New Bug Reports/Feature Requests

[Richard Houser]

It may be overkill, but if going far enough to find a regression equation, should the specific gas mix be taken into account?

Please note that I have no idea if this table is correct or not for any of the listed gasses: http://www.baue.org/library/zfactor_table.php

On February 24, 2016 2:18:42 AM EST, Linus Torvalds <torvalds at linux-foundation.org> wrote:
>On Feb 23, 2016 15:46, "Linus Torvalds" <torvalds at linux-foundation.org>
>wrote:
>>
>
>>  (b) air is not actually entirely compressible.
>>
>>      This is a fairly small factor at 3000psi, but it's a factor.
>> HOWEVER. The rule for cylinder sizing is that the stated cylinder
>size
>> is basically the "theoretical" size, not the real size.
>
>Actually, doing the math, the compressibility of air is enough to
>bring that 80 cuft down to about 78 cuft. So that may actually be the
>biggest effect.
>
>We currently approximate the gas volume as being linear below 200 bar,
>and eat that up-to-3% error.
>
>Maybe we could do better.
>
>Does somebody have curve fitting software to generate a better
>function for the air compressibility factor? From Wikipedia (staying
>at 300K, which is warm water), we have
>
>   bar    compressibility
>   ---    ---------------
>     1    0.9999
>     5    0.9987
>    10    0.9974
>    20    0.9950
>    40    0.9917
>    60    0.9901
>    80    0.9903
>   100    0.9930
>   150    1.0074
>   200    1.0326
>   250    1.0669
>   300    1.1089
>   400    1.2073
>   500    1.3163
>
>and we could probably do better than our current "linear plus
>second-order" approximation.
>
>Somebody with R (or matlab) could probably get a reasonable curve from
>the above data. With a function for the compressibility factor, we
>could improve on our current "gas_volume()" function.
>
>Of course, we could also just do it the stupid way and do the above
>table and just do linear interpolation in between entries. Sometimes
>simple and stupid is good.
>
>                 Linus

-- 
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