Cavitation pumps and propellers

Mecaflux functions,saturation vapor pressure,exemples ,screen shots

the phenomenon of cavitation on pumps or propellers, explanation:

It is possible to evaporate a liquid, without varying the temperature, lowering the ambient pressure below the saturation vapor pressure .

When the liquid is sucked into a pipe,its pressure decrease. if this pressure is lower than its saturation vapor pressure, the liquid begins to boil . This phenomenon is called cavitation.When one wants to draw water column around 10 meters, the water vaporizes and releases the gas that fills the vacuum, thus it is impossible to pump more than 8-10 meters by suction. We must therefore place the pump in the bottom of the well ... These pressure drops below the saturation vapor pressure can be very localized on the top surface of Profiles submerged or narrowed areas of pumping device. Bernoulli tells us that the acceleration of the fluid generates a pressure drop ..... These decreases internal pressure pumps are described by the NPSH pump.

The cavitation is a formation of vapor bubbles due to pressure drop.

In forming, the bubbles increase the fluid's volume in the low pressure area. Increasing pressure generate condensation of bubble wich violently imploding. The shocks created by the bursting of bubbles destroy the walls of the organs in contact with the fluid. The cavitation causes wears of pumps.

Cavitation must be avoided, and the design of a thruster this must be verified. Much information on the cavitation characteristics of propellers is obtained from model tests. They are made in cavitation tunnels where the ambient pressure can be reduced in order to cause such cavitation under conditions of controlled observation.

Another phenomenon is taken into account in hydrodynamics or pumping : ventilation