Comparative Analysis of Radial and Tangential Diffuser Centrifugal Pumps, at Varying Specific Speeds

In this study, three centrifugal pumps, with specific speeds -dimensionless parameters used to assess pump performance -of 19, 27 and 42, were numerically investigated to evaluate the influence of diffuser type on radial-flow pump performance.For each specific speed, the radial and tangential diffuser configurations were paired with identical impeller geometry, ensuring a one-to-one comparison at the same head (20 m) and rotational speed (2800 rpm).The specific speeds correspond to flow rates of 250, 500, and 1200 L/min, respectively.The results show that low specific speeds exhibit greater unsteadiness, with head fluctuations decreasing from approximately 4 m at nq : 19 to approximately 0.5 m at nq : 42.At low specific speeds, the radial diffuser generates a higher head due to reduced flow separation; however, as specific speed increases, the tangential diffuser produces a higher head, consistent with its ability to accommodate stronger tangential momentum.Although the radial diffuser displays slightly larger instantaneous head fluctuations at nq : 27 and 42, it experiences lower hydrodynamic force levels than the tangential diffuser at the same operating conditions.This distinction highlights that head fluctuation and surface-integrated force response are governed by different mechanisms.The systematic comparison across three specific speeds provides new insight into diffuser selection, demonstrating that appropriate diffuser geometry enhances hydraulic efficiency, suppresses unsteady flow structures, and reduces loading on volute surfaces.These findings provide practical guidance for the design of diffusers in centrifugal pumps.