# Floating a helium balloon.

sonhouse
Posers and Puzzles 02 Oct '11 23:34
1. sonhouse
Fast and Curious
02 Oct '11 23:34
So I have played with helium balloons and found a critical weight to dangle underneath so the balloon floats at one height above ground, say 2 meters in the air and stays pretty much at that height, drifting with air movements but more or less balanced in midair.

So you have a balloon that weighs 2 grams and can be blown up to 20 cm in diameter.

So without hanging weights on the balloon to keep it at one altitude, what would be the ratio of He to say Nitrogen, some mixture would do the job just as well as adding weights but how much of He and Nitrogen?
2. talzamir
Art, not a Toil
03 Oct '11 17:29
At zero degrees C temperature, 101 kPa pressure the density of the gasses is
* Helium: 0.1786 g/L
* Nitrogen: 1.251 g/L
* Oxygen: 1.429 g/L

It would be tempting to simply calculate the density of air (4 x 1.251 + 1.529) / 5 and the density of the mixture as some weighed average of the densities of Helium and Nitrogen, set the share of helium as variable, multiply by gravity constant and volume and find the right density for which the lift equals the weight of the balloon rubber. That would give a value, but it would ignore that the rubber stretches as the gas is pumped into the balloon, and therefore the pressure inside the balloon is higher than outside it, which means that more helium is needed in the mixture.

So one more piece of data is needed. Such as the mass of the weight needed to attain equilibrium while using helium only.
3. forkedknight
Defend the Universe
03 Oct '11 20:18
Not all balloons require a pressure difference between inside and outside.

Imagine a balloon made of a non-elastic plastic where the internal and external pressure is at equilibrium.
4. talzamir
Art, not a Toil
04 Oct '11 09:18
Like a sphere made of foil? In that case,

about 2:3 He : N unless I messed up somewhere along the way.
5. 05 Oct '11 14:17
Originally posted by sonhouse
So without hanging weights on the balloon to keep it at one altitude, what would be the ratio of He to say Nitrogen, some mixture would do the job just as well as adding weights but how much of He and Nitrogen?
As an aside to the answers you already have, I'd like to note that the exact amount varies with the air pressure in your room, and therefore with your position on or above (or in my case, below!) sea level, and on a day to day basis, with the weather.

Richard
6. sonhouse
Fast and Curious
15 Oct '11 21:06
Originally posted by Shallow Blue
As an aside to the answers you already have, I'd like to note that the exact amount varies with the air pressure in your room, and therefore with your position on or above (or in my case, below!) sea level, and on a day to day basis, with the weather.

Richard
Yea, I already found that out playing with adding small weights to a regular helium balloon. It is only marginally static. The air in the room is moving by convection a little bit and the temperature differential between the floor and ceiling changes things too.

For instance, I was able to take a balloon and get it to stay mostly in one place, but I could hit it with some energy from an IR lamp and that would heat up the balloon a bit and it would start to rise till it shed the heat and came back to room temp, then it would fall down to where it was. That was a fun experiment.

I imagined a helium balloon with phosphor coatings where it floats around and some IR lasers hit it, say from three sides, with a wide beam as wide as the balloon, and the phosphor reacts to IR to produce visible light, it could be a floating light source with no visible energy source! I know there are IR phosphors because we use them in the photonics industry to be able to visualize where an IR laser beam was, used for collimation of ion implant beamlines where focusing magnets and such have to be accurately placed around the ion beam so it focuses magnetically, if the beam is off center it gets into a shape that makes for non-uniformity doing its dopant thing on silicon wafers. The sensor is a business sized card with a phosphor coating that allows you to see where the beam is, it lights up when hit with IR.