Olshtynskyi P. Taking Account of Flow Pattern Features in Diffusers to Improve the Engineering Performance Standard of a Centrifugal Pump

This dissertation presents an effective method of reducing the specific metal content of a multistage centrifugal pump, in maintaining at the same time its performance, by designing its stages having the minimum outer diameter-to-entry diameter ratio, which is achieved due to the application of a built-in diffuser featuring a discontinuous transfer zone. The subject matter of the paper is mainly an investigation of the flow pattern in the diffuser elements and of the effect of the geometric features forming an transfer zone upon the flow pattern in the transfer zone and in the return flow passages as well as upon the hydraulic losses. The study of the effect of the geometric features that form an transfer zone upon the flow pattern has allowed to refine the mathematical model of flow within the transfer zone, thus making possible, by-turn, to evaluate the flow angle at the inlet of the return flow passages. By using the results of physical and virtual experiments, the minimum outer diameter- to-entry diameter ratio and specific speed have been connected by a relationship, at which a reduction in the stage efficiency is not yet observed. Procedural guidelines for designing diffusers with a discontinuous transfer zone have been worked out. Hydraulic passages of the pump stage comprising a diffuser with the outer diameter-to- entry diameter ratio = 1.39 have been developed. The application of this stage in the multistage centrifugal pump has enabled to improve its engineering performance standard as a result of reducing its specific metal content, with the efficiency maintained at the same level as an analogous pump has.