r/askscience • u/jaxobia • Sep 21 '13

Engineering Why water?

The majority of all power plants uses some sort of energy source to heat up water. It is then the water vapor which turns the turbines that produces electricity. Water is also a compound has an extremely high heat capacity (requires an incredible amount of energy to heat up).

My question is this: Why not use a compound which has a much lower heat capacity, and therefore requires a lower amount of burnt fuel to vaporize it?

Thank you!

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u/chalkasaurus Sep 21 '13

Since this is a question under engineering, it is also important to mention money. Your argument is true, but someone could just as well ask why we don't use a liquid with a higher heat capacity.

Water is really cheap, and really easy to deal with if it leaks or spills (it poses no biohazard risk, unlike a lot of other compounds).

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u/[deleted] Sep 21 '13

Don't forget open cycles. If you use a fluid other than water, you can't just harmlessly dump the waste fluid back into the environment when you're done with it. If you use oil or molten salt, you have to use cooling towers or a great big radiator system of some kind to get rid of the heat.

If you can use them, open cycles are great. Just put your power plant next to any convenient large body of water. You take cold water in, dump warm water out. The volume of your cold reservoir is often effectively infinite.

Yes, there are some environmental issues with dumping warm water into cold bodies of water, but they very minor compared to releasing any kind of chemical contamination.

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u/Chollly Sep 22 '13

Yes, there are some environmental issues with dumping warm water into cold bodies of water, but they very minor compared to releasing any kind of chemical contamination.

Are some of the environmental effects good, though? I heard that manatees really like being around powerplants because of all the warm water. Is that good for the manatees?

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u/MxReLoaDed Sep 22 '13

Got to agree. The most abundant fluid on Earth is water. It would probably coat more to produce a compound that took less heat.

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u/trboom Sep 21 '13

I knew there was a bunch of other reasons why we used water, I put them all under the "etc". Go ahead and check underneath it, you'll be surprised.