Steam Turbines


A steam turbine is rotary machine which is designed to convert the energy of high pressure and high temperature steam into mechanical power.The operation of steam turbine wholly depends upon the dyanamic action of the steam.

Introduction to steam turbines

. A steam turbine is rotary machine which is designed to convert the energy of high pressure and high temperature steam into mechanical power.The operation of steam turbine wholly depends upon the dyanamic action of the steam.


.In this process the steam is first expanded in a set of nozzels or passages upto exit pressure where in the pressure energy of the steam is converted into kinetic energy.You can imagine nozzel as of fire fihting people hold in there hand to spray water.


.The nozles are fix to the casing.If the resultant high velocity steam is passed over the curved vanes or blades,the steam changes its direction and it would leave in the direction 180 degree .


.Due to this pressure the change in momentum and it will exert a resultant force on the blades.If thes blades are attached to a disc on a rotor or shaft which is free to rotate, the resultant force would cause the rotor to rotate.Thus the motive power is developed.The principal of operation of steam turbine is its forcing effect.


.A pair of ring of nozzles fixed to the casing and a ring of moving blades fixed to the turbine rotor is CALLED A STAGE OR A TURBINE PAIR.Both the blades moving and fixed are so designed that the steam jet shall not strike the blades but it should glide over in the direction of blade surfaces.

Types of steam turbines
Two types are there:

(A) IMPULSE TURBINE:

.These turbines use the principal of impulse in which the kinetic energy of steam obtained after passing over a ring of fixed nozzles is used to exert a force on a ring of moving blades.
.The pressure of the steam while passing over the moving blades remain constant and its kinectic is converted to mechanical energy.The examples of impulse turbines are De-Laval,Curtis and Rateau etc.

(B)REACTION TURBINES

.In case of areaction turbines, there is a continous pressure drop of steam while passing over the rings of fixed and moving blades.Accodingly,the moving blades passages are suitably designed for steam to expand,therefore these blades also act as nozzles.


.The reactve force along that due to change in momentum of the steam provides the motive force for the turbine to develop power.It folows that these turbines are basically the impulse-reaction turbine but in practice these are called reaction turbines.Examples of such a turbine is PARSON'S reaction turbine.


.Mostly the steam turbines are axial flow type in which the steam flows over the blades in direction parallel to the axis of turbine rotor.


.The only important radial flow turbine is LUNGSTROM reaction turbine in which the steam enters at the blade tip nearest to the axis of the wheel and flows towarsd the circumference.

I think I am able to give brief review of steam turbines.If you think some think more should be added ,please let me know.


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