The reason of low temperature centrifugal pump cavitation: pump through the rotation of the impeller on the liquid work, so that the liquid energy increases. In the interaction process, the velocity and pressure of the liquid changes. In general, the inlet of the impeller of the centrifugal pump is the place where the pressure is lowest. If the pressure is equal to or lower than at the temperature of liquid vaporization pressure, there will be steam and dissolved in the liquid gas from the liquid in a large number of escape, lots of steam and gas mixture, the small bubble formation. These small bubbles with the liquid flow to the high pressure zone, due to the vapor pressure inside the bubble, and around the bubble greater than vaporization pressure, pressure difference is generated. Under the pressure difference, the bubble burst and re condensed. In the condensation process, the liquid particles from all around to the bubble center to accelerate movement, in the condensation of the moment, the particles collide with each other, resulting in a high local pressure. These bubbles, if they break down near the metal surface, are condensed, and the liquid mass is like a myriad of small bullets, hitting on the surface of the metal. Under high pressure and high frequency, the surface of the metal is gradually destroyed by fatigue, which is often referred to as erosion. In the bubble generated by the inclusion of a number of active gases (such as oxygen, etc.), with the heat released by the bubble condensation, the metal from the chemical corrosion. Chemical corrosion and mechanical erosion of the common role, it is more accelerated the speed of metal damage, this phenomenon is the phenomenon of cavitation damage.
At the beginning of the centrifugal pump cavitation, the cavitation area is small, the normal work of the pump has no obvious effect, and there is no obvious reflection of the pump performance curve. But when the cavitation development to a certain extent, resulting in a large number of bubbles, the normal flow of the liquid, and even cause fluid flow interruption, vibration and noise; pump flow, head and efficiency is obviously decreased at the same time, on the pump performance curve also showed obvious. Serious when the pump can not work. In order to avoid cavitation phenomenon, in the process of design, should make the liquid in the pump before the degree of cooling, at the same time the pump should be installed in the lower position, so that the liquid inlet has a certain static pressure head. In addition to pay attention to the cold, as far as possible to reduce the loss of cold.
