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A de Laval nozzle (or convergent-divergent nozzle, CD nozzle or con-di nozzle) is a tube which is pinched in the middle, with a rapid convergence and gradual divergence. It is used to accelerate a compressible fluid to supersonic speeds in the axial (thrust) direction, by converting the thermal energy of the flow into kinetic energy .
An important point to note here is that the inlet steam velocities to each stage of moving blades are essentially equal. It is because the velocity corresponds to the lowering of the pressure. Since, in a pressure compounded steam turbine, only a part of the steam is expanded in each nozzle. The steam velocity is lower than in the previous case.
The modern steam turbine was invented in 1884 by Charles Parsons, whose first model was connected to a dynamo that generated 7.5 kilowatts (10.1 hp) of electricity. [12] The invention of Parsons' steam turbine made cheap and plentiful electricity possible and revolutionized marine transport and naval warfare. [13] Parsons' design was a reaction ...
An illustration of Hero's aeolipile. An aeolipile, aeolipyle, or eolipile, from the Greek "Αἰόλου πύλη," lit. ' Aeolus gate ', also known as a Hero's (or Heron's) engine, is a simple, bladeless radial steam turbine which spins when the central water container is heated.
Frictional resistance is offered during the flow of steam through nozzles on moving and stationary blades. In most turbines, the blade wheels rotate in a space full of steam. The viscous friction at the wheel surface causes admission losses as steam passes from nozzle to wheel. The effect of partial admission creates eddies in the blade channels.
Figure shows the variation of pressure and velocity of steam through the two pressure stages of an impulse turbine. The nozzle blades in each stage receive flow in the axial direction. Some designers employ pressure stages up to the last stage. This gives a turbine of shorter length as compared to the reaction type, with a penalty on efficiency.
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The areas of both the propelling nozzle and turbine nozzle set the mass flow through the engine and the maximum pressure. While both these areas are fixed in many engines (i.e. those with a simple fixed propelling nozzle), others, most notably those with afterburning, have a variable area propelling nozzle.