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Saturday, 13 December 2014

Losses in Steam Turbines

Losses in Steam Turbines Points : Losses in Steam Turbines The steam turbine work create device operation at fairly high speed has number of losses happening in it. These losses as put jointly result into extensive loss of energy. Thus, as selecting a turbine due consideration should be compensated to the losses in turbine. A few of the losses occur in turbine stages as some are outside to stage. These losses are explain ahead. 1. Disc Friction Loss This is a type of loss of energy evident when any entity says disc is turning in air or other medium. The disc would cut atmosphere and inform motion to close air. There shall constantly exist relation motion among solid wall of object and air or immediate fluid. Due to this relation movement surrounding medium constantly exerts a resistance to motion of moving point. This might result in loss of energy due to friction which can be felt through increase in enthalpy of nearby fluid. In case of steam turbines also rotor is entirely surrounded through the steam which offers resistance to rotor motion. The loss of energy of rotor can go into steam enveloping it. 2. Losses at Inlet and Exit Loss on inlet of steam turbine occurs at variable valves at access At these valves which can be stop valve or governor valves the throttling loss commonly occurs causing lowering of toward the inside steam pressure. At exit of steam turbine steam turn out to be wet and fluid now is combination of water droplet and steam. Due to moisture of steam at way out end water particle being heavier reason loss of kinetic energy. This water element, if in extreme quantity might also endanger the turbine blade. The kinetic energy of fluid at exit of steam turbine is a whole loss and in theory fluid leaving turbine should have the lowly possible energy in it. This loss of energy can be of order of 10 – 13 per cent. 3. Losses in Moving Blades In steam turbine point steam is made-up to glide easily over moving blades after exit nozzles or set blades. In definite turbine stage through flow of steam over moving blade, there can be number of factors cause loss of energy as given below:

(i) Blade friction might incur frictional loss which is taken into explanation with blade friction factor.
(ii) Boundary layer separation can occur due to sharp deflection of fluid in blade passage. Deflection results in centrifugal force which causes solidity by concave surface with the rarefaction near convex surface of blade, so resulting in division of boundary layer.
(iii) Loss of power can be due to turbulence at exit of preceding row of nozzles due to limited thickness of nozzle way out edge. There is mixing of steam jet exit nozzles and ingoing moving blade.
(iv) Loss of energy is too there due to break of flows which occur ahead the impingement of steam ahead the leading edging of moving blade. This is too term as impingement loss. These losses are fewer if flow is laminar as evaluate to turbulent flow.
(v) Loss of energy too occurs through passage of steam as of one stage to other explicitly rows. This loss is also term as carry over loss. This carry over loss is minimum if spacing among successive rows is kept small.
4. Losses in Nozzles Steam turbine nozzle is planned for isentropic increase so as to effect in enlarges in velocity as of inlet to exit. Almost in a nozzle steam exit nozzle can not have velocity equal to planned velocity value. This difference in working state of nozzle can occur as of non-isentropic expansion. The cause for non-isentropic expansion can be friction losses among the steam and nozzle wall, viscous friction resistance to flow in steam particle, boundary layer creation and division, heat loss through flow and so on. 5. Losses in Bearings Turbine bearings are important parts to hold high speed revolving of shaft. Usually, a loss to tune of 1% of turbine output occurs in bearings. Although this loss depends upon oil viscosity, bearing weight, speed of shaft, bearing surface area and film thickness and so on. 6. Windage Loss Windage loss happens as rotor blades come in contact by near fixed fluid (steam). In case of part admission turbines that are usually impulse turbines there is churn of steam in expanse having no active steam in steam turbine. As moving rotor blades come in contact by inactive steam then there is move of energy as of blade to steam. This loss of energy as of rotor to fluid is term as ‘windage loss’. 7. Losses Due to Radiations Radiation losses too happen in steam turbines, while they are extremely small compare to other losses and can be neglect. In case of steam turbines the high temperature steam is partial to small part of case so losses are small. But radiation losses are fairly important in gas turbines. In order to stop radiation losses the pipings, turbine casing etc. carrying hot fluid must be well insulate. 8. Loss Due to Leakage Steam leakage can happen across the turbine shaft and among stages. Leak of steam can result in accessibility of less work as of stage as steam is not entirely utilized for produce work. Leak occurs through flow as of one stage to other or as of one row to other during the clearance gap among diaphragm and shaft. Leak too occurs across the blade tip. Leak transversely diaphragm occurs in equally impulse turbine and reaction turbine stages. Leak across tip is not major in case of impulse turbine as pressure dissimilarity is extremely small. Tip leakage is major in reaction turbine stages.

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