# Low Pressure air



## Lily (Oct 3, 2010)

Hi everyone,

I realized that I almost never used Appendix 24F (Properties of low pressure air) while preparing for the MD PE. What kind of problems are we supposed to used this appendix for and what pressure is considered a low pressure for air?

Thanks and good luck for your preparation.


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## NerdHerd (Oct 5, 2010)

Lily said:


> Hi everyone,I realized that I almost never used Appendix 24F (Properties of low pressure air) while preparing for the MD PE. What kind of problems are we supposed to used this appendix for and what pressure is considered a low pressure for air?
> 
> Thanks and good luck for your preparation.


___________

Hello Lily,

I’ve used the low pressure air tables in Thermo: First Law – when analyzing an air compressor operating at stead state. When given the inlet and outlet pressures and temperatures, you can look up the enthalpy at each state then “plug and chug” …after converting everything else, hehehe =)

SMS Thermal and Fluids #20 utilizes this.

Good luck!

NerdHerd


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## Lily (Oct 5, 2010)

Thanks NerdHerd,

I will check out this SMS problem tonight,

Does anyone knows what is the max pressure, above which we cannot use this table?

Lily


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## HokieGirl (Oct 14, 2010)

Lily,

I have a note in my book that I added that said "use when less than several hundred psi." That probably doesn't help much, but that was my guideline.

Good luck!


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## Lily (Oct 16, 2010)

Thanks!

I think the values in the MERM appendix should be ok for pressures less than 300 psia.

Lily


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## abourne (Oct 26, 2010)

2008 NCEES Thermo - Problem 517

This problem solves for Q_in combuster using the ideal gas laws.

You can solve this using Appendix 24.F MERM as an alternative, finding the enthalpies h_in and h_out of the combuster.

Either way, you'll get the same answer.


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