3 ms·
Hot air is lighter than air, and aerogel like low density materials have some weird property where the thermal conductance is lower than bare gas when the mean
by VLM 10y ago
Hot air is lighter than air, and aerogel like low density materials have some weird property where the thermal conductance is lower than bare gas when the mean free path in the aerogel is shorter than the mean free path in bulk gas. In other words they're better hot air balloons than actual hot air balloons.
Something interesting to think about is if they don't leak heat energy very well, and the exterior is something heat proof (steel foil?) you can heat up the air inside to arbitrary temps until radiative glow exceeds the other thermal losses. So if you think nylon hot air balloons are high performance, imagine balloons with much higher lift per volume. A liter of air weighs about a gram so its always going to take a large piece of aerogel to lift me (I weigh quite a few grams) but ...
A hot air balloon sized piece of aerogel is not economically viable right now, even for the military... or is it?
- lgats 10y agoFrom the YouTube videos I've seen, aerogel doesn't quite float when it's heated up. Interesting theory though if a similar substance is discovered.
- knodi123 10y agoLow-density materials surrounded by a thin shell are still going to weight a lot more than air surrounded by a thin shell. Also, you have to look into how this is going to be heated. For a hot air balloon to work, all the air inside has to be hot. If your balloon is filled with an amazingly efficient insulator.... Also, the reason airships use lighter-than-air gas is because then they don't have to carry lots of heavy fuel for heating air. Things like fuel, and pipes to carry heat throughout your aerogel, will rapidly eat up any efficiencies you gained.