[PATCH 2/2] gas model: replace Redlich-Kwong with least-square quintic

Lubomir I. Ivanov neolit123 at gmail.com
Wed Mar 2 17:17:06 PST 2016

On 3 March 2016 at 02:51, Linus Torvalds <torvalds at linux-foundation.org> wrote:
> On Wed, Mar 2, 2016 at 4:24 PM, Linus Torvalds
> <torvalds at linux-foundation.org> wrote:
>> I'll post a test-patch soon, working on it right now.
> Ok, suggested patch posted. It does the linear mixing, *except* for
> the case of actual air. I'd rather use the real air table than trust
> my linear mixing model.
> It has some funny - but believable - effects.
> I see 80(77)cuft for air in an AL80 as expected.
> And now with that gasmix approximation thing, I see 80(78)cuft when I
> have a 32% nitrox mix.
> And the reason I say that is believable, is that it actually sounds
> very reasonable. Oxygen seems to compress *better* than an ideal gas
> (and much better than Nitrogen), and a pure oxygen mix would be 80(84)
> because the compression factor at 3000psi is actually 5% lower volume
> than an ideal gas according to baue. So a higher oxygen content would
> be expected to compress better.
> NOTE! I did not use your new air coefficients, I used our old ones
> from Wikipedia rather than replacing them with your new ones that were
> based on the table at http://www.baue.org/library/zfactor_table.php
> It would be interesting to see a plot of
>  (a) the wikipedia coefficients that we use
>  (b) the coefficients for air you calculated from the air table on baue.org

attached is the comparison of the wiki and baue values for air.
seem pretty close given the possibility of error when measuring.

>  (c) the linear 21/79% mix of the O2/N2 (that we don't actually use,
> since I decided to keep air special, partly because I trust that table
> more, but partly because we just have a special fractional
> representation of air anyway)

i can try that tomorrow, should the linear mix be compared to the AIR
values and if so to which of the tables (baue vs wiki)?

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