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Slay the P.E.

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Slay the P.E. last won the day on October 7 2018

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About Slay the P.E.

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    Prospect Heights, IL
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    Mechanical Engineering Exam Prep

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  1. We've added a two-part series on refrigeration, covering: Ideal Vapor Compression Cycle,. Multi-Stage Vapor Compression and the Ideal Gas Refrigeration Cycles. Access them for free here:
  2. This was already clarified in this previous post:
  3. We have now uploaded video tutorials for the Carnot Cycle, the Brayton Cycle, and the Combined Gas-Vapor Power Cycles. Access them for free here:
  4. Good catch. It appears that of the highlighted values, only the one for 64F is incorrect (it should be 0.3 psia). Did you report this to them?
  5. Update: We just uploaded a 3-part series on Entropy, Entropy Balances, Isentropic Processes and Isentropic Efficiency, as well as a tutorial on the Mollier and P-h Diagrams.
  6. No. Just never use ideal gas assumptions for steam. It’s safer that way. Use tables or a Mollier diagram. For this particular problem: If you start at 3 psia and compress, there is some liquid present at the “inlet” therefore that liquid-vapor mixture is far from being an ideal gas. So that’s a huge no-no. Even if you start with saturated or slightly superheated vapor at 3 psia (a condition in which the steam arguably behaves like an ideal gas) you are taking it to a condition of pressure high enough so the deviation from ideal gas behavior is significant, so whatever it is you’r
  7. 1. With the inlet conditions, find the enthalpy at the inlet, h1, and entropy at the inlet, s1 2. The entropy at the discharge for the isentropic process (s2s) is the same as s1, so for the isentropic process you have s2s and pressure. 3. Is s2s < sg at 3 psia? If yes, you have a saturated mixture at the end of the isentropic process. Calculate quality at the end of the isentropic process, x2s 4. With x2s find the enthalpy at the exit of the isentropic process h2s 5. With h2s and the definition of isentropic efficiency find the enthalpy at the discharge of the actual pro
  8. Dense gases such as steam in power plants and refrigerants in refrigeration cycles in general cannot be modeled as ideal gases. Only when the pressure is VERY low can steam be treated as an ideal gas (this is done in psychrometrics, where the partial pressure of water vapor is in the order of less than 2 psia or so). You have comprehensive steam tables available. Use them and avoid catastrophic mistakes like the one you described.
  9. Really hard to say. Maybe the end of this fall.
  10. Thanks! Yes, it was left out for the sake of brevity. I think we will have a short tutorial just on linear interpolation. Oh, absolutely yes. We’ve been advocating for Mollier diagrams here for the longest time. That video (just on how to use h-s and P-h diagrams) will come after entropy and isentropic efficiency are introduced.
  11. We have been developing video tutorials for the TFS exam. When we finish all of them, we will put them behind a paywall and offer a course based on these videos. For now, as we develop them they will be free. There will be roughly about 50 videos to cover all of TFS. As of the writing of this post, the first 7 are ready and in our website. No video will ever be longer than 10 minutes, to keep your attention focused. The dynamic will be to watch a short video and immediately solve problems associated with the video before moving on to the next one. We're looking for honest constructiv
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