Exploring the Limits of Heat Engines with Ice Expansion

[shanepitts]

Noting that ice expands by about 9%, why isn't it possible ot build a heat engine from this natural process?

 

[russ_watters]

It would be possible, but I'm not sure what the benefit would be. It could generate a huge force, but with very slow motion.

 

[shanepitts]

It would be possible, but I'm not sure what the benefit would be. It could generate a huge force, but with very slow motion.

Are there any contemporary ice engines in use?

 

[.Scott]

You could. The freeze-thaw cycle makes it for a slow engine. It is possible to use this method for quarrying granite - drill holes, fill with water, let it freeze and thaw, repeat with more water. And, of course, that process occurs naturally in the process of destroying roads and bridges.

 

[russ_watters]

Are there any contemporary ice engines in use?

Not that I know of.

 

[Mark44]

You could. The freeze-thaw cycle makes it for a slow engine. It is possible to use this method for quarrying granite - drill holes, fill with water, let it freeze and thaw, repeat with more water. And, of course, that process occurs naturally in the process of destroying roads and bridges.

This process occurs naturally in breaking up exposed rock surfaces, causing what is called "exfoliation."

 

[phinds]

Are there any contemporary ice engines in use?

If it were economically useful there probably would be so the fact that there aren't any suggests that it's not and that would be why.

Think about it. In order to produce any meaningful amount of electricity you would have to let nature freeze a huge amount of water and doing so would take many days, possibly weeks. Then you would have to wait another year for it to happen again. What would be the use of such a generator?

 

[CWatters]

It would be possible to make a heat engine that used the expansion of ice but it's generally harder to cool something than it is to heat something. You need to do work to remove energy from water to make it freeze.

 

[sophiecentaur]

Isn't there something to do with Thermodynamic Efficiency that would make a poor heat engine which just relied on change of state?
I seem to remember that efficiency involves the temperatures of the hot source (T_h ) and the cold source (T_c)
η= 1 - T_c/T_h
iirc and that would lead suggest low efficiency unless it could be arranged that the two temperatures could be kept well apart. In the case of a steam engine, where change of state is also involved, the temperature difference can be usefully high but ice, being a solid, would hard to pump around in the same way. Perhaps the ice / water could be held as an emulsion in some oil?
Such an engine would need to operated in a polar region (say Antarctica), where you would get the cooling for free - but in a massive cooling matrix.

 

[russ_watters]

Heat engines can't just rely on change of state, they need a pressure change otherwise the working fluid doesn't even move. For this, you'd have a huge pressure increase associated with the small temperature change and flow rate.

For normal heat engines, a large temperature difference means higher efficiency, but I'm not sure if that applies here, since the cycle is kind of upside down. But heat transfer is easier with larger delta-t's, which severely limits the power of such a device. Want to heat water faster? Just add more 1500F fire. Want to freeze it faster? Sorry, no -1000F heat sink available.