Your temperatures are inconsistent. YOu have the atmospheric temperature set to 70°F, but also have hard coded 300K (a different temperature) in many places. The result is that the initial pressure in V2 is less than atmospheric pressure, and your equations result in imaginary quantities. I set the temperature to 300K to get a solution.
After that you still need to limit the integration time, as your equations apparently allow the pressure to fall below atmospheric pressure (probably an error, possibly just round off) at which point you get the imaginary results.
Don't use Radau. It is unreliable. The best general solver is the adaptive one.
For posting you should post the worksheet file itself, not a zip file. For size considerations, use the XMCDZ (compressed) format, with the file options set not to include rendered images.
Your equations are a bit confusing, as you copy some complicated expressions rather than use simple functions to express the pressure. I didn't fix that.
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� � � � Tom Gutman
