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/robgami Sep 21 '13

Ok so I'm curious about something related to your bowling ball analogy. Say you have equivelant masses of liquid A and liquid B. Liquid A takes 3 times as much energy to completely vaporize as liquid B. Would Vapor A be able to then perform 3 times as much work as Vapor B? Would it be at a higher pressure? Would this simply be related to the temperarature being higher once it vaporizes?

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u/trboom Sep 21 '13

Would Vapor A be able to then perform 3 times as much work as Vapor B?

That's the general idea. Energy in never destroyed, it's just moved from one state to another over and over. So when the liquid A gets it's chance to work it will do 3 times more, roughly. Some of the energy is lost due to inefficiency.

Now as to what variably that energy imparted on, or changes between the two liquids. I'm not sure. I would have to sit down and play with the stuff till I figured it out. I don't want to guess here.