Atmospheric pressure hydrogen storage experiments
Posted: Sat Dec 17, 2016 6:56 pm
Rex and I have expressed interest in mylar balloons for temporary storage of deuterium.
The topic came up in one marginally related forum thread recently: viewtopic.php?f=6&t=9435&start=20#p73876
For what it's worth, I just measured an air-filled, sealed mylar balloon. It had gathered dust for months, along with my PEM cell kits. In that other thread I mentioned the "mylar balloon" geometric shape. It maximizes the volume for a given generatrix length, the amount of unstretchy film along a "meridian" from pole to equator.
Anyway, this specimen appears to be a nominal 9 inch balloon. Diameter of flat circle before inflation, including the seam allowance. As found today, the puffy shape has OD of about 6.5 inches and thickness of about 4 inches.
Volume is about 1.7 liters. Measured by water displacement in a plastic nursery pot, since one was handy with no holes at the bottom. Two different ways. Archimedes would surely be pleased.
1) Change in apparent weight of the partly filled pail, when floating balloon was pushed down until submerged. (White colander-like object was used to spread out the pushing down force, but same result was obtained just pushing with fingers.) As expected, the answer was practically independent of the amount of water and the depth of submersion.
2) Mark the waterline when inflated balloon is submerged, then remove balloon and measure the water to refill pail to same level.
Empirically, the volume is about 27% of that of a sphere with same nominal diameter. Also about 1.14 times the cube of nominal radius, and about 5% greater than the volume of a sphere with the same axial circumference. Anyone want to compare those with the closed-form solution given in Wikipedia?
I bet it would be against rules to send a balloon full of deuterium by U. S. mail, or to take it on board an airplane. The latter might be done more or less overtly, by pretending that the buoyant balloon contained helium. But if you got caught, it would be a topic for national news. Especially if you aren't white! Last time the topic came up, we joked about large parcels with gross weight near zero because of helium or deuterium balloons. Enough hydrogen to fill the small balloon pictured above would have about the same fuel mass as one wooden match.
The topic came up in one marginally related forum thread recently: viewtopic.php?f=6&t=9435&start=20#p73876
For what it's worth, I just measured an air-filled, sealed mylar balloon. It had gathered dust for months, along with my PEM cell kits. In that other thread I mentioned the "mylar balloon" geometric shape. It maximizes the volume for a given generatrix length, the amount of unstretchy film along a "meridian" from pole to equator.
Anyway, this specimen appears to be a nominal 9 inch balloon. Diameter of flat circle before inflation, including the seam allowance. As found today, the puffy shape has OD of about 6.5 inches and thickness of about 4 inches.
Volume is about 1.7 liters. Measured by water displacement in a plastic nursery pot, since one was handy with no holes at the bottom. Two different ways. Archimedes would surely be pleased.
1) Change in apparent weight of the partly filled pail, when floating balloon was pushed down until submerged. (White colander-like object was used to spread out the pushing down force, but same result was obtained just pushing with fingers.) As expected, the answer was practically independent of the amount of water and the depth of submersion.
2) Mark the waterline when inflated balloon is submerged, then remove balloon and measure the water to refill pail to same level.
Empirically, the volume is about 27% of that of a sphere with same nominal diameter. Also about 1.14 times the cube of nominal radius, and about 5% greater than the volume of a sphere with the same axial circumference. Anyone want to compare those with the closed-form solution given in Wikipedia?
I bet it would be against rules to send a balloon full of deuterium by U. S. mail, or to take it on board an airplane. The latter might be done more or less overtly, by pretending that the buoyant balloon contained helium. But if you got caught, it would be a topic for national news. Especially if you aren't white! Last time the topic came up, we joked about large parcels with gross weight near zero because of helium or deuterium balloons. Enough hydrogen to fill the small balloon pictured above would have about the same fuel mass as one wooden match.