Steam turbine

A steam turbine extracts the energy of dry pressurized superheated steam as mechanical movement. Energy is force acting over distance. In a Parsons-Westinghouse steam turbine nozzles apply supersonic steam to a curved blade. The blade whips the steam back in the opposite direciton, simultaneously allowing the steam to expand a bit. A stationary blade then redirects the steam at the next blade. The process repeats until the steam is completely expanded. The moving blades are mounted radially on the rotor. The stationary blades are mounted to the case of the turbine.

Steam turbines of this type have some weak spots. First, some steam leaks through the annulus where the of the shaft penetrates the casing. Usually this is limited by some sort of rotating labyrinth, but it can be a problem, especially on the high-pressure end of the turbine. Also, most steam turbines are very particular about what they expect in their feed. Water droplets can quickly damage a steam turbine if the turbine blades have not been designed to withstand the presence of water droplets.

The turbine described above was invented by Charles A. Parsons, and improved by George Westinghouse.

A number of other types of turbines have been developed that work effectively with steam:

The De Laval turbine accelerated the steam to full speed before running it against a turbine blade. This was good, because the turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam. It is also, however, less efficient.