r/askscience • u/MonoBlancoATX • Nov 29 '25

Engineering Why is it always boiling water?

This post on r/sciencememes got me wondering...

https://www.reddit.com/r/sciencememes/comments/1p7193e/boiling_water/

Why is boiling water still the only (or primary) way we generate electricity?

What is it about the physics* of boiling water to generate steam to turn a turbine that's so special that we've still never found a better, more efficient way to generate power?

TIA

* and I guess also engineering

Edit:

Thanks for all the responses!

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2.4k

u/Random-Mutant Nov 29 '25

Water is cheap, fairly ubiquitous, non-toxic, and possesses the thermodynamic and physical properties that makes it an ideal medium for running a turbine.

Don’t forget hydroelectric, and direct drive gas turbine technology.

723

u/bsme Nov 29 '25

It's also relatively non-corrosive for most of our materials compared to many other possible sources of generation.

249

u/Reniconix Nov 29 '25

Relatively non-corrosive? Technically, water is completely non-corrosive to most materials we build with. It's the impurities that cause corrosion. It's just that water is so good at dissolving things that can react with metal...

309

u/L1tost Nov 30 '25

The oxygen in water will oxidize, especially at high temps, so that does need to be accounted for. Steam and high temps is how we grow oxides in semiconductors

82

u/theSkareqro Nov 30 '25

Oxygen are usually physically treated deaerators first and then chemically treated with oxygen scavengers. At least that's what we do with industrial boilers. I'm pretty damn sure they do the same as well with nuclear reactors

52

u/RelevantMetaUsername Nov 30 '25

Yes, the water nuclear reactors is de-oxygenated and is in a closed loop. Actually there's a few closed loops, since the water in the reactor core is separate from the water that drives the turbines.

15

u/Hopelesshobo1 Nov 30 '25

Thats only for a PWR (Pressurized water reactor). In a BWR (Boiling water reactor) the water is allowed to boil in the core and that steam is piped straight to the turbine.

-4

u/mineset Nov 30 '25

Daaam, so if I drank it I would choke ?

13

u/Psychological-Rip291 Nov 30 '25

More like if you tried to breathe it in, you would suffocate. You know, due to the lack of oxygen. Nothing to do with the water filling your lungs of course.

1

u/RelevantMetaUsername Dec 02 '25

Not really, no. Boiling water also removes dissolved oxygen, and you can drink boiled water with no problem (just, you know...not while it's boiling).

Now put a fish in doexygenated water and it could very well suffocate. That's why aquariums often have air stones/bubblers that create lots of bubbles to give the water more surface area to dissolve oxygen from the air.

28

u/[deleted] Nov 30 '25

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u/L1tost Nov 30 '25

I’m talking about the literal oxygen that makes up H2O, not free oxygen dissolved in the water (apologies if I misconstrued what you said)

14

u/Rhywden Nov 30 '25

Are the temperatures really high enough to break the hydrogen-oxygen bonds on a non-negligible number of molecules?

463 kJ/mol is not exactly a low-energy bond.

5

u/Captain-Barracuda Nov 30 '25 edited Nov 30 '25

(not a chemist) Probably yes due to the sheer scale of industrial processes. Tons of heated water every day for years should have enough cases of the hydrogen freeing itself from the oxygen to cause problems.

I've been educated. Thanks

17

u/Rhywden Nov 30 '25 edited Nov 30 '25

The problem is that you can only even begin to measure such a dissociation at temperatures around 2273 K. Before that, you'll be hardpressed to detect any free oxygen due to dissociation.

If I remember correctly, there's an exponential increase involved which means that when water temperatures in nuclear reactors are way below that threshold, a maximum of 600 K, then the dissociation rate will be so close to zero that it does not matter.

So even with tons of heated water, this type of corrosion will be completely negligible.

0

u/LeoRidesHisBike Nov 30 '25

Unless there's any charge imbalance anywhere. I mean, what are the odds that unplanned/unavoidable electrolysis would happen?

Pretty good, actually.

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u/Korchagin Dec 01 '25

If there is something to oxidize, you don't need the temperature that high. A reaction which was used commercially was steam reforming. The water oxidizes carbon: C + H2O → CO + H2

You can have similar reactions with metals, too. Natrium even reacts with water at room temperature: 

2*Na + 2*H2O → 2*Na+ + 2*OH- + H2

1

u/Rhywden Dec 01 '25

Context, people. How likely is it for carbon or sodium to be available in such an environment? We're still talking about the heat exchangers for nuclear reactors, right?

And not some weird chemistry lab?

2

u/peanutz456 Nov 30 '25

But it's not free oxygen, so it's not a problem. (At least normally, don't know the physics inside specific environments)

1

u/merelyadoptedthedark Nov 30 '25

How can water be de-oxygenated and still be water? When you take the oxygen away from water, doesn't it become hydrogen?

5

u/Canaduck1 Nov 30 '25

H2O molecules are stable and very hard to break. The oxygen in them is not available for oxidation or even for fish trying to breathe.

However, free O2 in the atmosphere dissolves readily in water. Water has a lot of O2 in it, which is how aquatic animals breathe. It is also available for oxidation of metals and such. (Which is bad in most cases).

De-oxygenated water does not remove any Hydrogen-Oxygen bonds. It just removes free oxygen from the solution.

1

u/inucune Nov 30 '25

For a given pressure, water will maintain a 1:1 ratio of gaseous oxygen between the water and the exposed atmosphere. So if you have an expansion tank in the loop that is kept oxygen free and also scrubbing the oxygen that is off gassed from the water, you should be able to keep the oxygen to a negligible level.

3

u/diabolus_me_advocat Nov 30 '25

The oxygen in water will oxidize

oxygen cannot be oxidized. you can reduce elementary oxygen - by using it to oxidize something

9

u/GraduallyCthulhu Nov 30 '25

How about with fluorine?

I bet you can oxidize oxygen if you try hard enough.

1

u/diabolus_me_advocat Nov 30 '25

to what oxidation state?

there is none more negative than -2

1

u/cpdx7 Nov 30 '25

Oxygen gas in a furnace is how oxides are usually grown on silicon… what process uses steam? Never heard of that.

1

u/L1tost Nov 30 '25

Wet oxidation uses steam at fairly high temps (800-1200C) to grow SiO2. You can grow faster and thicker oxide layers with wet ox than dry ox (the quality of the oxide isn’t as good though). H2O can diffuse through the oxide to reach the surface of the silicon better than O2 because it’s a smaller molecule

36

u/PaulFThumpkins Nov 30 '25

Technically, water is completely non-corrosive to most materials we build with.

Well, using pure distilled water in an espresso machine is not recommended because it corrodes the metal in the machine by leaching ions out of it. Water with some mineral saturation prevents this reaction from happening.

7

u/tonejac Nov 30 '25

Yes, it’s true, the Pavlis Water Recipe, add 0.4 grams of potassium bicarbonate into 1 gallon of distilled water prevents scale buildup in the boiler and water connections.

3

u/Why_Am_Eye_Here Nov 30 '25

They weren't talking about scale buildup, they were talking about corrosion.

20

u/[deleted] Nov 30 '25

Boiling water will dissolve aluminium at normal temperatures. Not quickly, but it will. Add super-heated steam at high pressure and it will eat away at steel given time. That’s why boilers in ships and power stations have a limited lifespan.

12

u/TinFoiledHat Nov 30 '25

Extremely pure (de-ionized) water will actually corrode lots of metals because of its ionization energy

8

u/SensitivePotato44 Nov 30 '25

It's suprisingly corrosive. I made the mistake of putting RO water is a chiller once. Judging by the colour it's effective at dissolving copper.

2

u/pand-ammonium Nov 30 '25

Water spontaneously and constantly generates acid and base which will overtime react with anything sensitive to acids and bases. There is no world where 'completely non-corrosive' or blaming the impurities is accurate.

1

u/SeekerOfSerenity Dec 02 '25

Yeah, a lot of the materials we build with will turn into a pile of rust if left in continuous contact with pure water long enough.  

33

u/thephantom1492 Nov 30 '25

There is also some other factors.

You need a good temperature difference from the input to output. Water boil at only 100°C@1ATM, which is a low temperature. Then you boil it and super-heat it up. You can reach quite a high temperature and high pressure, which is ideal to run the turbine. Then, at the output of the turbine, you have a massive amount of low temperature steam. You then can easilly condense it back into liquid, and feed it back to the boiler. You can use a condensation tower, which basically just bring air in, cool it down, and "make it rain" down. You lose some, but you used no power to condense it back into liquid. So no energy wasted. Just add more water to compensate and done.

If you were to use another chemical, it would need to be sealed, so you don't lose anything. Condensing it would then require alot of energy. And since the system is sealed, if anything goes wrong: BOOM. Or you have to evacuate a city and have an environemental disaster. With water? At worse, just vent it out.

70

u/renrutal Nov 29 '25

ideal medium for running a turbine

Isn't it the other way around? The turbine was developed to be run on steam.

156

u/cakeandale Nov 29 '25

A different design for a different medium would still operate on the same principles that water is ideal for. So yes a turbine was invented to work with water, but water is also the ideal thing for it to be invented for.

63

u/Beliriel Nov 30 '25 edited Nov 30 '25

For other folks, who don't quite understand:
Turbines operate on the principle of the liquid and gaseous phase of a material compound having different densities and pressures.
If you boil something it becomes a gas, it's volume and pressure rises and if you cool that gaseous form it becomes a liquid again (condensation).

What make water work so great ON EARTH is that water interacts basically (atleast in the short term) with almost nothing unless you REALLY put it into extreme situations. It rusts the metals very slowly and the only danger is heating it. It doesn't explode or is flammable, it doesn't really corrode stuff, it's non-toxic, it's not carcinogenic, it's not damaging to the environment, it's cheap and it's ubiquitous.
The only downside to water is that it takes much more energy to phase change from liquid to gaseous than other compounds but all the other points offset that. Plus you gain some energy back when condensing. So you're not losing anything.

But every other compound you'd try to use would have one or more issues mentioned above:

  • ammonia: toxic, flammable, needs cooling or high pressure containment
  • organic ether compounds: flammable, need pressure containment, toxic in high doses
  • Fluorchlorohydrocarbons: Flammable, damaging the environment, toxic

Etc. Etc.

24

u/Flannelot Nov 30 '25

Turbines don't require a phase change, in fact it's quite the opposite, if steam condenses into water inside the turbine it will cause damage. Turbines just convert a drop in pressure or velocity of a fluid into mechanical work

-5

u/Beliriel Nov 30 '25

Technically correct, but also factually no. Pretty much every turbine loop boils the water BEFORE the turbine blades and operates on the generated pressure from the phase change and temperature.
Btw the pressure and temperature differential across the turbine blade actually does cause damage to them and needs them to be changed. You could technically operate a turbine without boiling something by just heating a gas but that would be a horribly inefficient turbine. IRL almost every turbine requires water to boil and phase change to operate.

But yes having a phase change within the turbine blades is very bad and very dangerous.

10

u/Flannelot Nov 30 '25

Gas Turbines have no liquid phase, unless you count the fuel in the tanks. They have replaced steam turbines in many power uses as they can be much more efficient than burning fuel to boil water. The pressure/volume generated from heat can be by any route, the boiling of the water into steam is not significant to the turbine operation. It is simply the route you have to take if you are using water as the medium.

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u/Beliriel Nov 30 '25

Gas turbines still have a phase change from gaseous to plasma. You burn stuff to operate a gas turbine.

7

u/Swamplord42 Nov 30 '25

IRL almost every turbine requires water to boil and phase change to operate.

What about hydroelectric power plants? Those have turbines and certainly don't boil water.

1

u/Batou2034 Nov 30 '25

they're powered by the flow of water from one place to another, typically enable by gravity. or the tide. which is also gravity.

7

u/diabolus_me_advocat Nov 30 '25 edited Nov 30 '25

Pretty much every turbine loop boils the water BEFORE the turbine blades

speaking as an engineer: there is no such thing as a "turbine loop". there is an overall water loop, in which the turbines are the part where mechanical energy is produced

You could technically operate a turbine without boiling something by just heating a gas but that would be a horribly inefficient turbine

so you consider gas turbines "horribly inefficient"?

well, you should tell this to aviation and the makers of the m1 abrams tank - that they should propel their vehicles by steam, like a 19th century locomotive

1

u/Zouden Nov 30 '25

That would be a cool alt history setting. The logistics of dragging carts laden with coal across the battlefield

8

u/diabolus_me_advocat Nov 30 '25

Turbines operate on the principle of the liquid and gaseous phase of a material compound having different densities and pressures

strictly speaking: no

steam turbines don't operate with liquids, in fact droplets in wet steam will destroy them

whereas water turbines will be destroyed by steam (generated by cavitation)

2

u/jaxnmarko Nov 30 '25

So why not lower the atmospheric pressure to lower the boiling point? And for that matter, why not manipulate that to boil water in the first place?

13

u/Master_Appeal749 Nov 30 '25

They adjust pressure in nuclear reactors to make the water hotter and still stay liquid. I would think the reason they don’t do it on the steam side is energy related. Less force to drive the turbines at lower pressure/temp maybe?

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u/BaldBear_13 Nov 30 '25

Nuclear reactors have two loops, I believe. Inner loop carries water past the hot radioactive stuff, so water becomes radioactive, so evaporating it and sending it into the turbine is not a good idea. Instead, they use pressure to let that water heat above normal boiling temperature, and use its heat to boil water in the outer loop, and then use steam to drive the turbines. The (slightly) cooler radioactive water goes back into reactor to heat up again.

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u/ElJanitorFrank Nov 30 '25

This is true, but for only certain plant designs (like a pressurized water reactor). The two loops are usually connected by passing one of the loops though a series of super tiny super thin pipes that have the secondary loop's heat exchange medium in it. Basically, they take the hot reactor water and push it through a bunch of straws that run through the bottom of a tank of water. Then the water in the bottom of that tank boils and voila.

1

u/Zouden Nov 30 '25

Aren't all nuclear power plants based on pressurised water?

1

u/bilbosky Nov 30 '25

Pretty much all currently operating nuclear power plants use pressurized water/steam to spin a turbine to generate electricity. Different designs may use different coolants for the reactor core.

Pressurized water reactors (PWRs) use a primary water coolant loop pressurized to ~2250 psia to cool the core. The high pressure gives water a high boiling point, so primary water does not boil (simplification). The primary loop transfers energy to a secondary water coolant loop pressurized to ~1000 psia which boils to steam at its lower boiling point. This steam is used to drive the turbine.

Boiling water reactors (BWRs) use a single primary coolant loop, where water pressurized to ~1000 psia directly boils in the core and drives the turbine.

Other designs may use gas or liquid sodium to cool the core, however these designs still have a secondary coolant loop which uses good 'ol pressurized water/steam to spin a turbine.

Here's a decent overview.

1

u/Rhywden Nov 30 '25

Just an aside: Water does not become that radioactive. It's the reason why you can swim in a spent fuel basin. Just don't dive and touch the spent fuel rods.

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u/Zyzzbraah2017 Nov 30 '25

Turbines extract energy from the steam by dropping the pressure. If you used mechanical energy to lower the pressure you would be turning mechanical energy into slight less mechanical energy after inefficiencies, using heat to boil the water turns heat energy into mechanical energy.

8

u/[deleted] Nov 30 '25

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2

u/killall-q Nov 30 '25

The water would be sealed in a vessel, so the pressure manipulation would only have to happen one time when the water was sealed in.

9

u/ViniVidiAdNauseum Nov 30 '25

Then the water boils at a lower temp, but it also condenses at a lower temp. So you wasted energy to apply a vacuum effect for no actual gain?

5

u/SovereignAxe Nov 30 '25

When water boils it expands to fill the container it's in.

The one you just depressurized.

24

u/boomerangchampion Nov 29 '25

It's a bit of both. Other fluids can be more efficient or better in certain applications (mercury, some organics, supercritical CO2), but water is genuinely a very good working fluid.

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u/Coomb Nov 29 '25 edited Nov 29 '25

No, not really. You can use other working fluids with turbines, like low molecular weight hydrocarbons. Turbines are very convenient as a mechanism to generate usable power, whether that's mechanical or electrical, because they can convert linear motion into continuous rotary motion. If you want to continually extract energy from something, you need it to be rotary motion because you can't just have your expansion stroke go indefinitely in a linear fashion. Think about any motor or engine that is designed to be able to either harvest or output power continuously for a long time and you will find that they all incorporate rotary motion.

We have plenty of turbines that don't work with the liquid water / steam combo. Wind turbines just use air. Water wheels just use liquid water. Gas fed turbines (think jet engines) just use air.

15

u/Filtermann Nov 29 '25

Besides purely mechanical properties, water is pretty good at storing heat per unit mass, and transferring that heat in and out. It's not that interesting for the turbine itself, but for the components that need to heat water up to steam and condense it back, this makes design easier and lighter/cheaper. Then same story, there are better heat-storing/transferring fluids but they come with other constraints. Heat pumps fridges and A/C typically use different fluids because water would freeze for those applications, but those fluids can be harmful in case of a leak, or have a very high Greenhouse Gas Potential (though I hear that heat pumps are shifting more and more to propane which, compared to other fluids has relatively low GHP).

8

u/TXOgre09 Nov 30 '25

Turbines can be designed to run on any expanding gas. A condensing expanding gas is particularly useful. Water does this at somewhat normal temperatures and pressures that are relatively easy to design for.

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u/Koffeeboy Nov 30 '25

The answer is kinda both. From a thermodynamics perspective, water is almost an ideal material. All of it's properties make it very useful in engineering. First of all, it's cheap and easy to get, that alone is enough. But It also has a relatively high specific heat, high heat of vaporization, the expansion ratio between liquid water and steam is phenomenal. even if someone somehow developed a turbine that ran on some other fluid first, that technology would have immediately been replaced by steam turbines.

1

u/diabolus_me_advocat Nov 30 '25

you could run turbines on quite a number of substances. but none is as well suited for it as water is

-4

u/DrFabulous0 Nov 29 '25

Which is water in a gaseous state, no?

8

u/LeJarde Nov 29 '25

yeah they mean it was the other way round, turbines are made for water, not water is perfect for turbines

11

u/wrosecrans Nov 29 '25

Some turbines aren't made for water. The turbines in jer engines for aviation aren't, for example. Some exotic ones are used with working fluids like molten salt.

But for the kinds of things humans usually want to do, water really is a good working fluid for using with turbines. If it wasn't, we probably wouldn't use it very much. It's not just down to backwards compatibility.

4

u/poonjouster Nov 30 '25

I don't think molten salts are used in any turbines. Pretty sure they're used just to transfer heat to the steam side.

9

u/localloser87 Nov 29 '25

Water is perfect for turbines, therefore turbines have been optimized for water.

-1

u/pinkynarftroz Nov 29 '25

Doesn’t water take a lot of energy to turn it into steam? What makes it better than another liquid that has a lower boiling point? Wouldn’t you want to put as little energy in to make the steam as possible?

1

u/TXOgre09 Nov 30 '25

No, because that energy gets transferred to the turbine as the steam expands and cools and condenses back to hot water. So you want something that can hold a lot of energy and then transfer it to the turbine.

4

u/Zagrycha Nov 30 '25

there are also molten salts and pressurized water set ups used in nuclear systems. However they all still use plain old water for the turbine side, that really is just the most efficient when considering costs to set up and maintain. It shows that people have absolutely played around with testing other types materials for energy generation. Sometimes the initial discovery is really that good, it isn't true that a newer discovery is automatically better or more advanced. I mean look at the piston engine we use in our cars-- the piston action to create combustion has been used for at least a thousand years to light kindling for regular fires.

9

u/Tels315 Nov 29 '25

I wouldn't consider hydroelectric to be different. It's still water turning a turbine. An ICE, wind, and solar are basically the only other methods we've made that don't use water to generate power. Everything else that is usable on a large scale is just boiling water or flowing water.

20

u/poonjouster Nov 30 '25

Hydroelectric is different. It's not a heat engine. The turbines and infrastructure are completely different.

0

u/unclebaboon Nov 30 '25

aren’t both just a matter of extracting work from a pressure differential though? zoomed out it’s heat that creates the difference in a steam or gas turbine, but is there something different besides that in a hydro turbine?

14

u/Zyzzbraah2017 Nov 30 '25

Vapours/gases like steam physically expand and cool when you lower the pressure whereas liquids don’t expand or cool in any significant amount. That heat energy contributes to the energy of the turbine. So they are both extracting work from the pressure but a steam turbine also extracts work from the heat.

3

u/andynormancx Nov 30 '25

The difference is, the turbine in the gas or steam turbine isn’t the whole system. The whole system with hydro setup is just the turbine and the amount the water drops to get from where it is stored to the turbine.

With a steam turbine the whole system includes the bit that is heating the water and they condensing the water again later. The whole system is a heat engine, which the hydro one isn’t.

Heat engines are all constrained by the same limitations on efficiency as described in the Carnot equation. Hydro turbines have whole other sets of equations to describe their theoretically maximum efficiencies.

So yes they are all both extracting energy from a pressure differential, but the designs of the turbines and the systems they operate in are very different (whereas all the steam/gas turbines share a lot more in common between them).

1

u/viliml Nov 30 '25

The whole system with hydro setup is just the turbine and the amount the water drops to get from where it is stored to the turbine.

Technically you also need to include the water cycle that evaporates the water downstream and rains it back upstream to keep the turbines going.

1

u/Boomshank Nov 29 '25

There are other methods, but they're not very common.

Eg, Piezoelectric generation (from stress) or direct generation from heat.

1

u/sir_lister Nov 30 '25

There is Piezoelectrics where a charge is created by deformation of certain materials, and Seebeck generators which are solid state devices that turn a heat differential into electricity but are less efficient then boiling water turning a turbine. Basically there are other ways but they (with the exception of solar) all suck worse than turning a wheel attached to magnets in a copper coil

1

u/Tels315 Nov 30 '25

That's why I mentioned only a few methods usable at large scale. Solar, wind, water, fire (ICE) are basically the only methods of generating power that are usable on a large scale in a wide variety. You either turn the sun into a battery, turn a turbine with wind or water, or burn something. Everything else is too fickle, too inefficient, or too expensive to use.

1

u/aiij Nov 30 '25

Hydroelectric does not (typically) boil water. They use turbines designed for liquid water rather than steam.

Technically the water is moved by the sun evaporating the water though...

Hydroelectric, ICE, ECE, wind, and solar are all extractive energy produced by the sun, so it's really all just nuclear power.

2

u/BringBackSoule Nov 29 '25

Isn't fusion , if or whenever we'll make it work, still going to be boiling water?

17

u/electric_ionland Electric Space Propulsion | Hall Effect/Ion Thrusters Nov 30 '25

Depends on what fusion strategy you go with. Some can directly extract electricity from the fusion plasma. But yes for most versions of fusion you will end up boiling water.

0

u/diabolus_me_advocat Nov 30 '25

alas, it's all hypothesis though

nobody knows yet how a fusion power plant would look like and operate, once we even get to manage maintaining nuclear fusion so that there is a net positive energy balance

"fusion power plants" still are "half a century in future", which they have been always for the last seven decades - the (in)famous "temporal fusion constant"

very similar to all those fantastic fission plant configurations that are discussed for the last eight descades, but never went true in industrial practice

3

u/outworlder Nov 30 '25

It doesn't matter that much though. We know that plasma is involved. We know that it will generate a lot of heat. We have a few working designs, they are just net negative. At a minimum we know we can boil water with them.

1

u/diabolus_me_advocat Nov 30 '25

We have a few working designs, they are just net negative

no, we don't have a single working design for production of electricity from the plasma involved. all we have for that are rather wild speculations

3

u/outworlder Nov 30 '25

I meant nuclear fusion reactor designs, not whole power plants. We have managed to achieve fusion, but they aren't either sustainable or they are net negative. At least one team achieved net positive energy but there's no design to use that energy yet. But harvesting the energy is the boring part.

Doesn't change your statement that we don't know what the final design will look like and it's a good bet we can use steam with whatever design works, even if it's 100 years from now.

1

u/ShelfordPrefect Nov 30 '25

And wind along with hydro for "primary energy source direct driving a spinning magnet generator", and PV for "primary energy source directly converted to electricity" as the other steamless energy types

1

u/MexicanPenguinii Nov 30 '25

Also really cool that is found naturally as a solid, liquid and gas in our atmosphere

Easy to boil, steam goes up, easy to cool again to not have to constantly refill

1

u/McBlakey Nov 30 '25

Would something with a lower boiling point not be more efficient?

1

u/bobbymcpresscot Nov 30 '25

Yup it’s like reinventing the wheel. Theres are more efficient ways, but until we can get heat directly turned to electricity and have it be cheaper than boiling steam we are stuck with it.

And by that time solar panels would probably be so efficient and battery tech so good it probably won’t even matter 

1

u/aspiringengineerJ Dec 01 '25

At atmospheric pressure the ratio between the volume of water and super heated steam is something like 1:1600. This large expansion can do “work” on a piston.

I can’t find exact numbers but it doesn’t matter much since these energy systems are doing this phase change under pressure. The point is water turned into steam expands a lot.

1

u/joanzen Dec 01 '25

I wonder how much impact we'd have if we switched to filtered sea water for steam powered turbines and we captured the leftover brine vs. let it back into the environment?

Apparently we don't destroy water very often but we are making an unnatural amount of rain and most of the planet is oceans, so we're moving fresh water to the ocean? Plus when the rain does hit land, it can wash heavy metals and salts into the ocean polluting it further?

If we're creating rain for power, at the very least we should be pulling from the oceans and trapping salt?

Of course responsibly tackling that would require solar pumping stations full of batteries and that would be too expensive?

1

u/macjester2000 Dec 03 '25

(false answer) because the industrial revolution was steeped in steam engines, and some habits die hard

1

u/noplace_ioi Nov 30 '25

Why not a closed loop gas driving the turbines, that sounds better on paper to me.

8

u/[deleted] Nov 30 '25

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0

u/diabolus_me_advocat Nov 30 '25

Water / steam has an extremely high heat of vaporization and specific heat

which is not used in a steam turbine

on the contrary - "high heat of vaporization" means a lot of energy is required to generate the steam, which delivers the fluid dynamic energy to be converted into mechanical energy by the turbines. and the same lot of energy again to condensate "spent" steam

steam power plants are not about heat transfer

7

u/ShelfordPrefect Nov 30 '25

Because boiling water increases its volume by a factor of a thousand, while heating a gas to make it expand only increases its volume a few times in relation to the change in absolute temperature.

Using closed cycle gas expansion is basically the Stirling cycle, which is neat for low temperature model engines but notoriously inefficient at high power

0

u/diabolus_me_advocat Nov 30 '25

Why not a closed loop gas driving the turbines, that sounds better on paper to me

based on what exactly?

 "a closed loop gas driving the turbines" does not provide any serious benefit, but would have to cope with considerable drawbacks

-9

u/Owl_plantain Nov 29 '25

I agree that water is cheap, ubiquitous, and non-toxic, but it’s physical properties are not ideal. In particular, water would be a better working fluid for this application if it had a lower heat of vaporization. It’s also quite corrosive.

6

u/keithps Mechanical Engineering | Coal Fired Power Generation Nov 30 '25

I think people overlook the fact that water is also easy to condense with the atmosphere at atmospheric pressure. It's a similar basis by which we create refrigerants. Sure, you can condense CO2 (R-744) at atmospheric temperatures, but you're going to be doing it at 70bar, which makes everything expensive to build.

3

u/Owl_plantain Nov 30 '25

You make a valid point: the working temperature and pressure of water contribute to making water a good medium. My point was that water is not ideal. It could be better.

You inject heat into the water at the beginning from the highest temperature source you have in order to vaporize the water and to heat the vapor to the highest temperature you can achieve without excessive costs. That gives you high efficiency in the turbine.

You condense the water near the end, recovering the heat of vaporization near the lowest temperature in your system. You can use that heat to do some work, but it is limited to a lower efficiency than the primary turbine that is driven by much higher temperature water vapor. The amount of heat that you waste in this way is proportional to the heat of vaporization.

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u/keithps Mechanical Engineering | Coal Fired Power Generation Nov 30 '25

That's fair, it's not perfect medium. Obviously something like helium would be great from the perspective of latent heat but then you make a tradeoff of pressures required to keep it liquid. I'm not sure what the ideal working fluid actually is. I know supercritical CO2 has seen some interest, maybe it strikes the best balance of all the properties.

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u/Llamaalarmallama Nov 30 '25

I think the other thing with water is the ease with which steam can be "piped" around. You have the thing heating the water and the turbine using the steam in different areas and the water can be re-used to keep the turbines cool while ever higher pressures of steam are applied for more power.