Effects of scaling on the energy efficiency of oil pumps

Abstract

Multistage centrifugal oil pumps have been used in oil production for about a century. The design of their stages has not changed for a long time, only the geometric dimensions vary, which still makes it possible to improve the performance characteristics of pumps. One of the widely used methods of changing the geometric dimensions of the stages is the scaling of stages to other dimensions. Pressure and flow characteristics of scaled stages are recalculated by similarity criteria and practically coincide with the results of bench tests. The efficiency of stages scaled from larger to smaller dimensions is always lower than that of the original stages. The purpose of this work was to establish the reasons for this phenomenon. The influence of such factors as the flow channel roughness, leakage and disk friction was evaluated. It is shown that roughness and leakage are the determining factors. The similarity method showed that as a result of scaling the effect of roughness can be reduced and even compensated by increasing the shaft speed, which was confirmed by calculations and bench tests.