NECEES Mechanical PE Reference Manual Released

[Audi Driver P.E.]

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.

 

[OldSquaw]

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.

 

[Audi Driver P.E.]

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.

 

[Tiger15]

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. 

 

[Audi Driver P.E.]

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

And when info conflicts, then what?

 

[OldSquaw]

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.

I’m not sure if this is any help to anyone but I managed to score an 83% on the NCEES practice exam using only the NCEES reference manual. The practice exam is the same as the one that you were allowed to use your own references on. So the new reference manual can be used with some success.

 

[OldSquaw]

I've noticed a recurring error in the PPI practice problems where in the solution to the problem they multiply lbm by the acceleration to get lbf. They neglect to divide by g_c. This error is on every problem that I have encountered where you have to convert lbm to lbf. I just solved a problem, and got it "wrong" of course. Only to find out that according to PPI, a 100lbm object weighs 3,220 lbf on earth.

The whole concept of lbm is completely stupid, but they should at least use it correctly.

 

[Tiger15]

I've noticed a recurring error in the PPI practice problems where in the solution to the problem they multiply lbm by the acceleration to get lbf. They neglect to divide by g_c. This error is on every problem that I have encountered where you have to convert lbm to lbf. I just solved a problem, and got it "wrong" of course. Only to find out that according to PPI, a 100lbm object weighs 3,220 lbf on earth.

The whole concept of lbm is completely stupid, but they should at least use it correctly.

Spoken like a true MDM mechanical engineer! 

SLUGS 4 LIFE  (only half joking)

 

[Tiger15]

I've noticed a recurring error in the PPI practice problems where in the solution to the problem they multiply lbm by the acceleration to get lbf. They neglect to divide by g_c. This error is on every problem that I have encountered where you have to convert lbm to lbf. I just solved a problem, and got it "wrong" of course. Only to find out that according to PPI, a 100lbm object weighs 3,220 lbf on earth.

The whole concept of lbm is completely stupid, but they should at least use it correctly.

Spoken like a true MDM mechanical engineer! 

SLUGS 4 LIFE  (only half joking)

Dr. Tom said something so great in his MDM course. (Paraphrasing) If you see "lb" always it's ALWAYS a force. Even if it says "lbm" treat it like a force. Then you never have to use gc and the units always work out. This approach is 100% effective in MDM problems and is usually simpler.

I think this less effective in TFS. From what I understand: lbm is genuinely useful in solving TFS problems, and if you use it and gc correctly, then it simplifies many problems. 

edit: added the "I think" and "from what I understand" because TFS really isn't my thing.

 

[Dr. Barber]

Dr. Tom said something so great in his MDM course. (Paraphrasing) If you see "lb" always it's ALWAYS a force. Even if it says "lbm" treat it like a force. Then you never have to use gc and the units always work out. This approach is 100% effective in MDM problems and is usually simpler.

This less effective in TFS. lbm is genuinely useful in solving TFS problems, and if you use it and gc correctly, then it definitely simplifies many problems. 

I like the approach of Cengel and Boles in their absolutely wonderful undergrad Thermo book. At Slay the PE this is how we handle this issue because our hate for gc is unparalleled.

 

[OldSquaw]

I like the approach of Cengel and Boles in their absolutely wonderful undergrad Thermo book. At Slay the PE this is how we handle this issue because our hate for gc is unparalleled.

View attachment 16362

My best advice is to abandon the English system of units altogether. I almost never use English units at work. I just convert the answer to English at the end. That's the easiest way to stay out of trouble. But that doesn't work too well on the PE exam, especially the HVAC exam.

 

[Audi Driver P.E.]

I like the approach of Cengel and Boles in their absolutely wonderful undergrad Thermo book. At Slay the PE this is how we handle this issue because our hate for gc is unparalleled.

View attachment 16362

This methodology is superior in exactly every respect. Thank you for proffering this.

 

[OldSquaw]

Page 383 and 385, note 3, Saturation temperature DeltaT for other capacities and equivalent length:

The equation in the NCEES reference manual is DeltaT = Table DeltaT*[(Actual Le/Table Le) * (Actual Capacity/Table Capacity)]^1.8

According to the ASHRAE refrigeration handbook, the equation is supposed to be DeltaT = Table DeltaT*(Actual Le/Table Le) * (Actual Capacity/Table Capacity)^1.8

 

[Dr. Barber]

Page 383 and 385, note 3, Saturation temperature DeltaT for other capacities and equivalent length:

The equation in the NCEES reference manual is DeltaT = Table DeltaT*[(Actual Le/Table Le) * (Actual Capacity/Table Capacity)]^1.8

According to the ASHRAE refrigeration handbook, the equation is supposed to be DeltaT = Table DeltaT*(Actual Le/Table Le) * (Actual Capacity/Table Capacity)^1.8

@OldSquaw Did you report this to NCEES? Just want to check before I do it.

I have a screenshot of 2018 Refrigeration which I get online. NCEES say they copied their table from 2014 Refrigeration, though. Do you have access to that version? I don't. Maybe (doubtful) it changed from 2014 to 2018. I doubt it, but maybe that would explain it.





FYI, I have reported every typo we've discussed in this thread, prior to this post.

 

[OldSquaw]

Yes I reported this to NCEES.

I only have access to the 2018 ASHRAE Refrigeration Handbook.

 

[Dr. Barber]

Fun fact: The handbook is missing page 281, which contains the correlation for Nusselt number for turbulent flow in pipes and the natural convection correlations for vertical plates suspended in a stationary fluid.

 

[Dr. Barber]

Fun fact: The handbook is missing page 281, which contains the correlation for Nusselt number for turbulent flow in pipes and the natural convection correlations for vertical plates suspended in a stationary fluid.

Yeah, never mind. I downloaded it again this morning and that file does have this page. I'm not sure how it went missing from the file I had been working with.

 

[cjohnson]

Is there a comprehensive list somewhere of the known errors in handbook version 1.1, specifically as it pertains to MDM?  I am taking the exam on Monday and would like to review all know errors.

 

[ChooChooEngineer_PE]

Admittedly vibrations are not my strong suite in MDM but noticed this when I was reviewing some topics with a colleague. Seems they added an extra r^2 to the formula when going to  version 1.1

In MERM this term is absent so I'm pretty sure the formula in 1.1 is wrong but someone who knows better please confirm.

 

[Slay the P.E.]

Admittedly vibrations are not my strong suite in MDM but noticed this when I was reviewing some topics with a colleague. Seems they added an extra r^2 to the formula when going to  version 1.1

In MERM this term is absent so I'm pretty sure the formula in 1.1 is wrong but someone who knows better please confirm.

View attachment 18727

This was already clarified in this previous post:

http://engineerboards.com/topic/33324-necees-mechanical-pe-reference-manual-released/?do=findComment&comment=7618245