Airbus pioneers a superconducting powertrain cooled by liquid hydrogen • Hacker News Board

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#11

Post by ethbr0 » Wed, Apr 21, 2021, 1:47 PM UTC

ncmncm wrote: post #9

intrepidhero wrote: post #2

This makes no sense to me. Don't you also need cryogenic systems to keep the H2 cold? Wouldn't those use waaaaay more energy than what you save with superconducting motors? Maybe they are talking about short haul flights where the H2 is ground cooled and then used as a cold sink but then in order to keep your electronics cold you're carrying lots more fuel than you need. TFA was too thin to pass the sniff test.

The idea is that a large-scale LH2 flow into the system is being consumed, and perforce heated, and may be used as refrigerant on the way there. It makes perfect sense. Rockets do this today, as indeed they have done from the earliest days, sending liquified gases through channels in the engine bell and combustion chamber before burning, keeping them both from vaporizing. Here, the very high efficiency of electric-dr…

Aka regenerative cooling: https://en.m.wikipedia.org/wiki/Regenerative_cooling_(rocket...

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#12

Post by Tuna-Fish » Wed, Apr 21, 2021, 1:49 PM UTC

intrepidhero wrote: post #2

This makes no sense to me. Don't you also need cryogenic systems to keep the H2 cold? Wouldn't those use waaaaay more energy than what you save with superconducting motors? Maybe they are talking about short haul flights where the H2 is ground cooled and then used as a cold sink but then in order to keep your electronics cold you're carrying lots more fuel than you need. TFA was too thin to pass the sniff test.

This is effectively regenerative cooling, like what rockets are commonly using. There are no cryogenic systems onboard, but all the fuel is loaded as very cold, and you can use the fuel as a coolant just before you burn it.

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#13

Post by ethbr0 » Wed, Apr 21, 2021, 1:51 PM UTC

XorNot wrote: post #5

intrepidhero wrote: post #2

This makes no sense to me. Don't you also need cryogenic systems to keep the H2 cold? Wouldn't those use waaaaay more energy than what you save with superconducting motors? Maybe they are talking about short haul flights where the H2 is ground cooled and then used as a cold sink but then in order to keep your electronics cold you're carrying lots more fuel than you need. TFA was too thin to pass the sniff test.

Motors are solid 3D structures. The more power you put in not superconducting, the more heat you have to extract. Superconductors mean you only need to keep your refrigerant cool, and that's a product of insulation effectiveness, not power output.

This is the difference between electric and combustion powertrains, no?

In electric, heat is the enemy and inefficient.

In combustion, heat is a key component of the thermodynamic efficiency, unavoidable, and effectively only limited by material tolerances.

(I didn't major in physics, so someone keep me honest on the ceiling / floor efficiency equations for combustion engines?)

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#14

Post by ncmncm » Wed, Apr 21, 2021, 1:51 PM UTC

throwaway0a5e wrote: post #10

ncmncm wrote: post #8

Earlier quoted context omitted.

[superseded]

Yeah, people don't like being told they fell for exactly what the editor who chose the title wanted them to fall for.

No, ignorant editorial bloviating is specifically forbidden in the ToS.

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#15

Post by redis_mlc » Wed, Apr 21, 2021, 1:54 PM UTC

The aviation industry is exploring alternative fuels in case of draconian regulation, including sustainable aviation fuel (SFA) and hydrogen.

But the problems with hydrogen as an aviation fuel are many:

- hydrogen embrittlement of containers

- volatility (compared to Jet A). Since hydrogen is the smallest molecule, it can escape any container.

- distribution (world-wide locations and airport safety)

- containment weight and condensation

- containment integrity at low temperatures (airplanes flex and fuselage fasteners fail around 33,000 cycles.)

And ffs, the Hindenburg:

https://en.wikipedia.org/wiki/Hindenburg_disaster

https://www.avweb.com/ownership/fuel-news/williams-internati...

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#16

Post by upofadown » Wed, Apr 21, 2021, 1:55 PM UTC

intrepidhero wrote: post #2

This makes no sense to me. Don't you also need cryogenic systems to keep the H2 cold? Wouldn't those use waaaaay more energy than what you save with superconducting motors? Maybe they are talking about short haul flights where the H2 is ground cooled and then used as a cold sink but then in order to keep your electronics cold you're carrying lots more fuel than you need. TFA was too thin to pass the sniff test.

The H2 keeps itself cold by boiling away. You just need some insulation to slow down the rate to something manageable. Insulation normally uses a gas such as air to block the heat flow and as a result tends to be very light.

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#17

Post by Tuna-Fish » Wed, Apr 21, 2021, 1:57 PM UTC

ncmncm wrote: post #4

I have estimated that an Airbus A320 generates something on the order of 80 MW during takeoff. A hydrogen-powered aircraft, for the same freight load, will have benefit of efficiencies not available to an A320, so the needed power will be less, but I don't know how much less. The 0.5 MW system described looks like a good first step, but should be scaled up quickly. Results will be immediately useful for co-generation…

If I understand correctly, this makes use of a hydrogen fuel cell for electric power, and then has that turn electric fans.

In general, a modern fuel cell is ~60% efficient at turning chemical energy into electricity, and an electric fan is ~4x as efficient at turning electricity into thrust when compared to a turbofan engine turning chemical energy into thrust.

So ignoring transmissions losses (which would probably be really low anyway if ran on superconductors...) you'd need about 40% of the power of a modern jet to do the same work. There is clearly a lot of scaling work needed, and I don't see a fuel cell/electric aircraft beating existing ones anytime soon if you ignore the emissions, but at least this clearly shows that there is a future for mass commercial aviation once burning carbohydrates is no longer acceptable.

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#18

Post by upofadown » Wed, Apr 21, 2021, 2:04 PM UTC

userbinator wrote: post #6

The failure modes are going to be interesting, to say the least...

Yeah, It would be great if any fires were to burn clean and had a strong tendency to rise away from the aircraft, particularly for ground fires. H2 is also nice in that it doesn't create a lot of infrared energy while it burns.

You might be able to save the weight of any fire suppression systems.

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#19

Post by petertodd » Wed, Apr 21, 2021, 2:13 PM UTC

intrepidhero wrote: post #2

This makes no sense to me. Don't you also need cryogenic systems to keep the H2 cold? Wouldn't those use waaaaay more energy than what you save with superconducting motors? Maybe they are talking about short haul flights where the H2 is ground cooled and then used as a cold sink but then in order to keep your electronics cold you're carrying lots more fuel than you need. TFA was too thin to pass the sniff test.

> Don't you also need cryogenic systems to keep the H2 cold? Wouldn't those use waaaaay more energy than what you save with superconducting motors?

Probably not. Cryogenic liquids like liquid H2 are typically stored in dewers, which use a vacuum as the primary insulation, along with silvered surfaces and layers of mylar film to reduce radiation losses. We've been able to make dewers with boil off rates of 1% per day or better for decades. That's more than low enough that you don't need any refrigeration at all for an aircraft application where the flight just lasts a few hours anyway.

Most likely they'll actually use less effective insulation to save weight. Fortunately for them, cryogenic liquids are commonly used in rockets, so there's already lots of know-how and technology out there for making lightweight cryogenic insulation.

Re: Airbus pioneers a superconducting powertrain cooled by liquid hydrogen

#20

Post by XorNot » Wed, Apr 21, 2021, 2:22 PM UTC

ethbr0 wrote: post #13

XorNot wrote: post #5

Earlier quoted context omitted.

Motors are solid 3D structures. The more power you put in not superconducting, the more heat you have to extract. Superconductors mean you only need to keep your refrigerant cool, and that's a product of insulation effectiveness, not power output.

This is the difference between electric and combustion powertrains, no? In electric, heat is the enemy and inefficient. In combustion, heat is a key component of the thermodynamic efficiency, unavoidable, and effectively only limited by material tolerances. (I didn't major in physics, so someone keep me honest on the ceiling / floor efficiency equations for combustion engines?)

You still have to cool a combustion engine - hence why car's have radiators.

Combustion engine's are also limited by Carnot cycle engine efficiency - about 64% theoretically, no more then 50% in the real world. So you're still going to wind up having to dump progressively more heat from a fixed surface area.