Steam Turbine

A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. 

Steam turbines utilize the principle of allowing pressurized steam to expand in controlled stages. Each turbine can be composed of a number of impulse and reaction turbines, each of which allows the steam to expand and turn the blades, or buckets, within the device. Most steam turbines employ both of these variations in concern, with the impulse turbines operating under high pressure, and low pressure being utilized for the reaction turbines. The difference between the two is that the impulse turbine uses a nozzle to introduce high velocity steam into the rotors, while the rotors in reaction turbines are themselves a type of nozzle.

The arrangement of impulse and reaction turbines within a steam turbine can effectively make the system very efficient. By making use of both high and low pressure, and having the steam do work at each stage of its expansion, the process may remain highly isentropic. This simply means that the entropy that goes into the system is similar to that which comes out. The other benefit of the design is that the spinning of the turbines creates rotary motion, which can be ideal for both power generation and turning paddles or other drive mechanisms on ships.

The modern steam turbine was invented in 1884 by Sir Charles Parsons, whose first model was connected to a dynamo that generated 7.5 kW or 10 hp of electricity. 

 

parson's turbine

A number of other variations of turbines have been developed that work effectively with steam. The de Laval turbine invented by Gustaf de Laval accelerated the steam to full speed before running it against a turbine blade. De Laval's impulse turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam, but is considerably less efficient.

 

de laval turbine