Ok, so I was blending deco gas yesterday...50% in a 80 and a 40. I filled them at the same time..1106psi of O2 and topped with air. For some reason my 80 analyzed at 50% but my 40 read 44.6%. Any thoughts?
weird fill
- Thread starter tomfcrist
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kwinter
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Just the usual thoughts.
What was in each tank before?
Did you let temperature stabilize before adding the second gas?
How accurate is your pressure gauge?
Are you using ideal gas law numbers or real gas numbers, and which formula?
I'll admit a 5% difference sounds a bit high, but not too much considering different cylinder sizes.
Please pardon any typos. Sent from my iPhone using Tapatalk
What was in each tank before?
Did you let temperature stabilize before adding the second gas?
How accurate is your pressure gauge?
Are you using ideal gas law numbers or real gas numbers, and which formula?
I'll admit a 5% difference sounds a bit high, but not too much considering different cylinder sizes.
Please pardon any typos. Sent from my iPhone using Tapatalk
Not trying to bust balls, but you are asking for a solution to a "scientific" anomaly but have ill-defined variables... what do you mean by "at the same time"? Did you use the same gauge to measure pressures? What was the final pressure in each cylinder? What was your filling rate? how much time between filling and analyzing? What gas flow rate when analyzing? ET AL
My guess would be a combination of tank internal geometry and gas temperature given everything else was the same.
Gas under pressure (let's say in excess of 100 bar) begins to display odd behavior. The internal dimension of the tank and the temperature of its wall will tend to influence the reading you get.
My guess would be a combination of tank internal geometry and gas temperature given everything else was the same.
Gas under pressure (let's say in excess of 100 bar) begins to display odd behavior. The internal dimension of the tank and the temperature of its wall will tend to influence the reading you get.
OP
Both tanks were empty( just did viz ). Let everything cool, using real gas #'s...and I'm stumped. I've never blended in different size cylinders simultaneously, so that may be the issue, but one would think that proportions are proportions. Guess I'll go back to filling my 80's and 40's separately.
I use a digital guage on my fill manifold. Fill rate 200psi/min when topping up, 80psi/min with O2. I waited a good hour before analyzing. My balls are not busted...I appreciate the input.
I use a digital guage on my fill manifold. Fill rate 200psi/min when topping up, 80psi/min with O2. I waited a good hour before analyzing. My balls are not busted...I appreciate the input.
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How do they analyze today? I've had it take 2 days for the gas to mix in a smaller cylinder. I am blessed to be able to bank gas and then decant it.
OP
The smaller tank will heat up a lot more (as it fills faster and has no time to dissipate heat during the fill). When it finally cools down, the pressure drops more.
There is more heating during the initial fill from 1 to 100 bar (100x pressure) than during the topping from 100 to 200 bar (2x ppressure). Because of this, the phenomenon only affects the first fill, not the topping.
Hence, there will be a lower count of oxygen molecules in the smaller tank as a result.
Sometimes 55 is 50.
This phenomenon is not relevant if the tanks don't get hot during the O2 fill.
Did you use the same SPG for both tanks? I seem to have to differently calibrated SPGs. One is calibrated for surface (zero is ~one ATM, surface air) and the other is calibrated for 90 meters/270 ft (zero is ~10 ATM surface air, or ambient pressure at 90m).
______________
ps. The amount of oxygen is not properly described by pressure and temperature but by weight. Weight is independent of pressure and temperature.
There is more heating during the initial fill from 1 to 100 bar (100x pressure) than during the topping from 100 to 200 bar (2x ppressure). Because of this, the phenomenon only affects the first fill, not the topping.
Hence, there will be a lower count of oxygen molecules in the smaller tank as a result.
Sometimes 55 is 50.
This phenomenon is not relevant if the tanks don't get hot during the O2 fill.
Did you use the same SPG for both tanks? I seem to have to differently calibrated SPGs. One is calibrated for surface (zero is ~one ATM, surface air) and the other is calibrated for 90 meters/270 ft (zero is ~10 ATM surface air, or ambient pressure at 90m).
______________
ps. The amount of oxygen is not properly described by pressure and temperature but by weight. Weight is independent of pressure and temperature.
Last edited:
Good observation. Small tanks need a slower fill rate.
How did they compare after a bit more time, mate?
OP
The 40 analyzed at 49 last night. Guess it just took some time.
