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Dr. Barber

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About Dr. Barber

  • Rank
    Intern

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  • Engineering Field
    Mechanical
  • License
    PE
  • Discipline
    Mechanical

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  1. I have reviewed this and although the expressions I highlighted here in purple appear to be different, it turns out they really aren't. Takes some algebra, but it can be shown that they're the same. So, I'm taking this back. Looks like they got this one right.
  2. Train wreck city, baby. Thermal efficiency of the Otto cycle is wrong: Compare to Thermo textbook by Cengel and Boles (shown here) or equation 28.42 of MERM13
  3. The clusterfudge continues... COP for dual-stage vapor compression refrigeration cycle is wrong. The mass flow rate through the low pressure circuit in a dual-stage system is never the same as that of the high pressure circuit. See example 4 in ASHRAE Fundamentals, Section 2.5 "MULTISTAGE VAPOR COMPRESSION REFRIGERATION CYCLES" The expressions for COP of the system shown in page 264 of the handbook should have the mass flow rates included. COPREF = m5(h5 - h8)/[m1(h2-h1) + m5(h6-h5)] where m5 = mass flow rate of refrigerant through low pressure circuit and m1 = mass flow rate of refrigerant through high pressure circuit. It looks like the authors of the manual assumed that m5 = m1 to obtain their expression. Like I said, this is wrong.
  4. I've been sending them the errata I"ve been posting here.
  5. COP for the gas refrigeration cycle (page 265) is wrong. Here is the correct definition from the Thermodynamics textbook by Cengel and Boles (also, see equation 33.17 in MERM13)
  6. Haven't done a thorough check of the table in page 178, but here it is side by side with its equivalent from Shigley's so you can compare the Ju equations: (the highlighted ones seem different) From the NCEES Handbook From Shigley's:
  7. Not as far as I can tell. I've just sent them a message about these issues with their steam tables.
  8. Simple question: What is the specific volume of saturated water vapor at 2 psia? The superheated vapor tables in the handbook have a line for the saturated liquid and one for the saturated vapor. From this table, vg(2 psia) = 192.368 ft3/lb ...but the saturated vapor table in the handbook begs to differ: The saturation values in the superheated vapor table (6.3.3) are wrong. The right answer by the way is 173.7 ft^3/lbm confirmed by the table in MERM13 and the NIST ChemistryWeb site. https://webbook.nist.gov/cgi/fluid.cgi?Action=Load&ID=C7732185&Type=SatT&Digits=5&PLow=2&PHigh=2&PInc=1&RefState=DEF&TUnit=F&PUnit=psia&DUnit=lbm%2Fft3&HUnit=Btu%2Flbm&WUnit=m%2Fs&VisUnit=uPa*s&STUnit=N%2Fm
  9. I hope CBT takers never are asked to find the entropy of a saturated liquid-vapor mixture of water at 100 psia.
  10. I don't have it memorized, so I'm lucky they were smart enough to include it. I'm also grateful they made some room for these ever useful trig identities. I mean, these are crucial for the P.E. exam:
  11. Yeah, no Mollier diagram which is a major bummer. However, they did put in some really useful and important stuff such as the charge of an electron, Faraday's constant, and the conversion factor from hectares to acres. ¯\_(ツ)_/¯
  12. Like you said, there are only "principles" and "applications" sections. There is no "breadth" or "depth" sections specified anywhere. Strength of materials is in "Principles" and design of machine elements is in "applications", so I don't understand your question.
  13. Seriously? What does your diagnostic report say under: Hydraulic and Fluid Applications > Hydraulic and Fluid Equipment > Actuators
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