NECEES Mechanical PE Reference Manual Released

[OldSquaw]

The line for f=0.022 is partially missing.

View attachment 15619

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

 

[OldSquaw]

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!

 

[Dr. Barber]

The analytical expression to calculate enthalpy of moist air is wrong

This is the correct one, from ASHRAE Handbook of Fundamentals

 

[Dr. Barber]

Analytical expression to calculate humidity ratio at saturation is wrong:



The correct expression, from ASHRAE Handbook of Fundamentals:

 

[Audi Driver P.E.]

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

 

[Dr. Barber]

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

Correct. Version 1.1

 

[OldSquaw]

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?

 

[Dr. Barber]

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: 



MERM13:

 

[DKS]

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.

 

[Dr. Barber]

@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.

 

[Dr. Barber]

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.

 

[Dr. Barber]

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).

 

[Audi Driver P.E.]

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).

View attachment 16008

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

 

[Dr. Barber]

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.  

 

[Dr. Barber]

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)_/¯ 



Textbook by Incropera et al:

 

Textbook by Cengel: 

 

[Dr. Barber]

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?

  

 

[Dr. Barber]

Typo in one of the radiation heat transfer equations:

 

[OldSquaw]

Typo in one of the radiation heat transfer equations:

View attachment 16078

View attachment 16079

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 ?

 

[Dr. Barber]

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  

 

[Tiger15]

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.