NECEES Mechanical PE Reference Manual Released

[Dr. Barber]

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

 

[YW55]

Taking the April 2019 MDM exam and printed out the first 200pgs of this reference manual as a quick reference and have MERM, Kennedy and Shigley's as backups. The MDM section heavily relied on the Shigley book for reference. Went through all the MDM section in the manual line by line to make sure I'm familiar with the material. Nothing surprising on there if you have done section 45 to 60 on MERM.

My weak point will be Quality Control/Statistics so I'll be concentrating on that before the exam.

 

[Audi Driver P.E.]

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

View attachment 12674​

...but the saturated vapor table in the handbook begs to differ:

View attachment 12675​

 ​

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

I haven't looked. Have they published any errata for this yet?

 

[Dr. Barber]

I haven't looked. Have they published any errata for this yet?

Not as far as I can tell. I've just sent them a message about these issues with their steam tables.

 

[ChooChooEngineer_PE]

So I see here that no errata has been posted for the PE ref manual. Don't know if anyone else but me decided to practice with it for the MDM practice test. Page 178, the configuration for the weld you need on the exam problem has b and d flipped. I'm sitting here banging my head against a wall thinking how is it a 1" weld I need? Used the right Ju equation and no problem. has anyone checked the other weld groups for correct Ju formulas? The manual has some nice info and I'd want to use it but if this is wrong, what else is? Thanks in advance.

 

[Dr. Barber]

So I see here that no errata has been posted for the PE ref manual. Don't know if anyone else but me decided to practice with it for the MDM practice test. Page 178, the configuration for the weld you need on the exam problem has b and d flipped. I'm sitting here banging my head against a wall thinking how is it a 1" weld I need? Used the right Ju equation and no problem. has anyone checked the other weld groups for correct Ju formulas? The manual has some nice info and I'd want to use it but if this is wrong, what else is? Thanks in advance.

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:

 

[Audi Driver P.E.]

Folks with an interest in the exam better start piping up to NCEES about this, because this seems like a pretty big Charlie Foxtrot from my vantage point.

 

[Dr. Barber]

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)

 

[Dr. Barber]

Folks with an interest in the exam better start piping up to NCEES about this, because this seems like a pretty big Charlie Foxtrot from my vantage point.

I've been sending them the errata I"ve been posting here.

 

[Dr. Barber]

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.

 

 

[Dr. Barber]

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

 

[YW55]

The entire welding table is a big fail, I couldn't get a practice question right last night and found out why. At this point I'm extremely hesitant on using this as a reference for the April 2019 test coming up.

 

[23and1]

Yeah, I've ABSOLUTELY changed my mind about using this reference for the upcoming exam

 

[Audi Driver P.E.]

Yeah, I've ABSOLUTELY changed my mind about using this reference for the upcoming exam

I know I wouldn't use it.

 

[Dr. Barber]

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

View attachment 12690

From Shigley's:

View attachment 12691

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.

 

[ChooChooEngineer_PE]

The galvanic series in it is also off when compared to MARKS and MERM.

 

[YW55]

For the Johnson's Intermediate columns formula, some references omits the K factor while some references uses K^2 instead of K. I'm confused on which one is the right equation.

 

[YW55]

Spring Ks factor equation is different than MERM and Kennedy's book. It gets you close enough number though. Makes you wonder which formula NCEES exam makers are using.

 

[Ramnares P.E.]

Spring Ks factor equation is different than MERM and Kennedy's book. It gets you close enough number though. Makes you wonder which formula NCEES exam makers are using.

View attachment 12748

The Ks defined is the Wahl factor which is well known in the spring manufacturing industry.  Also, refer to Shigley who also defers to the Wahl factor.

 

[YW55]

The Ks defined is the Wahl factor which is well known in the spring manufacturing industry.  Also, refer to Shigley who also defers to the Wahl factor.

Which is 

 correct? I'm not sure where the reference manual got the other equation from.