Pump and Turbine Cavitation
The cavitation within pumps and turbines
Key Facts
Gyroscopic Couple: The rate of change of angular momentum () = (In the limit).- = Moment of Inertia.
- = Angular velocity
- = Angular velocity of precession.
Pump Cavitation
Apply Bernoulli's equation at the suction flange and at the water supply surface. Therefore the total head at the suction flange with the centre line as the datum is given by:The Net Positive Suction Head (NPSH) is defined as the total head at the suction flange minus the vapour pressure of water at the prevailing temperature, . It is also known as the dynamic depression head. Therefore NPSH is the net head available at the suction flange to supply the increased velocity head and the losses at entry to the impeller.
Thoma's Cavitation Factor
- When the NPSH falls to the point where Cavitation occurs then: For suction conditions to be the same for model and prototype the value of must be equal.