Investigation On Sediment Erosion Characteristics Of Double Suction Centrifugal Pump

Double suction centrifugal pumps are widely used in pumping stations distributed along the Yellow River. The slurry containing fine suspended sediment particles is transferred by double suction centrifugal pumps. The part abrasion of double suction centrifugal pump is a common issue, which harms the normal operation of pumps seriously. It is significant to study the sediment erosion law of double suction centrifugal pumps for improving the hydraulic performance and the operational stability.The governing equations, drag force models and sediment diffusion coefficient models are all investigated. Because the influence of turbulence is not considered in the commonly used drag force models, a modified drag force model named TE-Wen-Yu model is proposed in this study, where the inertia factor and turbulence factor are introduced. This study proves the influence of inertia term and turbulence intensity on the drag force coefficient by the inertia factor and turbulence factor. Through the experiment results and theoretical research, we propose expressions of the inertia factor and turbulence factor. Subsequently, the propose expression of drag force coefficient is determined by experimental data and the least square method, and the relation among turbulence modification function, particle Reynolds number and turbulence intensity is derived based on the inertia factor and turbulence factor expressions. The TE-Wen-Yu model is proposed by using the turbulence modified function. The calculations for sediment-laden flow in several circular tubes and an elbow pipe show that the TE-Wen-Yu model improves the accuracy of the solid-liquid two-phase flow field mainly with suspended sediment.The previous sediment diffusion coefficient models’ accuracy is not enough due to the ignoring of the particle diameters influence to the fluid turbulence intensity when they are applied for suspended sediment’s two-phase flow simulation. Thus the fluid turbulence intensity change rate function about particle diameter and solid volume concentration is derived, and an improved model of sediment diffusion coefficient is obtained in present study, which is called DC-PDPC model. The proposed function derivation is based on the semi-empirical eddy viscosity coefficient model, the particle-eddy interaction theory about the influence of the particle diameter on the fluid turbulence intensity, the equilibrium flow theory and the multivariate regression theory with experimental data. The suspended sediment’s two-phase flow simulations are conducted in some circular tubes and an elbow pipe. By comparison with the previous models, the DC-PDPC model can better reflect the influence of the particle diameter on sediment diffusion coefficient and the DC-PDPC model can be accurately applied to the suspended sediment’s solid-liquid two-phase flow with obviously improved accuracy of flow field.For the first time, both TE-Wen-Yu and DC-PDPC models are adopted to study a double suction centrifugal pump containing 25-50μm sand of 5～30kg/m3. The blade wear law is obtained, and blade erosion relation caused by sand concentration and material hardness are established. Comparing to previous models’ results, the sand concentration distribution ranges calculated by the TE-Wen-Yu and DC-PDPC models on blade pressure surface is decreased, and the solid velocity is changed. The blades are the most severe part in impeller. The blade’s erosion area increases gradually from the trailing edge to the leading edge, which mainly locates in the back of suction surface and the middle and back of the pressure surface. The blade’s pressure surface is more badly eroded rather than the suction surface. The severity erosion area is the block erosion area located in blade’s pressure surface trailing edge. Both the severity erosion area and the maximum erosion rate increase when sand concentrations increase gradually from 5kg/m3 to 30kg/m3 The increased maximum erosion rate is proportional to the increment of sand concentration. The severity erosion area is not changed by the increment of the blade’s material hardness. However, the maximum erosion rate is decreased by 50%, when Brinell Hardness of the blade increases from 300 to 600.The investigation achievements have improved the computational accuracy of the suspended load sediment solid-liquid two-phase flow field, which lay the foundation for improving abrasion resistance of double suction centrifugal pump.