blacknet
Contributor
Scuba_Vixen,
So what % for O2 and Air?
Ed
So what % for O2 and Air?
Ed
Gas Blending Math (He and Nitrox)
- Thread starter Raywerner
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Scuba_Vixen
Guest
They vary with gas percentage and pressures. Take a look at this spreadsheet as you plug in different mixes and see the change in z-factors and the percentage change they represent in the amount of gas to add or subtract from ideal.
http://www.atomox.com/documents/real_gas.xls
There's a pdf format page that has all the equations if you want to incorporate them into your program.
An interesting way to see the interplay of the z-factors is to see the values for heliox mixes, use the same mix at different pressures (like 2000# and again at 3200#...as if you made it without a booster and then with)
Then look at something like 18/35 and then 10/70 (both at 3200# or so, which is a normal fill range), again you'll see more change as a higher percentage of the mix is a more compressable gas.
Hope that helps,
Darlene
http://www.atomox.com/documents/real_gas.xls
There's a pdf format page that has all the equations if you want to incorporate them into your program.
An interesting way to see the interplay of the z-factors is to see the values for heliox mixes, use the same mix at different pressures (like 2000# and again at 3200#...as if you made it without a booster and then with)
Then look at something like 18/35 and then 10/70 (both at 3200# or so, which is a normal fill range), again you'll see more change as a higher percentage of the mix is a more compressable gas.
Hope that helps,
Darlene
blacknet
Contributor
Hello,
I have used the the table on that site but would like to use the formula. The only problem I see is there are way to many variables that comes into play with the Z factor. I have talked to many blenders and everyone tells me they use +5% for He and use the idea number of O2 and top with air. Said their typical mixes of He falls between 40-60%, which is 1200 and 1800 psi. according to the chart that is in the 5% range.
What would be good is to use a basic Beattie-Bridgeman equasion instead of the chart.
Ed
I have used the the table on that site but would like to use the formula. The only problem I see is there are way to many variables that comes into play with the Z factor. I have talked to many blenders and everyone tells me they use +5% for He and use the idea number of O2 and top with air. Said their typical mixes of He falls between 40-60%, which is 1200 and 1800 psi. according to the chart that is in the 5% range.
What would be good is to use a basic Beattie-Bridgeman equasion instead of the chart.
Ed
If you take a couple days to mix it works well to use real gas laws. However if you're not going to take the time to let things ccol and the re-top temperature has a greater effect than compressability. In that case you do better by guessing and just adding a little extra He and maybe a little less O2.
My wife takes two days to mix and uses the Atomox spread sheet. I just dump in the gas, analyze and dive.
My wife takes two days to mix and uses the Atomox spread sheet. I just dump in the gas, analyze and dive.
Scuba_Vixen
Guest
isn't going to be a major factor in the first mix or maybe two, By the time you get to the 5th or 6th fill without dumping and starting fresh, The accrued error can get to be significant, if you're not being as accurate as possible with each fill. If you live where He prices are reasonable, dumping every 2 to 3 fills is easy. At almost $200 a bottle, I try to use it efficiently. (though I believe saving money by using lower % is false economy).
All in all, 5% as a rule of thumb, probably accounts well for compressability and heating. It's just that some of us anal retentive engineering types have too many thumbs.
Darlene
All in all, 5% as a rule of thumb, probably accounts well for compressability and heating. It's just that some of us anal retentive engineering types have too many thumbs.
Darlene
The Beattie-Bridgeman equation is a complicated fit to experimental data. It requires 5 specific parameter values in addition to the critical point values for each gas. The B-B is not a trivial matter to implement. A typical learning exercise for upper level Chem-E majors is to write a FORTRAN program that will calculate the Z for a selected gas at a specific temperature. Most dont get it right.
The individual behavior of the gas is dependent upon the molecule size and its attractive forces. The Atomox spread sheet is a good general guide on the real gas behavior for high pressure and small (relative) volume interactions. More detailed specific needs go beyond typical scuba applications.
An important additional factor to consider when mixing is the accuracy of your gauges. It does not take long to for the errors to multiply.
omar
The individual behavior of the gas is dependent upon the molecule size and its attractive forces. The Atomox spread sheet is a good general guide on the real gas behavior for high pressure and small (relative) volume interactions. More detailed specific needs go beyond typical scuba applications.
An important additional factor to consider when mixing is the accuracy of your gauges. It does not take long to for the errors to multiply.
omar
blacknet
Contributor
Hello,
You are correct that it's not an easy process. I have been consulting my thermodynamics book on this and i'm not sure if it's worth investing the time and energy. For most blenders they use 40%-60%ish of He and o2 is close to 1 it's probably not worthwhile adding anything extra in.
Ed
You are correct that it's not an easy process. I have been consulting my thermodynamics book on this and i'm not sure if it's worth investing the time and energy. For most blenders they use 40%-60%ish of He and o2 is close to 1 it's probably not worthwhile adding anything extra in.
Ed
blacknet
Contributor
Hello,
I just added a zfactor lookup. The metric conversion is still abit on the buggy side but the imperial works great.
Ed
Your blender program file is huge! It would take me a loooong time to download on a dialup. How is it different than the Atomox blender... other than the later's compact size since it is an excel file?
blacknet
Contributor
Hello,
The PC version which is rolled all inclusive install package is 11 megs, that includes MDAC 2.6. If you already have mdac then you can just get the exe which is 164k. The exe is at http://wetlands.simplyaquatics.com/software/blender-PC.exe
I'm not familar with the Atomox package. Mine does zfactor (still working on some bugs with this), cost of gas, metric/imperial (tho the metric has some slight issues) hypoxic, max end, po2, ead, mod@1.6 and 1.4, best mix @1.6 and 1.4, blowoff, tank stats and bank mix top off.
Ed
The PC version which is rolled all inclusive install package is 11 megs, that includes MDAC 2.6. If you already have mdac then you can just get the exe which is 164k. The exe is at http://wetlands.simplyaquatics.com/software/blender-PC.exe
I'm not familar with the Atomox package. Mine does zfactor (still working on some bugs with this), cost of gas, metric/imperial (tho the metric has some slight issues) hypoxic, max end, po2, ead, mod@1.6 and 1.4, best mix @1.6 and 1.4, blowoff, tank stats and bank mix top off.
Ed
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