Effects of Impeller Design and Surface Roughness on the Performance of Centrifugal Pumps

Abstract

Conventional methods of designing centrifugal pump impellers are based on the ideal velocity triangles and the Euler head equation. Empirical modifications derived from the performance of previous successful designs are used to correct for departures from these ideals, and design procedure becomes a matter of extrapolating from past experience. More fundamental studies of the flow conditions inside a centrifugal pump have been made, but these have generally required simplifications of the impeller geometry or other expedients in order to render the problem amenable to analysis. In consequence, the results have found only limited application for the complex pumps and real fluids met in practice. In the paper the author attempts to reconcile these different approaches by presenting data on the effects of the various impeller design elements on the performance of a 2-in. double-entry pump. The decisive parameters determining the performance of the impeller are shown to be the number of blades and their outlet angle. The inlet angle and the blade profile are of relatively minor importance. Roughness of the impeller surfaces, both internally and on the outside of the shrouds, decreases the pump's efficiency but increases its output. Analysis of the test results with artificially roughened impellers demonstrates that current conceptions of disc friction and the energy balance sheet for a pump are untenable.