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

[Lubomir I. Ivanov]

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)?

lubomir
--
-------------- next part --------------
A non-text attachment was scrubbed...
Name: z_air_wiki_vs_baue.png
Type: image/png
Size: 17495 bytes
Desc: not available
URL: <http://lists.subsurface-divelog.org/pipermail/subsurface/attachments/20160303/97f97c37/attachment-0001.png>