cyrus15, thanks for the reply.
I stand corrected on the car fuel pumps, I appreciate the links.
Now back to relevant matters.
Originally Posted by cyrus15
Yes, that is the document I was referring to.
The vapor pressure is 0.029 psia, that is equivalent to 200 Pascal (Pa) you mentioned but that is in Absolute pressure reading (almost in vacuum condition). Meaning; you can’t mix absolute pressure and atmospheric pressure readings without the proper conversion.
That is only partially correct. It is an absolute pressure if the gas is the only gas in the "atmosphere", but if there is another gas present, this value is also the
partial pressure of that substance in the gas mixture. That's how gases work.
To do so, we should get the vapor pressure at the corrected temperature added to the ambient pressure at also the corrected temperature and altitude to get the pressure inside the fuel tank at that altitude.
What would create the ambient pressure inside the tank, to which you add the vapor pressure?
This only applies under very specific conditions, namely that there was atmopheric pressure in the vessel to begin with, created by some other gas, then you add some JP-8. In that case you are correct, we have to add both pressures, and some portiion of the vapor/air mixture would be vented to equalise inside and outside pressure.
So, according to your figures (assuming it is temperature and altitude corrected) we should have 200Pa + 50000Pa to get the pressure inside the fuel tank at 13000 feet, that's why tank vent is needed to allow the 50000 Pa to get in the tank though in real life, the tank pressure is little higher than ambient pressure because of the vapor pressure, that’s the correct solution to the exercise.
So,
what is creating the 50,000Pa inside the fuel tank, if not air?
(Hey, finally I also got to use that smiley!
)
I guess it must be
Phlogiston.
Bernd