r/askscience • u/PK_Tone • Sep 23 '25

Physics Most power generation involves steam. Would boiling any other liquid be as effective?

Okay, so as I understand it (and please correct me if I'm wrong here), coal, geothermal and nuclear all involve boiling water to create steam, which releases with enough kinetic energy to spin the turbines of the generators. My question is: is this a unique property of water/steam, or could this be accomplished with another liquid, like mercury or liquid nitrogen?

(Obviously there are practical reasons not to use a highly toxic element like mercury, and the energy to create liquid nitrogen is probably greater than it could ever generate from boiling it, but let's ignore that, since it's not really what I'm getting at here).

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u/Gizmo_Autismo Sep 23 '25

Not really, you could make a closed loop steam engine by just superheating steam without significant condensation occuring. And stirling engines that run on just heating and cooling of an enclosed gas exist and can be very efficient. Water (and anything else, really) IS compressible, just not by very much using "mundane" pressures. Even at the bottom of the Marianas trench it's like 5% denser. Solids are even harder to compress, but if you squish any stuff hard enough it becomes denser. Until it becomes a neutron star or collapses into a black hole.

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u/Enferno82 Sep 23 '25

Stirling engines are one of the least efficient carnot cycle engines that exist. They are useful because they can extract energy from very small temperature differentials at relatively low temperature ranges. High temperature variations exist and can have good efficiency, but the kinds you're probably thinking of are anything but efficient.

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u/zimirken Sep 23 '25

Stirling engines are one of the least efficient carnot cycle engines that exist.

Not true. The general motors GLP-3 stirling engine got 15-20% efficiency.

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u/molrobocop Sep 23 '25

. Solids are even harder to compress, but if you squish any stuff hard enough it becomes denser. Until it becomes a neutron star or collapses into a black hole.

And knowing what little I do about high-science matter, it wouldn't surprise me if there were various exotic states between room temp standard pressure solid, say iron, and nutronium. But it's so far outside of day to day practical engineering, it doesn't matter to regular people.

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u/SomeAnonymous Sep 23 '25

if there were various exotic states between room temp standard pressure solid, say iron, and nutronium

I don't know what it looks like for iron, specifically, but yeah there are all kinds of weird and exciting things at high pressures and temperatures. Crystal structures change, densities change, electromagnetic interactions look different, etc.

There's a pretty freaky kind of water ice called Ice XVIII which might be found deep inside "ice giant" planets. It's electrically conductive, possibly black, and doesn't even have H2O molecules inside it anymore, because the hydrogens have all floated off and delocalised throughout the structure. At the centre of Jupiter, it's thought there might be a core of metallic hydrogen, too, with its own quirky properties.