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Old 10-05-2012, 09:46 AM   #76
WDE46
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Quote:
Originally Posted by SeanC View Post
Why do you need two sets of P and T? One set is not only redundant, but will also bias the results. For example, barometric pressure P1 is not the same everywhere, and what value of T1 you choose? It is arbitrary.


That's what I am trying to convey to you. The situation is simpler than you think it is. You only need a single temperature value to calculate the pressure in this case.
I am trying to work with the same methods an engineer designing the system may have used. So I use a minimum temperature and pressure (room temp/1 atm),then I use the operating temperature. Then I solve for the operating pressure. I just used some more assumptions, but they are perfectly valid for most cases. I didn't have to look anything up to do it either.

I used 101.325 kPa for P1 and 293.15 K (20C) for P2 then 373.15 (100C) for T2. It gives me 128.98 kPa, which is close to your number, so our math checks out. I just don't see how you got the 1.35 atm number without using the equation I used. If you used the gas equation you would need to know volume, which we don't. What am I missing here?

Last edited by WDE46; 10-05-2012 at 09:50 AM.
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