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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Lloyd Conquers the VanDerWaals Equation !

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rsterne:
My good friend Lloyd Sikes is a modest man, not prone to seeking the limelight.... He has spent a HUGE amount of time trying to get an Excel spreadsheet to solve the VanDerWaals equation that will work at all (usable for us) temperatures and pressures.... There are several online calculators, but most of them do not give the correct answer at high pressures.... or in one case work perfectly for large volumes (eg. 1 m^3) but not for the smaller volumes we use (1 litre = 0.001 m^3 or less)…. The equation is easy to solve for pressure and temperature.... but not so for volume, or the mass of the gas (n = number of moles)…. both of which need to be solved as cubic equations.... Lloyd refused to give up, and has finally done it, and I, for one am VERY proud of him.... Here is a chart I derived from his spreadsheet, showing how air deviates from an ideal gas at high pressures....



Below about 3300 psi (at 20*C), air is actually slightly more dense than Boyle's Law for Ideal Gasses predicts, and after that it is less dense than the Ideal Gas Laws would calculate.... Below 4000 psi, the difference (plus or minus) is less than 6%, so for most "back of the napkin" calculations, you can use Boyle's Law.... However, as the pressure increases, the effect of the space taken up by the molecules themselves can no longer be ignored, and at 6000 psi air is actually almost 20% less dense than predicted by Boyle's Law.... By the time you get to 10,000 psi, air as a Real Gas is 40% less dense than Boyle says it "should" be.... As the temperature increases, the difference is even greater....

Anyways, I figured Lloyd, in his modest way, wouldn't seek public acknowledgement for this achievement.... It will allow him to revise his Internal Ballistics Spreadsheet to use mass flow, which should increase the accuracy of it significantly....

I'm proud of him, and proud to call him my friend....

Bob

Michael Loar:
I will second that acknowledgment and give a big hip hip hooray for all his endless hard work.

Mike

YEMX:
This is great news!!

A hearty congratulations and THANK YOU to Lloyd!! 

shorty:
Congrats..... :D :D :D :D

Back_Roads:
 Nice work ... Lloyd ! Sometimes I think of Lloyd as a mouse in Bob's shirt pocket next to a slide rule  ???

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