3 ms·

I'd been wondering if an aerogel sphere with a mylar coating (constructed under vacuum) would be sufficiently low density to float - the aerogel would let it re

I'd been wondering if an aerogel sphere with a mylar coating (constructed under vacuum) would be sufficiently low density to float - the aerogel would let it resist the pressure and the mylar would seal it. I guess the aerogel would be dense enough compared to hydrogen that a conventional balloon would be better in all respects though. Still curious as to whether it's been done already though.

Scalene2 3y ago
Making an aerogel sphere in a vacuum would be quite the challenge.
- dcminter 3y ago
  I mean you need a vacuum to create an aerogel in the first place!
dsign 3y ago
I have done a bit of research on that. I don’t think that current aerogels are engineered to withstand full atmospheric pressure. With that said, the approach would make sense for a number of reasons: - Helium and hydrogen “escape from everywhere”. - Hydrogen burns - Helium is obtained from natural gas and is rather expensive. An aerogel made from biomaterials (think of a sort of bio-engineered coral) could possibly have enough strength and low density.
- dcminter 3y ago
  I thought the silica based ones were pretty strong under compression? Edit: Wikipedia has a persuasive picture of some aerogel supporting a house brick!
namibj 3y ago
Water is lighter than air and only needs a modest temperature to have it's vapor pressure exceed ambient pressure at high altitude. Bonus for self-inflating when you reach altitude/letting you accumulate thermal energy in some form and take off by dumping the heat into your liquid water bladder to inflate your water vapor balloon. Wonder how well/cheaply (in weight for $affordable budget) you could insulate the balloon to curb your thermal power demand. Maybe enough that you could use your liquid water bladder with a little insulation as a thermal mass to run an absorption heat pump (Type2: warm power, cold sink, hot target output) off of ambient temperature during the day, cooling the thermal mass back down during the night. Or lightweight solar panels, I suppose, feeding an air-source heat pump to boil the water. Normal Li-ion batteries sadly don't really have enough energy density (water takes 620 Wh/kg to boil; commercial energy-dense Li-ion is in the 200~300 Wh/kg range; at sea level and boiling point (=lowest possible temperature without it wanting to condense on every dust particle and other condensation nucleus) water vapor is half as dense as 20°C air so it could lift itself twice (and once it's used to lift itself already), and even a very good heat pump will have severe difficulty reaching a COP of 4.0). So I guess if you try really hard you could make a self-inflating steam balloon that takes off using Li-ion fed heat pumps and later stays airborne using solar cells to continue feeding the heat pumps...
- dcminter 3y ago
  Did you intend to reply to a different comment? This doesn't have much relevance to mine. Also - "water is lighter than air" is an odd claim.
  - namibj 3y ago
    Yeah, sorry, drifted off towards the end somewhat. But no, water is lighter than air. In it's gaseous form. Which requires substantial temperature or low pressure. The former you can make easily, the latter you encounter if you fly high enough.

Scalene2 3y ago

Making an aerogel sphere in a vacuum would be quite the challenge.

dcminter 3y ago
I mean you need a vacuum to create an aerogel in the first place!

dsign 3y ago

I have done a bit of research on that. I don’t think that current aerogels are engineered to withstand full atmospheric pressure. With that said, the approach would make sense for a number of reasons: - Helium and hydrogen “escape from everywhere”. - Hydrogen burns - Helium is obtained from natural gas and is rather expensive. An aerogel made from biomaterials (think of a sort of bio-engineered coral) could possibly have enough strength and low density.

dcminter 3y ago
I thought the silica based ones were pretty strong under compression? Edit: Wikipedia has a persuasive picture of some aerogel supporting a house brick!

namibj 3y ago

Water is lighter than air and only needs a modest temperature to have it's vapor pressure exceed ambient pressure at high altitude. Bonus for self-inflating when you reach altitude/letting you accumulate thermal energy in some form and take off by dumping the heat into your liquid water bladder to inflate your water vapor balloon. Wonder how well/cheaply (in weight for $affordable budget) you could insulate the balloon to curb your thermal power demand. Maybe enough that you could use your liquid water bladder with a little insulation as a thermal mass to run an absorption heat pump (Type2: warm power, cold sink, hot target output) off of ambient temperature during the day, cooling the thermal mass back down during the night. Or lightweight solar panels, I suppose, feeding an air-source heat pump to boil the water. Normal Li-ion batteries sadly don't really have enough energy density (water takes 620 Wh/kg to boil; commercial energy-dense Li-ion is in the 200~300 Wh/kg range; at sea level and boiling point (=lowest possible temperature without it wanting to condense on every dust particle and other condensation nucleus) water vapor is half as dense as 20°C air so it could lift itself twice (and once it's used to lift itself already), and even a very good heat pump will have severe difficulty reaching a COP of 4.0). So I guess if you try really hard you could make a self-inflating steam balloon that takes off using Li-ion fed heat pumps and later stays airborne using solar cells to continue feeding the heat pumps...

dcminter 3y ago
Did you intend to reply to a different comment? This doesn't have much relevance to mine. Also - "water is lighter than air" is an odd claim.
- namibj 3y ago
  Yeah, sorry, drifted off towards the end somewhat. But no, water is lighter than air. In it's gaseous form. Which requires substantial temperature or low pressure. The former you can make easily, the latter you encounter if you fly high enough.