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>>The basis of our math is MOLE volume based.
>>Thus the true volume of the cylinder is VERY important.
>>But, give or take 1/2 cubic inch, probably won't make a huge differance.
>
>Forgive me for saying this but I think you are seriously
>confused about what your program does and how it works.
>Unless of course it does depend on the tank volume in which
>case you'll never get within 5% of anything.
>
>My whole point is that the true tankvolume is scaled out
>of *all* equations exactly because your math is purely
>based on N/V = nxA/nxv=A/v = inverse density.
>(v being volume per mole and n the number of moles).
>
>
>Now *input* the temperature of the gas in the tank and out
>comes the pressure. If your program does not work this
>way please tell us *exactly* how it works and why you
>think it's correct to do it that way. Now it's possible
>that knowing the volume of the tank saves you some numeric
>work in the program but I don't see how.
>
>john
John:
This is a short note that the programmer sent to me with the beta code for
the gas mixing program.
Possibly it will be of some help in answering your question..
Please keep in mind, these are just some of his comments to me about how he
went about implementing the B-B equation.
My ideas for pumping high pressure nonideal gases were:
1. the gases are well mixed
2. the starting temp was 20 oC
3. the starting press was 1 atm for air and 500 psi for other gases
4. the basis of calculations will be pumping the proper number of
moles of each gas starting with O2 or N2 depending on the
percents required. the program will calc the appropriate
amount of O2 or N2 and the remainder of air
5. the calculations go for the total pressure requested, no matter
what the temp turns out to be....usually hot....so when the
tank cools, you will have less than the asked for pressure
(this could be changed by fixing a loop)
6. the program canculates the approximate number of moles total,
just to get started....then adjusts the total moles later to
adapt to get the proper pressure, because initially one
gets into an over pressure situation
7. the program runs on an increment of one mole of gas being pumped
in the order given... so pump one mole of gas... calculate
specific volume, and with temperature use the monster
equation of (gas) state and find z and then the actual
pressure. Using joule thompson's coefficient (dt/dp) (I
used the one for nitrogen) caluclate the rise in temp.
then etc....pump another mole of gas canculate new specific
volume and pressure and new temp....etc....until all the moles
of each gas have been added.
8. at this point, check the total pressure....which will be too high.
estimate the total moles required again (lower value) and do
7 again and again until the total pressure is close to that
requested.
9. then print the results and ask for questions
10. A questionable assumption is about Kay's rule, which says that
the parameters of the B-B equation are just a sum function
of the mole fraction of each gas times its coefficient
....this may or may not be true... but this is the method
from which I calculated the B-B coefficients for mixtures....
11. Also I toyed with calculating the dt/dp value from the B-B
equations, but it seemed the value went negative for
the Nobel gases and so the final temps came out much lower
than this version. Some real pumping data would be
helpful here.
Christopher M. Parrett, President, Abysmal Diving Inc.
Makers of ABYSS, Advanced Dive Planning Software.
6595 Odell Place, Suite G. Boulder CO, 80301
Ph, 303-530-7248, Fx, 303-530-2808
ftp://abysmal.com/users/abysmal http://www.emi.net/gulfstream/abyss/abyss.html
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