'A thermal power station is a power plant in which heat energy is converted to electric power. In most of the world the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator.'
Why is H2O chosen? Shouldn't a liquid with a lower boiling point be used?
Also, why can't the following setups be used? Have they all been duly considered?
1) Expanding Liquid:
In this setup, a chosen liquid is heated, expanded, and used to push pistons, without getting boiled. As a liquid is hardly compressible, shouldn't the expansion generate a tremendous pressure? Furthermore, no latent heat is involved.
2) Expanding Empty Spiked Solid in a Liquid:
In this setup, a specially crafted empty solid is heated in a liquid to give rise to a large increase in volume. The liquid then pushes a piston.
3) Strong Balanced Bimetallic Strips:
In this setup, three sets of bimetallic strips/rods are used to push a piston when cooled (and bent when heated).
4) Expansion of Ice:
In this setup, freezing H2O in cold regions, natural or artificial, expands by about 9% and is used to push pistons.
Best Answer
Expanding Liquid: the expansion per energy unit is tiny compared with the expansion at the phase transition from liquid to gas.
Expanding Solid: even worse than expanding liquid
Bimetallic strips: very little energy transfer capability and long cool-down cycle.
Ice: see "expanding solid" above.
The next best choice after conversion of (any) liquid to gas is direct gaseous expansion as is done in internal combustion engines; the latter is far less efficient.
As to the choice of water: it's easily available, relatively nontoxic , and boils at a reasonable temperature: not terribly hot, but not so low that it boils at, say, room temperatures.