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Impulse Turbine

D-laval is a steam turbine which consists of Nozzle and one row of moving blades .the high

 pressure steam from boiler is completely expanded in the nozzle because of this there is enthalpy

drop and increase K.E of nozzle .high velocity jet when impinges moving blades rows give the

axial thrust & tangential thrust and K.E is converted to Mechanical energy.the velocity of steam

with which it leaves the nozzle is very high.otational speed of steam is very high

!pproximately "#$### to %#$### pm

 The steam supplied

to a single- wheel

impulse turbine

expands

completely in the

nozzles and leaves

with absolutevelocity C1 at an

angle a1, and by

subtracting the blade

velocity vector U,

the relative velocity

vector at entry to the rotor V1 can be determined. The relative velocity V1 maes an

angle o! b1 with respect to U. The increase in value o! a1 decreases the value o! the

use!ul component, C1 cos a1 and increases the value o! the axial or "ow component

Ca sin a1. The two points o! particular interest are the inlet and exit o! the blades.

these velocities are V1 and V#, respectively

Velocity Diagram of Impulse Turbine:

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f the blade is symmetrical then '()'* and neglecting the friction effects of blades on the steam

+  ,()+  ,*.

n the actual case the relative velocity is reduced by friction and expressed by a blade velocity

co-efficient .

Formulas:

1.

Workdone by

steam

 

wt =U (cw1+cw2)  

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2.   Relative velocity at blade inlet   

 Applying the cosine rule¿ the ∆ ABC   

v 1=√ b c2+√ c d

2

 3. Relative velocity at rotor outlet is:

 

v 2= Kv1  

4. Velocity of !irl at inlet

 

". Velocity of !irl at outlet

 

#. $%ial component at inlet

 

&. $%ial component at outlet

 

'. $%ial forces on bla(es

 

). Tangential forces on bla(es

 

*+. ,or (one on bla(es

 **. la(e spee(

*2. Inlet angle of la(es

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*3. /utlet angle of bla(e.

 sin β2=ca2/v 2

 

14. Efciency o blading

 

$aximum e%ciency o! blades & cos2❑⍶

*". 0oer (evelope(

 

*#. 1pecific steam consumption3600

(cὼ1+cὼ 2)U 

1'.(peed )atio⍴=U  /c1

1*.$ass +lowm=

 AV V   = AV  / x V s

m=  ∗1000

(cὼ1+cὼ2)∗U 

*). umber of bla(es:

numbero! blades= "d +15

#.

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