Effect of particle parameters on flow field and erosion wear characteristics of flow passage components in screw centrifugal pump

Abstract: Sediment erosion wears are recognized as serious engineering problems in slurry handling industries. As a kind of solid-liquid two phase flow delivery pumps, screw centrifugal pump has a wide efficiency region and non-plugging performance, however, the problem of erosion wears in it can not be overlooked. In this study, the flow field of screw centrifugal pump was simulated by using the Euler-Lagrange method when the numerical results coincide well with the experimental results. The RNG (renormalization group) k-ε turbulence model was used to solve fluid flow based on the grid-scale, and the DPM (discrete phase model) method was used to solve the information of particle motions under the particle-scale. The impact of particles to impeller and volute surfaces were calculated through the Tabakoff particle restitution coefficients formula. The grids of computational domain were generated by ANSYS ICEM (integrated computer engineering and manufacturing) software. Because of the complex structure of the screw centrifugal impeller, the tetrahedron and triangular prism hybrid grids which had strong adaptability were selected. And the grid project was thought to be suitable for computation after the grid independence test and verify. The interface between dynamic and static domain was set to frozen rotor, and also the wall free sliding function was used. The SIMPLE algorithm was used to couple the pressure and velocity of the computational domain, and the two order upwind scheme was used to discretize the N-S equation. The convergence precision as 10-4 was set when the total pressure of the pump outlet tends to be stable, and it was considered that the convergence standard was reached. We adopted the Mclaury and OKA models to predict the flow passage components erosion. By calculating and deriving the correlation factor functions contained in those two erosion models, it was found that the function of material hardness and impact angle almost had the same trend of change in two models. The hardness of material is negatively correlated with the erosion rate. With the increase of impact angle, the impact angle function of two models increased rapidly first and then tended to be stable, and reached the maximum near the 40 degree. After the overall consideration, we selected particle velocity, particle size and particle concentration as the influencing factors to analysis the erosion damage of flow passage components under different particle parameters. The results showed that the erosion of impeller was mainly concentrated at the head of pressure face, the shroud of screw part and the centrifugal part of suction face. As for volute casing, volute tongue and belly portions at the circumferential angle of 281° were found to be the most serious regions of erosion damages. Particle velocity was positively correlated with erosion, when the particle size ranged from 0.05 mm to 0.16 mm, the increase of particle size promotes erosion, and when the particle size was greater than 0.16 mm, erosion rates increased slowly. That was because the "size effect" of particles inhibited the development of erosion. The increasing of particle concentration also showed the same trend. When the particle concentration was at the range of 3% to 6%, the increasing of particle concentration would aggravate and erosion was destroyed. While from 6% to 7%, the increasing of particle concentration produced the opposite result. On this basis, the optimization direction of the hydraulic design and structural design of the solid-liquid two-phase flow pump was shown, which laid a foundation for improving the anti-wear erosion performance of two-phase flow pumps. Firstly, it decreased the blade inlet angle to reduce the impact angle between particles and the head of impeller. Secondly, it thickened the centrifugal part of suction surface properly. The third, volute inner wall thickness can be gradually increasing along the circumferential direction. Finally, as long as the whole structure permits, the volute tongue can be removable.