Factors influencing centrifugal pump cavitation are essential considerations in the design and use of centrifugal pumps, and have been extensively studied both domestically and internationally in recent years. However, due to differing research focuses and the fact that most studies concentrate on a single parameter affecting cavitation, the research results are scattered, and some viewpoints contradict each other. This paper synthesizes a large body of domestic and international literature, comparing and analyzing the relevant research results on the influencing factors of centrifugal pump cavitation, and derives a more comprehensive understanding of the main factors affecting centrifugal pump cavitation.
Factors influencing centrifugal pump cavitation are essential considerations in the design and use of centrifugal pumps, and have been extensively studied both domestically and internationally in recent years. However, due to differing research focuses and the fact that most studies concentrate on a single parameter affecting cavitation, the research results are scattered, and some viewpoints contradict each other. This paper synthesizes a large body of domestic and international literature, comparing and analyzing the relevant research results on the influencing factors of centrifugal pump cavitation, and derives a more comprehensive understanding of the main factors affecting centrifugal pump cavitation.
1. Influence of Fluid Physical Properties
The influence of fluid physical properties on centrifugal pump cavitation mainly includes: the purity of the transported fluid, pH value and electrolyte concentration, dissolved gas content, temperature, kinematic viscosity, vaporization pressure, and thermodynamic properties.
(1) Influence of Purity (Concentration of Solid Particles): The more solid impurities in the fluid, the more cavitation nuclei will be generated, thus accelerating the occurrence and development of cavitation.
(2) Influence of pH Value and Electrolyte Concentration: The cavitation mechanism of centrifugal pumps transporting polar media (such as general water pumps) is different from that of centrifugal pumps transporting non-polar media (pumps transporting organic compounds such as benzene and alkanes). Cavitation damage in centrifugal pumps transporting polar media may include mechanical action, chemical corrosion (related to fluid pH value), and electrochemical corrosion (related to fluid electrolyte concentration); while cavitation damage in centrifugal pumps transporting non-polar media may only involve mechanical action.
(3) Influence of Gas Solubility: Foreign studies have shown that the content of dissolved gases in the fluid promotes the generation and development of cavitation nuclei. (4) Effect of Vaporization Pressure: Studies show that cavitation damage initially increases and then decreases with increasing vaporization pressure. This is because as vaporization pressure rises, the number of unstable bubble nuclei formed within the fluid also increases, leading to an increase in the number of bubble collapses, resulting in stronger shock waves and a higher cavitation rate. However, if the vaporization pressure continues to increase, causing the number of bubbles to reach a certain limit, the bubble clusters act as "layers," hindering the shock wave's propagation and weakening its intensity, thus gradually reducing the degree of cavitation damage.
(5) Effect of Temperature: Changes in fluid temperature significantly alter other physical properties affecting cavitation, such as vaporization pressure, gas solubility, and surface tension. Therefore, the mechanism by which temperature affects cavitation is complex and requires assessment based on specific circumstances.
(6) Effect of Surface Tension: When other factors remain constant, reducing fluid surface tension can decrease cavitation damage. This is because as fluid surface tension decreases, the intensity of the shock wave generated by bubble collapse weakens, reducing the cavitation rate.
(7) Influence of Liquid Viscosity: Higher fluid viscosity results in lower flow velocity, fewer bubbles reaching the high-pressure zone, and a reduced intensity of the shock wave generated by bubble collapse. Simultaneously, higher fluid viscosity also weakens the shock wave. Therefore, lower fluid viscosity leads to more severe cavitation damage.
(8) Influence of Liquid Compressibility and Density: As fluid density increases, compressibility decreases, leading to increased cavitation losses.
2. Influence of Material Properties of Flow Components
Since pump cavitation damage primarily manifests as damage to the materials of flow components, the material properties of these components will also influence centrifugal pump cavitation to some extent. Using materials with good cavitation resistance to manufacture flow components is an effective measure to reduce the impact of centrifugal pump cavitation.
(1) Material Hardness: Taking an impeller made of AISI304 as an example, cavitation causes work hardening and phase transformation-induced martensitic steel in the impeller material. This change, in turn, will prevent further cavitation. The cavitation resistance of work hardening and phase transformation-induced martensitic steel mainly depends on the hardness of the impeller material.
(2) Work Hardening and Fatigue Resistance: The higher the work hardening index of a material, the better its fatigue resistance, and consequently, the better its cavitation resistance.
(3) Influence of Crystal Structure: Under otherwise determined conditions, cavitation resistance is a function of microstructure. In cubic crystal systems, metals with body-centered cubic lattices are highly sensitive to strain rates. As the strain rate increases, rapid transgranular brittle fracture and cleavage fracture occur, leading to pitting corrosion and a higher erosion rate. For metals with close-packed hexagonal lattices, when the axial ratio is close to ideal and the cavitation environment is present, all six slip systems are activated, rapidly transforming into the stable state FCC, absorbing the work done by cavitation stress and reducing the erosion rate. For metals with face-centered cubic lattices, there are more slip systems, and under high stress, plastic flow will occur. Therefore, the incubation period is longer, and the erosion rate is lower. In summary, during cavitation, the transformation from BCC to HCP or from FCC to HCP will improve cavitation resistance. (4) Influence of Grain Size: The smaller the grain size of the metal material used in the impeller, the better its resistance to cavitation. This is because smaller grain sizes increase grain boundaries, hindering dislocation slippage and increasing resistance to crack propagation, thus prolonging the erosion life.
3. Influence of Centrifugal Pump Structural Design
