# Ideal Gas Law - NCEES Thermo # 502 and 504



## tmacier (Sep 23, 2010)

Good morning,

As I am preparing for the exam I find myself relearning many areas, using the MERM as the main method of teaching.

I am working the NCEES 2008 Thermo problems 502 and 504

The solutions appear to being using a version of PV=nRT that brings area and mass flow rate into it.

Looking thru the MERM I cannot find these associations at all.

Can someone point me to the specific section so I can get a better understanding of these solutions?

Or explain to me what I am missing-

m(dot)=pAV Were did this come from?

m(dot)RT=PAV Were did this come from?

Thanks in advance for your time.

Tim


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## tmacier (Sep 24, 2010)

Nobody can point me to were these formulas are in the MERM?

Tim


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## navyasw02 (Sep 24, 2010)

tmacier said:


> Good morning,
> As I am preparing for the exam I find myself relearning many areas, using the MERM as the main method of teaching.
> 
> I am working the NCEES 2008 Thermo problems 502 and 504
> ...



I'm out of town so I dont have my MERM on me, but the first equation you have listed (mdot = pAV) is the definition of mass flow rate. That should be in one of the first fluids chapters of the MERM. The second one I would think would be in the thermo section that deals with ideal gas, molar weights, and all that jazz. Again, I dont have my book on me, but that's where I'd start looking.


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## Baltimore Joe (Sep 24, 2010)

tmacier said:


> Good morning,
> As I am preparing for the exam I find myself relearning many areas, using the MERM as the main method of teaching.
> 
> I am working the NCEES 2008 Thermo problems 502 and 504
> ...


The continuity equation is 17.1 and 17.2. The other equation you references is just substituting the ideal gas law into the continuity equation by replacing density (p) with the term P/RT.


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## NerdHerd (Sep 29, 2010)

Baltimore Joe said:


> tmacier said:
> 
> 
> > Good morning,
> ...


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## tmacier (Oct 2, 2010)

Thanks guys -

I am getting triped up on the basics -

27 days left -

Tim


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