Steam turbines are used to generate mechanical power from steam to drive generators in steam power plants. Early steam power was generated using reciprocating engines. Turbines use the impulse principle where the change in momentum equals the impulse force. For flat plates, the maximum power occurs when the velocity of the blade is half the initial jet velocity. For cylindrical plates, the jet reverses direction by 180 degrees, resulting in an exit velocity of 2VB - Vs. The impulse force is the change in momentum and power can be calculated from the impulse force and velocity.
2. 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
5. 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:
6. Impulse Force and power (2)
Flat Plate
• W
Which means that the maximum power equals to one half the power
of jet
8. 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:
