<html><head></head><body>It may be overkill, but if going far enough to find a regression equation, should the specific gas mix be taken into account?<br>
<br>
Please note that I have no idea if this table is correct or not for any of the listed gasses: <a href="http://www.baue.org/library/zfactor_table.php">http://www.baue.org/library/zfactor_table.php</a><br><br><div class="gmail_quote">On February 24, 2016 2:18:42 AM EST, Linus Torvalds <torvalds@linux-foundation.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<pre class="k9mail">On Feb 23, 2016 15:46, "Linus Torvalds" <torvalds@linux-foundation.org> wrote:<br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #729fcf; padding-left: 1ex;"><br /></blockquote><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #729fcf; padding-left: 1ex;"> (b) air is not actually entirely compressible.<br /><br /> This is a fairly small factor at 3000psi, but it's a factor.<br /> HOWEVER. The rule for cylinder sizing is that the stated cylinder size<br /> is basically the "theoretical" size, not the real size.<br /></blockquote><br />Actually, doing the math, the compressibility of air is enough to<br />bring that 80 cuft down to about 78 cuft. So that may actually be the<br />biggest effect.<br /><br />We currently approximate the gas volume as being linear below 200 bar,<br />and eat that up-to-3% error.<br /><br />Maybe we could do better.<br /><br />Does
somebody have curve fitting software to generate a better<br />function for the air compressibility factor? From Wikipedia (staying<br />at 300K, which is warm water), we have<br /><br /> bar compressibility<br /> --- ---------------<br /> 1 0.9999<br /> 5 0.9987<br /> 10 0.9974<br /> 20 0.9950<br /> 40 0.9917<br /> 60 0.9901<br /> 80 0.9903<br /> 100 0.9930<br /> 150 1.0074<br /> 200 1.0326<br /> 250 1.0669<br /> 300 1.1089<br /> 400 1.2073<br /> 500 1.3163<br /><br />and we could probably do better than our current "linear plus<br />second-order" approximation.<br /><br />Somebody with R (or matlab) could probably get a reasonable curve from<br />the above data. With a function for the compressibility factor, we<br />could improve on our current "gas_volume()" function.<br /><br />Of course, we could also just do it the stupid way and do the above<br />table and just do linear interpolation in
between entries. Sometimes<br />simple and stupid is good.<br /><br /> Linus<br /></pre></blockquote></div><br>
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