Centrifugal pump delivery head and flow rate drop effectively during the pumping of viscous fluids. Several methods and correlations have been developed to predict reduction rate in centrifugal pump performance when handling viscous fluids, but their results are not in very good agreement with each other. In this study, a common industrial low specific speed pump, which is extensively used in different applications, is studied. The entire pump, including impeller, volute, pipes, front and rear sidewall gaps, and balance holes, is simulated in Computational Fluid Dynamics and 3D full Navier Stokes equations are solved. CFD results are compared with experimental data such as pump performance curves, static pressure in casing, and disk friction loss. Dimensionless angular velocity and leakage rate are investigated in sidewall gap and efficiency variation due to viscosity is studied. The results demonstrate that the behavior of the fluid in sidewall gap is strictly sensitive to viscosity. Increasing viscosity improves the volumetric efficiency by reducing internal leakage through wear rings and balance holes, causing, however, a significant fall in the disk and overall efficiency. Results lead to some recommendations for designing centrifugal pumps which may be used in transferring viscous fluids.

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In this paper, the flow in the impeller sidewall gap of a low specific speed centrifugal pump is analyzed to study the effect of wear ring clearance and the resultant through-flow on flow field in this cavity and investigate the overall efficiency of the pump. Centrifugal pumps are commonly subject to a reduction in the flow rate and volumetric efficiency due to abrasive liquids or working conditions, since the wear rings are progressively worn, the internal leakage flow is increased. In the new operating point, the overall efficiency of the pump cannot be predicted simply by using the pump characteristic curves. The flow field is simulated with the use of computational fluid dynamics and the three-dimensional full Navier–Stokes equations are solved using CFX software. In order to verify the numerical simulations, static pressure field in volute casing and pump performance curves are compared with the experimental measurements. The results show that, for the pump with minimum wear ring clearance, the disk friction efficiency is the strongest factor that impairs the overall efficiency. Therefore, when the ring clearance is enlarged more than three times, although volumetric efficiency decreases effectively but the reduction in overall efficiency is remarkably smaller due to improvement in the disk friction losses.

The objective of this paper is to develop the shape of an existing volute so that the radial forces in off-design condition become minimum. For this purpose 3-D inverse design method based on the 3-D viscous flow calculations was applied to re-design the geometry of the volute of a low specific speed pump. Various aspects of the geometry change independently to achieve the best one which produces less radial force in off design conditions. Measurements included time-averaged values of velocity and static pressure at a large number of locations in the volute.