Cavitation of centrifugal pump

Cavitation of centrifugal pump

Centrifugal pump is widely used in petrochemical, metallurgy, water conservancy, electric power, nuclear power and other industrial fields. It carries out power transmission for liquid medium in various production devices. Its performance reliability plays a very important role in the normal operation of the device. Cavitation is an important phenomenon in the operation of centrifugal pump. It is the most common problem that affects the reliability and service life of centrifugal pump. At the same time, it is also a huge obstacle to the development of large flow and high speed. Therefore, cavitation has become an important topic in the current pump research.

Cavitation is a kind of liquid dynamic phenomenon. The basic reason of cavitation is that the local pressure drop occurs in the process of liquid flow, forming a low pressure area. According to the knowledge of physics, for a certain liquid medium, at a certain temperature corresponding to a certain saturated vapor pressure PV, when the pressure of the medium is less than PV, vaporization will occur. When the centrifugal pump is running, after the medium enters the pump suction port, the pressure is gradually reduced before the impeller does work on the medium. When the pressure is reduced to the saturated vapor pressure at the corresponding temperature, the medium will boil and vaporize, making the original flow medium appear a large number of bubbles. The bubbles contain the steam of the conveying medium and the air originally dissolved in the medium. When bubbles flow from low pressure area to high pressure area along with liquid flow, the pressure of medium rises rapidly due to the work done by the rotating impeller. When the pressure is greater than the saturated vapor pressure PV at the corresponding temperature, the bubbles will condense again into liquid phase, and a large number of holes will be formed instantly, and the surrounding liquid medium will rush to the holes at high speed and collide with each other, making the local pressure at the hole increase sharply 。 This kind of liquid hammer is a kind of impact with high strength and high frequency. Its pressure can reach hundreds of atmospheres and the frequency of water hammer is as high as 25000 times / s. The fatigue failure of the material wall is gradually produced due to the repeated load with such high frequency and high pressure.

Under some working conditions, there may be active gases (such as oxygen) dissolved in the pumping medium. With the help of the medium, a large amount of heat will be released when the gas phase condenses into the liquid phase, which will produce electrochemical corrosion on the metal, accelerate the corrosion damage speed, and cause pitting, perforation and even fracture on the metal surface. The phenomenon of liquid-phase medium vaporization, condensation and impact in the pump, resulting in corrosion and damage of metal materials, is called cavitation of centrifugal pump.


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