# Where is X in the Reference Handbook?

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#### sheela34

##### Member
Hello, I'm looking at version 1.5 of the mechanical PE reference handbook. Does anyone know if the thermal conductivity of water is stated anywhere? I have not been able to find it.
Also the thermal conductivity of steel. (I did find iron's though.)

#### sheela34

##### Member
So, I'm wondering at what RH the density in this table 1.2.1 Properties of Air at Atmospheric Pressure is tabulated at since it didn't match specific volume values in ASHRAE Psychrometric Chart No. 1 - Sea Level. Since that margin of error did affect the correct answer on some practice problems. I'm wondering if the same thing would happen on the actual test.

#### sheela34

##### Member
Also wondering if they provide a hard copy of the psychrometric charts for the CBT exam because matching multiple lines up on a display ain't easy...

#### Dr. Barber

##### Well-known member
Also wondering if they provide a hard copy of the psychrometric charts for the CBT exam because matching multiple lines up on a display ain't easy...
No hard copies. Everything is on-screen.

This is from NCEES' official YouTube channel:

#### Dr. Barber

##### Well-known member
So, I'm wondering at what RH the density in this table 1.2.1 Properties of Air at Atmospheric Pressure is tabulated at since it didn't match specific volume values in ASHRAE Psychrometric Chart No. 1 - Sea Level. Since that margin of error did affect the correct answer on some practice problems. I'm wondering if the same thing would happen on the actual test.
That table is for dry air, but what practice problem was affected by this?
Dry air at 70F has specific volume of 13.354 ft^3/lbm and at 100% r.h. air at 70F has specific volume of 13.694 ft^3/lbm. That's a difference of less than 3%.
For 100F the difference in specific volume between 0%rh (14.1 ft^3/lb) and 100%rh (15.1 ft^3/lb) is about 7%.

The answer choices shouldn't be that close.

Last edited:

#### sheela34

##### Member
That table is for dry air, but what practice problem was affected by this?
Dry air at 70F has specific volume of 13.354 ft^3/lbm and at 100% r.h. air at 70F has specific volume of 13.694 ft^3/lbm. That's a difference of less than 3%.
For 100F the difference in specific volume between 0%rh (14.1 ft^3/lb) and 100%rh (15.1 ft^3/lb) is about 7%.

The answer choices shouldn't be that close.
Good to know actually answer choices won't be that close. The question was to find the enthalpy of air at Tdb = 80F and Twb = 67F. The choices were:
- 30.2 btu/lbm
- 30.8 btu/lbm
- 31.5 btu/lbm
- 31.9 btu/lbm

So...1-2% difference in the answers of this practice problem.

#### sheela34

##### Member
No hard copies. Everything is on-screen.

This is from NCEES' official YouTube channel:

Oh nice, do you know if we can move drawn lines around? Because that would help with the SHR.

#### Dr. Barber

##### Well-known member
Oh nice, do you know if we can move drawn lines around? Because that would help with the SHR.

My understanding is that you CANNOT drag lines after drawing them. Makes the SHR protractor pretty much useless.

One person on Reddit did post a technique that seems to work well:

#### Dr. Barber

##### Well-known member
Good to know actually answer choices won't be that close. The question was to find the enthalpy of air at Tdb = 80F and Twb = 67F. The choices were:
- 30.2 btu/lbm
- 30.8 btu/lbm
- 31.5 btu/lbm
- 31.9 btu/lbm

So...1-2% difference in the answers of this practice problem.
How did the density in table 1.2.1 Properties of Air at Atmospheric affect this problem? This is just a straight lookup in the psych chart. Those answer choices do seem to be too close together. Where is this problem from?

#### sheela34

##### Member
How did the density in table 1.2.1 Properties of Air at Atmospheric affect this problem? This is just a straight lookup in the psych chart. Those answer choices do seem to be too close together. Where is this problem from?
Yeah...I was like why try to read this chart when there is a table. This is from the 11th edition of the PPI Mechanical Reference Manual (2001). Bit old since it was passed down to me, but I figured most engineering concepts probably didn't change in the last couple decades. I recently borrowed the 13th edition and noticed they don't even provide the practice problems anymore! I feel I lucked out.

#### Dr. Barber

##### Well-known member
most engineering concepts probably didn't change in the last couple decades.
Well of course not, but by not using updated sources you risk wasting time on irrelevant topics. Get an exam prep guide updated for the current CBT format.

#### sheela34

##### Member
Well of course not, but by not using updated sources you risk wasting time on irrelevant topics. Get an exam prep guide updated for the current CBT format.
No worries, I have also ordered supplementary CBT style practice problem books that I will go through.

#### sheela34

##### Member
What is the difference between using one or the other equation to calculate the NPSHA?

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