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The Power behind the Engine
If a delicate vane is held at an opening from which steam issues, the pressure of the steam will cause rotation of the vane, and if the vane is connected with a machine, work can be obtained from the steam.
When water is heated in an open vessel, the pressure of its steam is too low to be of practical value, but if on the contrary water is heated in an almost closed vessel, its steam pressure is considerable. If steam at high pressure is directed by nozzles against the blades of a wheel, rapid rotation of the wheel ensues just as it did in Figure, although in this case steam pressure replaces water pressure. After the steam has spent itself in turning the turbine, it condenses into water and makes its escape through openings in an inclosing case. In Figure the protecting case is removed, in order that the form of the turbine and the positions of the nozzles may be visible.
A single large turbine wheel may have as many as 800,000 sails or blades, and steam may pour out upon these from many nozzles.
The steam turbine is very much more efficient than its forerunner, the steam engine. The installation of turbines on ocean liners has been accompanied by great increase in speed, and by an almost corresponding decrease in the cost of maintenance.
FIG. - Steam as a source of power.
FIG. - Steam turbine with many blades and 4 nozzles.