How is the required net positive suction head for a centrifugal pump generated?

This post was last edited by 3983596_FPPZ on 2019-2-26 08:22. The energy of a liquid consists of pressure energy and kinetic energy; pressure energy is the static pressure, while kinetic energy is related to velocity. These two forms of energy can be converted into each other under different conditions, but their total amount remains constant, which is the principle of conservation of energy. When liquid enters the inlet of the impeller, due to the horizontal flow, the impeller has not yet done any work, so the total energy of the liquid at that point remains almost unchanged. However, the flow velocity increases as a result of the suction effect exerted by the liquid at the impeller’s outlet (with a small portion of this increase being due to the slight work done by the rotating blades). As a result, part of the pressure energy of the liquid is converted into kinetic energy, leading to a decrease in pressure. But as long as the reduced pressure remains higher than the vaporization pressure of the liquid, cavitation does not occur. In summary, the required net positive suction head (NPSHR) of a pump is an energy representation method, where NPSHR equals the value of pressure reduction at the impeller inlet due to increased flow velocity (energy). The better a pump’s resistance to cavitation, the lower its pressure drop and its NPSHR. To ensure that the liquid does not vaporize even after this pressure drop at the impeller inlet, it is necessary that the energy at the pump inlet (the net positive suction head available) be such that NPSHA is greater than or equal to NPSHR plus the vaporization pressure energy plus 0.5. On page 59 of the Modern Pump Design Manual, it is stated that NPSHR represents the pressure drop at the pump inlet (this is the definition of NPSHR), and it serves to prevent cavitation in the pump. It is required that the liquid at the pump inlet possess an energy imparted per unit weight, equal to or greater than the head corresponding to its vaporization pressure (this statement is not a definition, but rather a further explanation of it)

The Bernoulli equation specifies the difference between the net positive suction head available in a system and the required net positive suction head; this difference is generally 0.5 m, while for special fluids it is 1 m

This post was last edited by foam_ZPTK on 2019-3-4 15:10; calculations were performed using Bernoulli’s equation