Naked Science Forum

Non Life Sciences => Technology => Topic started by: brainzlol on 06/01/2013 11:37:04

Title: Ice expansion to drive motor?
Post by: brainzlol on 06/01/2013 11:37:04

When water turns to ice it expands by approx 9%.
This expansion does exert a very large force...don't know how much?
Can an engine be made to use this force?
The motor needs to amplify the small/slow "travel", at the expense of the large force.
I know we have to spend energy to cool the water, (but we then dump the ice, not reheat it)

Any ideas please?
Thanks
brainzlol (on twitter)

Title: Re: Ice expansion to drive motor?
Post by: CliffordK on 10/01/2013 04:56:14

Potentially it is possible.  However, it would be a very slow engine, and if it used linkages to amplify the motion, there would be significant power lost in the linkages.  Ice is also a relatively good insulator, so it isn't always easy to freeze a large chunk of ice.

One would need to have easy access to a cold environment, as well as liquid water.  Arctic sea ice in the winter might be one possibility where one has cold weather above the ice, and lots of water below it, although then one would be dealing with salt water.

I suppose one could also use well water in winter conditions. 

I think the pressure could be calculated by looking at the expanded phase diagram of water. (http://ergodic.ugr.es/termo/lecciones/water1.html)  I believe all types of ice other than type 1 ice have a lower density of water.'

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fergodic.ugr.es%2Ftermo%2Flecciones%2Fphase.gif&hash=094b2860f8a7903d409d484c01e4f2cb)

So, the liquid, 1h, III triple point is about 207.5 MPa, or about 30,000 PSI at -22°C, so that would be the maximum pressure one could get from the formation of ice.

Also keep in mind the specific heat of fusion of water (at 0°C, and 1 ATM) is about 80 cals/gram, or the amount of energy required to be removed to freeze 1 gram of water is about equivalent to dropping (or raising) the temperature by 80°C.  However, the specific heat of vaporization is about 540 cals/gram.

Anyway, your engine likely could be built with slow cycling, but it would likely have a large size to power ratio, and may only be applicable to very few cold winter environments.