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General Science => General Science => Topic started by: BRTYERY on 19/09/2018 07:27:13

Title: What can go higher, a hydrogen-filled balloon, or a hot air balloon?
Post by: BRTYERY on 19/09/2018 07:27:13
Hello

What can achieve a greater height, a hydrogen-filled balloon, or a hot air balloon?
Title: Re: What can go higher, a hydrogen-filled balloon, or a hot air balloon?
Post by: BRTYERY on 19/09/2018 07:30:42
Hello
this both vs
Title: Re: What can go higher, a hydrogen-filled balloon, or a hot air balloon?
Post by: chris on 23/09/2018 10:46:37
Both work by the same principle: a less-dense fluid displaces a greater mass of a more dense fluid so it feels a buoyancy force upwards.

Therefore, neglecting engineering and other constraints, both have the potential to reach similar altitudes.

BUT - since a hot-air balloon relies upon hot air to rise, and the source of that hot air is usually propane combusted in air, in the thinner air at altitude there would be much less oxygen and therefore the supply of oxidant would be lower, limiting the thermal output of the fuel and hence the ability of the balloon to rise further.

The helium balloon faces a different challenge: the balloon will feel less air pressure as it rises, making the balloon expand. The material used for the construction therefore needs to be able to accommodate such an expansion, otherwise it will burst.

Does everyone agree?
Title: Re: What can go higher, a hydrogen-filled balloon, or a hot air balloon?
Post by: evan_au on 23/09/2018 11:01:54
What's the matter with a hot-hydrogen balloon?
...apart from the fact that you wouldn't use it to carry passengers!
...the Hindenberg seared too many graphic images into people's brains...

See: https://en.wikipedia.org/wiki/Rozi%C3%A8re_balloon
Title: Re: What can go higher, a hydrogen-filled balloon, or a hot air balloon?
Post by: guest45734 on 23/09/2018 11:16:57
BUT - since a hot-air balloon relies upon hot air to rise, and the source of that hot air is usually propane combusted in air, in the thinner air at altitude there would be much less oxygen and therefore the supply of oxidant would be lower, limiting the thermal output of the fuel and hence the ability of the balloon to rise further.

Rather than using a conventional burner, why not use liquid oxygen and hydrogen to heat the gas. Maybe that would enable it to rocket of the ground. :)

Using a bit of google https://www.sciencefocus.com/science/how-high-can-a-helium-balloon-float/
"Watching them fly off up into the sky, there seems no limit to how high a helium balloon can go. In reality, there are two major constraints: the strength of the balloon material, and Archimedesís principle. As a balloon ascends, the pressure of the surrounding air drops while the helium inside expands. Toy balloons burst at around 10km, while professional meteorological balloons reach heights of 30km.

The ultimate limit is set by Archimedesís Principle, which says balloons will stop rising once their density matches the surrounding air. So thereís no chance of balloons entering the vacuum of space. However, in 2002, a helium balloon built by Dr Takamasa Yamagami and colleagues at the Institute of Space and Astronautical Science climbed to 53km Ė half way to the official edge of space."