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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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    Principal in Charge

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    www.slaythepe.com

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  • Location
    Prospect Heights, IL
  • Interests
    Mechanical Engineering Exam Prep

Previous Fields

  • Engineering Field
    CONSULTING
  • License
    PE
  • Discipline
    Mechanical

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  1. Slay the P.E.

    Relative roughness of a pipe?

    Yes, tables usually give a range and also a "design" value (See Appendix 17.A in page A-48 of MERM13. I'm not sure what the "PE Handbook" that you're referencing is, but in MERM13, the Moody Diagram of page 17-7 doesn't have a table). But anyway, you're right. Values are typically listed as ranges. So, what to do? Let's look at the problems in the Thermal and Fluid Systems practice exam from NCEES that use a friction factor or a friction head loss: Problem 126: They say "smooth pipe" but they also just give you the friction head, so no need to calculate the Darcy friction factor. Problem 133: You're asked to calculate the friction head loss, but you don't have enough info to use the Darcy equation. You find hf from the definition of NPSH. So no need to calculate the Darcy friction factor. Problem 505: The friction factor is given in the problem statement, so there's no need to calculate the Darcy friction factor. Problem 515: The friction loss is given, so there's no need to calculate the Darcy friction factor. Problem 519: The friction factor is given in the problem statement, so there's no need to calculate the Darcy friction factor. I notice a pattern 🤔 I suspect that most likely you won't need to calculate a friction factor with a Moody chart in the test. HOWEVER, if you do, I strongly suspect they will tell you exactly which roughness e to use because given the ambiguity in the ranges, you will not land on the correct multiple-choice answer unless you use their same roughness. Finally, if push comes to shove and you find yourself having to calculate a friction factor and they are not explicitly giving you a roughness in the problem statement then the safest bet is to use the "design" value from Appendix 17.A
  2. Slay the P.E.

    question about orifices and tank draining

    They're taking Environmental Engineering exam, per their profile.
  3. Slay the P.E.

    question about orifices and tank draining

    It's exactly the same one you posted from the solution in your book. The one with the difference of the square roots of the heights.
  4. Slay the P.E.

    question about orifices and tank draining

    The equation you attempted to use is for steady state, which is achieved only when: the fluid being drained is replenished at the same rate at which it is leaving through the orifice, or the volume of fluid in the tank is so large that one assumes the water level remains constant during the period of interest. Neither one of the above apply for the problem you posted. In that problem, you have a transient effect, and there is no other way to solve it other than considering time-dependent effects. The equation they used in the solution is derived in page 17-19 of the MERM13 and it is equation 17.83. It is a time-dependent solution.
  5. Slay the P.E.

    TFS practice problem of the week...

    Don’t know if people are aware of this thread. We won’t be adding more problems to it, but all problems here are still very relevant.
  6. Slay the P.E.

    MD&M practice problem of the week

    We won't be adding any more problems to the "practice problem of the week" threads. However, the threads are still here in the boards and are relevant, not just because of the problems themselves but also because of the lively discussion.
  7. Slay the P.E.

    Fluid Mechanics & Hydraulics for TFS Contest

    Thanks! buying our books is the best way to prepare to tackle it wink, wink, nod, nod.
  8. Slay the P.E.

    Fluid Mechanics & Hydraulics for TFS Contest

    This problem appears in our Fluid Mechanics & Hydraulics book. Here's the solution from the book. Let me know if you have any questions. Thanks,
  9. Slay the P.E.

    Steam Table Metric Units

    Quick update on this. The link for the USCS units is no longer working, but I found the same table that used to lead to, here: https://www.bbpsales.com/wp-content/uploads/2017/01/3A-Appendix-Steam-Tables.pdf The link provided by @Audi driver, P.E. for the SI tables from NIST is still functional (but it wasn't during the recent government shutdown). The moral of the story is download them, print them, and save them.
  10. The NCEES handbook for the FE exam is available for free download. It is reasonable to assume they’ll make their PE handbook available for download as well. Maybe they’ll charge for it; maybe not. ¯\_(ツ)_/¯
  11. The exams will be closed book, like the FE and the only reference allowed will be their on-screen PDF handbook. This will make it a lot easier to prepare, especially the HVAC&R folks. I bet we will never see another post here asking if one really needs all ASHRAE books or if older ASHRAE books are good enough.
  12. Slay the P.E.

    Fluid Mechanics & Hydraulics for TFS Contest

    We have received all valid entries. thanks!
  13. Slay the P.E.

    TFS 2016 NCEES Problem 533

    More on this for the truly nerdy:
  14. Slay the P.E.

    TFS 2016 NCEES Problem 533

    At those conditions you have a compressed liquid (the pressure is higher than the saturation pressure at the given temperature). There are compressed liquid tables, but those tables start at fairly high pressure values.  The alternative then is to use the “saturated liquid approximation” — that is the enthalpy of a compressed liquid is approximately the same as hf for the liquid’s temperature. For 25psi and 100F we say that the enthalpy is simply hf @ 100F. See our Thermo book for a more complete discussion of the saturated liquid approximation. In MERM13 the compressed liquid water table is Appendix 23D in page A-69. The lowest pressure listed, however, is 200 psi. Therefore, for compressed liquid water at 25 psia, 100F you have to use the saturated liquid approximation. If you check the saturated water table, you'll see that hf(T=100F)=68.03 Btu/lbm. .
  15. Slay the P.E.

    Fluid Mechanics & Hydraulics for TFS Contest

    Well, why not? Let's do this again y'all. This time the first three to submit the right answer ( via private message here or via email to customersupport@slaythepe.com ) will get the 50% off our ebook bundle which now includes a book on Heat Transfer and Heat Exchanger Analysis. The four books combine for 280+ problems in Thermodynamics & Energy Balances, Fluid Mechanics & Hydraulics and Fluid Applications, Psychrometrics and Mass Balances, and Heat Transfer & Heat Exchanger Analysis in 550+ pages of step-by-step solutions and detailed explanations. Get free sample pages to preview the books HERE.
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