Lecture 1
Chapter Five
Turbines

Turbines
• Steam turbine is used to generate the mechanical power to drive the
generator in steam power plant
• In early stages, utilizing the steam power was done by reciprocating
engines
• The impulse principle: Change of momentum equals the impulse
force

Impulse Force calculation
Flat Plate

Impulse Force calculation (2)
Flat Plate

Impulse Force and power (1)
Flat Plate
• Power can be found as:
• Note that the power equals zero if VB = 0, or Vs = VB
• Efficiency: by dividing the power by initial power of jet
• By differentiating the power with respect to VB and equating the
result to zero:

Impulse Force and power (2)
Flat Plate
• W
Which means that the maximum power equals to one half the power
of jet

Impulse Force and power (1)
Cylindrical Plate

Impulse Force and power (2)
Cylindrical Plate
Now, instead of flat plate, consider a cylindrical blade that allows the
jet to reverse direction (180 degrees), relative velocity at inlet (Vs – VB),
Absolute velocity at exit (VB - (Vs – VB)) = 2VB – Vs. Then, Impulse Force is
change in momentum:
And Power equals to:

Impulse Force and power (3)
Cylindrical Plate

Impulse Force and power (4)
Cylindrical Plate