change in equilibrium is known as:_____. |

17.05 - Effect of Pressure, Inerts, Feed Ratios | Click here. | 100 | 1 |
Partial pressures and reactor sizing are among the keys to chemical engineering calculations (uakron.edu, 7 min, review from Section 1.6). Partial pressures (uakron.edu, 7 min) also play an essential role in reaction equilibrium calculations. Partial pressure calculations basically involve straightforward mass balances, but specific vocabulary and a need for systematic precision can cause difficulty. The calculations involve six elements that must be carefully computed:
(1) Stoichiometry - the reaction equation must be stoichiometrically balanced such that the number of atoms of each element are the same on both sides of the equation. This balance is achieved by adjusting the stoichiometric coefficients. The change in the number of moles of each component must be in correct stoichiometric proportions relative to the "key component." Inert compounds (see below) are NOT included in the stoichiometric equation. For the example in this presentation, the objective of the reactor is to oxidize carbon monoxide (CO) in a catalytic converter by reacting it with oxygen (O2). So, CO + 0.5 O2 = CO2.
Comprehension Questions:
1. What is the value of the total pressure (bar) applied in the presentation of this example? |

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 A_{12}*x_{1}*x_{2}. 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: |

11.02 - Calculations with Activity Coefficients | Click here. | 100 | 3 |
Bubble Temperature (2:43) (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 bubble temperature is the easiest after bubble pressure. 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. |

03.3 - Introduction to Mixture Properties | Click here. | 100 | 1 |
Props.xlsx has a lot of data, but usually we are only interested in a few components at a time. Adding a few lines at the top and applying the VLookup function makes it easy to tabulate the properties you need. (8min, uakron.edu) Comprehension questions 1. Download the latest version of Props.xlsx from sourceforge. Add lines to support 8 components of interest and cells to compute Psat given T as input and Tsat given P as input by appropriately arranging Eqn. 2.47. Add a column for computing Hvap at Tsat for each component by Eqn. 2.45. 2. Insert a sheet(tab) called Hrxn in Props.xlsx. Types the names for components in the reaction CO+0.5O2=CO2. Use VLookup to tabulate the Hf values for each component. To the left of the name column, insert cells to represent the stoichiometric coefficients. Then calculate the heat of reaction by using the sumproduct() function applied to the stoichiometric coefficients and Hf values. Check your result with a hand calculation. 3. Download the latest versions of PREOS.xls and Props.xlsx from sourceforge. Update the Props tab appropriately. Then implement the VLookup function on the ThermoProps tab of PREOS so all you need to do is type the name of the compound of interest in order to update the ThermoProps sheet to all properties of interest. We discuss how to use PREOS.xls to solve problems in Unit II. |

07.02 Corresponding States | Click here. | 100 | 2 |
Principles of Corresponding States (10:02) (msu.edu) Comprehension Questions: 1. What is the value of the reduced vapor pressure for Krypton at a reduced temperature of 0.7? How does this help us to characterize the vapor pressure curve? 2. Sketch the graph of vapor pressure vs. temperature as presented in this screencast for the compounds: Krypton and Ethanol. Be sure to label your axes completely and accurately. Draw a vertical line to indicate the condition that defines the acentric factor. |

07.11 - The molecular basis of equations of state: analytical theories | Click here. | 100 | 1 |
Nature of Molecular Parking Lots - RDFs(20min, uakron.edu) Molecules occupy space and they move around until they find their equilibrium pressure at a given density and temperature. Cars in a parking lot behave in a similar fashion except the parking lot is in 2D vs. 3D. Despite this exception, we can understand a lot about molecular distributions by thinking about how repulsive and attractive forces affect car parking. For example, one important consideration is that you should not expect to see two cars parked in the same space at the same time! That's entirely analogous for molecular parking. Simple ideas like this lead to an intuitive understanding of the number of molecules distributed at each distance around a central molecule. From there, it is straightforward to multiply the energy at a given distance (ie. u(r) ) by the number of molecules at that distance (aka. g(r) ), and integrate to obtain the total energy. A similar integral over intermolecular forces leads to the pressure. And, voila! we have a new conceptual route to developing engineering equations of state. |

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. |