NECEES Mechanical PE Reference Manual Released - Page 5 - Mechanical - Engineer Boards
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NECEES Mechanical PE Reference Manual Released

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6 hours ago, Dr. Barber said:

The line for f=0.022 is partially missing.

FE2C8D9A-3C72-420C-9971-FD958E1413DE.jpeg

Thanks for letting us know! I've been studying and haven't found anymore major problems lately.

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3.9.2,  Properties of Aqueous Solutions of Ethylene Glycol:

Units for specific heat are in Btu-°F/lb

thermal conductivity is in Btu-ft-°F/hr-ft^2

This error is on all of the glycol charts including the propylene glycol charts.

There's still data missing from the steam tables.

Table 9.1.15 has thermal conductivity in units of Btu-in/hr-ft^3-°F. They screwed up the units in note a on the same page too.

Looks like someone needs a lesson in units!

Edited by OldSquaw
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The analytical expression to calculate enthalpy of moist air is wrong277617408_ScreenShot2020-01-07at11_19_15PM.png.c5b0ece3f8f3c001ce02ab23be7a0824.png

 

This is the correct one, from ASHRAE Handbook of Fundamentals2048198887_ScreenShot2020-01-07at11_22_23PM.thumb.png.13e2391793e98060aa7f92ae20ba5cf9.png

 

 

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Analytical expression to calculate humidity ratio at saturation is wrong:

55132698_ScreenShot2020-01-08at4_06_32PM.png.8075b4e378539507c2b5602a49a3a6b8.png

 

The correct expression, from ASHRAE Handbook of Fundamentals:

642461776_ScreenShot2020-01-08at4_08_28PM.thumb.png.52804328926470c59cd65d32455ebbf6.png

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@Dr. Barber I assume any new errors you post here are from the updated manual?

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I'm certainly not a vibration expert, but the equation for transmissibilty in 2.15.3 appears to have an extra r^2 term.

Can someone check me on that?

Edited by OldSquaw

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1 hour ago, OldSquaw said:

I'm certainly not a vibration expert, but the equation for transmissibilty in 2.15.3 appears to have an extra r^2 term.

Can someone check me on that?

I'm no expert either, but I agree with you. Screenshot of NCEES manual and of MERM13 for comparison: 

1584519772_ScreenShot2020-01-11at12_37_13AM.png.e5e94921d6b5f40503f7bf4f7191edb1.png

 

MERM13:

1060209360_ScreenShot2020-01-11at12_37_59AM.png.0343b3eb481f0388f45d0266bb361c33.png

 

 

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On 1/10/2020 at 9:45 PM, OldSquaw said:

I'm certainly not a vibration expert, but the equation for transmissibilty in 2.15.3 appears to have an extra r^2 term.

Can someone check me on that?

@OldSquaw and @Dr. Barber

I believe that the equation for transmissibilty in 2.15.3 appears is correct as it is for force transmitted due to base excitation, rather than for force applied to an oscillating mass (through, for example, rotating unbalance).

An equation that is equivalent to 60.55/60.56 from MERM13 appears on page 691 (equation 9.94) of the Fourth Edition of Mechanical Vibrations by S.S. Rao for force applied to an oscillating mass, whereas an equation that is equivalent to the equation that appears in Section 2.15.3 of the NCEES manual appears on page 241 (equation 3.74) of the Fourth Edition of Mechanical Vibrations by S.S. Rao for base excitation.

Basically both the equations in the NCESS manual and MERM13 are correct, but are used for two different methods of exciting the mass.

Hope that helps.

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7 hours ago, DKS said:

@OldSquaw and @Dr. Barber

I believe that the equation for transmissibilty in 2.15.3 appears is correct as it is for force transmitted due to base excitation, rather than for force applied to an oscillating mass (through, for example, rotating unbalance).

An equation that is equivalent to 60.55/60.56 from MERM13 appears on page 691 (equation 9.94) of the Fourth Edition of Mechanical Vibrations by S.S. Rao for force applied to an oscillating mass, whereas an equation that is equivalent to the equation that appears in Section 2.15.3 of the NCEES manual appears on page 241 (equation 3.74) of the Fourth Edition of Mechanical Vibrations by S.S. Rao for base excitation.

Basically both the equations in the NCESS manual and MERM13 are correct, but are used for two different methods of exciting the mass.

Hope that helps.

Ah, ok. Gotcha.

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Section 5.2, units of thermal resistance are wrong.

The units they specify in 5.2.1 (which I highlighted in blue here) are actually units of R-value, which is NOT the same as thermal resistance.

1449825670_ScreenShot2020-01-14at7_13_56PM.png.da4d9636066dcee19b4d1c00682d07fa.png

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Section 5.2.4, the equation for fin heat transfer rate is not correct. If there is negligible heat transfer from the tip, then you use the actual fin length L, not the corrected length Lc. The corrected length is used when calculating fin heat transfer rate for a tip with convection at the tip.

Also, if you use the units for thermal conductivity as specified here, the equation needs a "12" somewhere, or better yet, the units for k should be specified as (Btu/h)/(ft F) and not as (Btu/h) in/(ft^2 F).

 

 

1915012112_ScreenShot2020-01-16at12_23_34PM.png.62d3cabfb8bd376c71c3d3f07f33735f.png

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3 hours ago, Dr. Barber said:

Section 5.2.4, the equation for fin heat transfer rate is not correct. If there is negligible heat transfer from the tip, then you use the actual fin length L, not the corrected length Lc. The corrected length is used when calculating fin heat transfer rate for a tip with convection at the tip.

Also, if you use the units for thermal conductivity as specified here, the equation needs a "12" somewhere, or better yet, the units for k should be specified as (Btu/h)/(ft F) and not as (Btu/h) in/(ft^2 F).

 

 

1915012112_ScreenShot2020-01-16at12_23_34PM.png.62d3cabfb8bd376c71c3d3f07f33735f.png

I have never seen those equations in such an odd form.  Yikes.

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18 hours ago, Audi driver, P.E. said:

I have never seen those equations in such an odd form.  Yikes.

Actually, that's how I've always seen them. Here are snapshots from the heat transfer book by Cengel and from Incropera. The NCEES manual is wrong though, in the use of Lc for the case of negligible heat transfer at the tip.  

283916716_ScreenShot2020-01-17at10_39_23AM.png.0cb18872243facbcc736a3bed267cf45.png

551295958_ScreenShot2020-01-17at10_36_17AM.png.210cad72ada8562572178d43e84b1547.png

 

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The correlation for the Nusselt number for constant wall temperature, laminar, fully developed flow is wrong. As shown in the attachment, they have Nu = 4.66 and it should be Nu = 3.66. I am attaching screenshots from two different heat transfer textbooks to show the correct one. Furthermore, this correlation (as well as the one for constant wall heat flux; Nu=4.36) are valid for fully developed flow only, but the manual does not give the correlations for the entry length, which one needs in order to figure out if the flow is fully developed. ¯\_(ツ)_/¯ 

363005191_ScreenShot2020-01-19at12_49_16PM.png.71e9026689f8ad7117ea05d83e5cd810.png

 

 

Textbook by Incropera et al:

863450734_ScreenShot2020-01-19at12_47_29PM.png.cc37b98ae48fbe146f5d5649b2b57a33.png 

 

Textbook by Cengel: 

2105079459_ScreenShot2020-01-19at12_48_09PM.thumb.png.ad93e82b36f73da2c89d507b16fa6835.png

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When using Q=UAFΔTlm for a "complex" heat exchanger the LMTD is the one as defined for the simple counter-flow tube-in-tube heat exchanger.  The NCEES manual does not specify this. Also, what's the deal with using 2.3 log10(x) instead of ln(x)? I mean, I know it's the same thing, but do they think the approved calculators don't have keys for natural log?

 

 923955958_ScreenShot2020-01-19at3_36_30PM.png.91a1b1432b9bb7aa2888ae261561205e.png 

Edited by Dr. Barber

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29 minutes ago, Dr. Barber said:

Typo in one of the radiation heat transfer equations:

574799838_ScreenShot2020-01-21at8_08_11PM.png.a8078ed180808eed8b523770c38d9c89.png

 

 

921729960_ScreenShot2020-01-21at8_12_37PM.png.f4d59632d336cc82bff828ce6ab1be80.png

 

Dr Barber NCEES seriously needs to pay you for single handedly fixing their screwed up reference manual.

Are you an under cover secret NCEES agent ? 😂😂

Edited by OldSquaw
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12 hours ago, OldSquaw said:

Dr Barber NCEES seriously needs to pay you for single handedly fixing their screwed up reference manual.

Are you an under cover secret NCEES agent ? 😂😂

LOL

 I’m a developer of technical content for @Slay the P.E.. Re-writing all the problems so they can be solved using only the handbook has been... an adventure.
 

Having said that, I’m never acting in an “official” capacity when I’m snarky or when I use profanity and sarcasm 😉 

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2 hours ago, Dr. Barber said:

LOL

 I’m a developer of technical content for @Slay the P.E.. Re-writing all the problems so they can be solved using only the handbook has been... an adventure.
 

Having said that, I’m never acting in an “official” capacity when I’m snarky or when I use profanity and sarcasm 😉 

I know you're doing your work and working to improve @Slay the P.E.'s course content.

But (I'm sure you realized this) you're doing a HUGE favor to mechanical engineers everywhere by submitting these errors to NCEES. 

... I wish/hope someone on the MDM side is getting this deep into finding errors.

Edited by jean15paul_PE
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6 hours ago, jean15paul_PE said:

I know you're doing your work and working to improve @Slay the P.E.'s course content.

But (I'm sure you realized this) you're doing a HUGE favor to mechanical engineers everywhere by submitting these errors to NCEES. 

... I wish/hope someone on the MDM side is getting this deep into finding errors.

Exactly. I would be terrified right now if I had to take the exam using that text.

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On 1/22/2020 at 6:37 PM, Audi driver, P.E. said:

Exactly. I would be terrified right now if I had to take the exam using that text.

Luckily I'm taking the HVAC&R test. From what I can tell, it looks like most of the major issues have been reported and should be fixed soon (for the HVAC&R and probably most of the thermal and fluids stuff). The other key is knowing how to solve problems using (aka not using) this reference manual. I have learned my lesson to ALWAYS check my units and never use the "convenient" equations from the reference manual where the units have been "worked out for you." They are usually wrong.

Hopefully the problems and solutions on the real test are not based on the screwed up reference manual. Because then you could potentially get a problem technically correct but incorrect according to NCEES.

Edited by OldSquaw
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I simply don't see how the exam could be designed to be solved using the reference NCEES has published. To create exam questions, they would certainly have to vet out the problem solution given only the information in the booklet. Either the correct answer will actually be an incorrect answer or the solution will actually require additional information not in the booklet.

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1 hour ago, Audi driver, P.E. said:

I simply don't see how the exam could be designed to be solved using the reference NCEES has published. To create exam questions, they would certainly have to vet out the problem solution given only the information in the booklet. Either the correct answer will actually be an incorrect answer or the solution will actually require additional information not in the booklet.

They specifically say that the solutions could require additional information not in the booklet. 

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8 minutes ago, jean15paul_PE said:

They specifically say that the solutions could require additional information not in the booklet. 

And when info conflicts, then what?

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