[Enthalpy]

Helium is a limited resource, with shortcomings and high prices in sight.

One of its big uses is to cool apparatus, but helium is too expensive and valuable for this use. The alternative is to use an active, closed-loop cooler.

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There I describe one - sorry for the mess, a cooler wasn't the primary goal of the described hardware:
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051
beginning at the drawings may be easier... And the thread doesn't follow a straight begin-to-end logic, apologies.

In the case of this gas expansion cooler, we have, starting after the cold plate:

• A heat exchanger. Takes cold from the gas here;
• A centrifugal compressor;
• A heat dump, to the atmosphere, to space vacuum, to the next cooling stage...
• The other side of the heat exchanger. Gives cold to the gas;
• A turbine. Cools the gas better than a nozzle, as it extracts work.

Other cycles are described in the linked thread, they correspond to a thermal engine instead of a cooler. Same hardware, different cycle.

The compressor and the turbine are on one shaft with a fast electric motor and magnetic bearings; high speed makes a compact aggregate, drawing:
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051#p23468

The efficient heat exchanger is made of electrodeposited nickel, allowing fast and reliable production of the many thin pipes. Description:
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051#p23419 and
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051&start=20#p26099 and
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051&start=40#p28758

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I give examples for several coolers at different temperatures; 2K would need three steps:
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051&start=20#p26026 gaseous helium between 20K and 300K, to keep hydrogen indefinitely liquid in space
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051&start=20#p26028 gaseous neon between 70K and 300K, to keep methane and oxygen liquid (rocket propellants in space), or nitrogen (Earth)
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051&start=20#p26098 gaseous helium between 2K and 6K
The step between 6K and 20K isn't described, as it's easily extrapolated.

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The primary goal was to produce electricity from heat obtained either by a Solar concentrator (space, Earth) or from radionuclides.
From Sunlight, the converter is more efficient than Solar cells, providing good power even up to Saturn and Uranus http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051&start=20#p23867
As a radioisotopic generator, its efficiency saves much plutonium, as compared to thermoelectric converters and to Stirling.

As a cooler, it enables to store the more efficient oxygen-methane propellants in space for years, even around Venus. Better: even hydrogen can be stored indefinitely. Saves a huge mass in Earth-Moon-Earth and Earth-Mars-Earth scenarios, as well as orbiting Uranus, Neptune...

At 2K, it keeps space cameras and detectors cold indefinitely. The 100M€ space probes can work beyond 2 years, a sad limit of their helium stock up to now.

On Earth, the same technology can produce Solar electricity, but competes with liquid-gas cycles.

A big use on Earth is to store cryogenic gases for long, and replace helium and nitrogen to produce cold.

We might even build fridges and air conditioners with such hardware, maybe without the regenerative heat exchanger. Huge market.

Some pieces of technology have separate uses, like the rotating aggregate which can be an auxiliary power unit on aeroplanes, or the heat exchanger.

Looks like one technological investment can have many uses.
Marc Schaefer, aka Enthalpy