Reasons For Cavitation Of Centrifugal Low-temperature Pump

Dec 08, 2024

If the centrifugal low-temperature pump generates noise and vibration during operation, accompanied by a decrease in flow rate, head, and efficiency, and sometimes even cannot work, and during maintenance, it is often found that there are pitting or honeycomb like damages near the blade inlet edge. In severe cases, the entire blade may have this phenomenon, and even the blade may be penetrated, which is caused by cavitation damage.

The reason for cavitation in centrifugal low-temperature pumps is that the pump works on the liquid through the rotating impeller, increasing the energy of the liquid. During the interaction process, the velocity and pressure of the liquid change. Usually, the inlet of the impeller of a centrifugal low-temperature pump is the place with the lowest pressure. If the pressure in this area is equal to or lower than the vaporization pressure of the liquid at that temperature, a large amount of steam and gas dissolved in the liquid will escape from the liquid, forming many small bubbles mixed with steam and gas. When these small bubbles flow with the liquid to the high-pressure zone, a pressure difference is generated due to the vaporization pressure inside the bubbles, which is greater than the vaporization pressure around the bubbles. Under this pressure difference, the bubbles are compressed and burst, and then re condense. During the condensation process, liquid particles accelerate from all sides towards the center of the bubble. At the moment of condensation, the particles collide with each other, generating high local pressure. If these bubbles burst and condense near the metal surface, the liquid particles will continuously hit the metal surface like countless small bullets. Under continuous impacts with high pressure and frequency, the metal surface gradually deteriorates due to fatigue, which is commonly referred to as erosion. There are also some active gases (such as oxygen) mixed in the generated bubbles, which chemically corrode the metal with the heat released during the condensation of the bubbles. The combined effect of chemical corrosion and mechanical erosion accelerates the rate of metal damage, which is known as cavitation damage.

When the centrifugal low-temperature pump begins to experience cavitation, the cavitation area is small and has no significant impact on the normal operation of the pump. There is also no obvious reflection on the pump performance curve. But when cavitation develops to a certain extent, a large number of bubbles are generated, which affects the normal flow of liquid and even causes interruption of liquid flow, resulting in vibration and noise; At the same time, the flow rate, head, and efficiency of the pump have significantly decreased, which is also evident on the pump performance curve. When severe, the pump cannot work.
In order to avoid cavitation as much as possible, during the process design, the liquid should have a certain degree of supercooling before entering the pump, and the pump body should be installed at a lower position to provide a certain static pressure head at the liquid inlet. In addition, it is important to pay attention to cold insulation and minimize cold losses as much as possible.