Available NPSH in turbine (Net Positive Suction Head)
In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation:
1. The Available NPSH (NPSHA): a measure of how close the fluid at a given point is to boiling, and so to cavitation.
2. The Required NPSH (NPSHR): the head value at a specific point (e.g. the inlet of a pump) required to keep the fluid from cavitating.
NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation.
The calculation of NPSH in a reaction turbine is is based on the fact that the cavitation will first occur at the outlet of the impeller, at the entrance of the draft tube.
|NPSH||Available NPSH in a turbine (m)|
|p0||Total pressure at the lower free surface (m-1*kg*s-2)|
|ρ||Density of the fluid (kg/m3)|
|pv||Pressure of vapor (m-1*kg*s-2)|
|ze||Elevation of the tube entrance (m)|
|z0||Elevation of the lower free surface (m)|
|hf||Turbines minor losses (m)|