# Do liquid hydrogen-based cooling devices exist and what are they used for?

Liquid hydrogen cooling could be some intermediate solution between helium and liquid nitrogen based cooling. For example, some type of superconductors could be cooled by liquid H2, and this could be much cheaper than the liquid He.

What are their most characteristic applications in the industry?

• @Sklivvz I am sorry if I didn't formulated enough well. What about this: youtube.com/watch?v=2I12wkGrvts ? – peterh - Reinstate Monica Jan 20 '15 at 22:22
• @PeterHorvath Hydrogen gas forms an explosive mix with air. Then again, the watermark on that video is says StupidVideos.com – Nick Alexeev Jan 20 '15 at 22:27
• @NickAlexeev People can buy liquid hidrogen. A considerable part of the green cars are going with liquid h2. Is it really nonexisting? I think, for example, for cooling superconducting materials, it could been much cheaper as the liquid helium. – peterh - Reinstate Monica Jan 20 '15 at 22:32

The combustion chamber and nozzle of the Space Shuttle main engine were cooled with liquid hydrogen. Liquid hydrogen was also the fuel. It was used as a coolant before it was burned (regenerative cooling).

Another example is the air breathing rocket engine SABRE. Here too liquid hydrogen is used as fuel. It's also used for liquefying the atmospheric oxygen.

In the industry, one advantage that liquid helium and nitrogen have over hydrogen is that helium and nitrogen are inert and non-combustible. Probably less corrosive too.

p.s. The question has a tag. So, I don't know if this is the sort of application of liquid hydrogen cooling that the O.P. is looking for.

• I suspected, the answers will come mainly from the superconducting line, but surprisingly, not. Thank you the answer! – peterh - Reinstate Monica Jan 20 '15 at 22:39

Gaseous hydrogen is often used to cool the large generators in power plants. "Hydrogen’s low gas density, high specific heat, and high thermal conductivity" are listed in the GE link as the major drivers behind its use.

For instance:

http://en.wikipedia.org/wiki/Hydrogen-cooled_turbo_generator

https://powergen.gepower.com/plan-build/products/generators/hydrogen-cooled.html

On the matter of explosions - hydrogen is not particularly explosive without oxygen present. The goal, then, is to provide a system that keeps the hydrogen free from impurities (air) by sealing it off from the outside air. The purity of the hydrogen in the system is constantly monitored, and in an emergency the gas is evacuated by CO2. It's also worth noting that while helium is not explosive and very similar to H2 physically, it is too expensive to use as a cooling medium.

• A question mark on helium being "very similar to H2 chemically"... – Flyto Feb 3 '15 at 8:37
• Yes, this is a huge generalization. Suggestions for a rewording? Helium is a major competitor for H2, namely because it shares the "low gas density, high specific heat, and high thermal conductivity" properties cited by GE. I'm not a ChemE, so I have trouble going into any further depth than that. – KTM Feb 3 '15 at 12:40
• That sounds to me as though He and H2 are similar in their physical properties, rather than their chemical ones. Or, to be clearer, you could just say "offers similar properties to H2 such as low density, high specific heat, and high thermal conductivity" :-) – Flyto Feb 3 '15 at 12:47
• (that they are very different chemically can be easily demonstrated with some air and a match... :-)) – Flyto Feb 3 '15 at 12:47
• H2 is very similar to He physically, very different chemically (far worse for most goals because it is a huge explosion hazard), and much better economically (\$). Thus, their actual selection is determined by that is the explosion hazard acceptable for the much lower price. Note also, He has a limited availability, a side product of oil refinery, if we have more energy, we can't have more helium. If we need more helium, its price will grow but we won't have more. If we need more H2, then we simply extract more by water electrolysis and its price won't grow (may even decrease). – peterh - Reinstate Monica Nov 16 '18 at 11:40