A New Approach to Modeling Slip and Work Input for Centrifugal Compressors

Abstract

A new method of modeling slip factor and work input for centrifugal compressor impellers is presented. Rather than using geometry to predict the behavior of the flow at the impeller exit, the new method leverages governing relationships to predict the work input delivered by the impeller with dimensionless design parameters. The approach incorporates both impeller geometry and flow conditions and, therefore, is inherently able to predict the slip factor both at design and off-design conditions. Five impeller cases are used to demonstrate the efficacy of the method, four of which are well documented in the open literature. Multiple implementations of the model are introduced to enable users to customize the model to specific applications. Significant improvement in the accuracy of the prediction of slip factor and work input is obtained at both design and off-design conditions relative to Wiesner's slip model. While Wiesner's model predicts the slip factor of 52% of the data within ±0.05 absolute error, the most accurate implementation of the new model predicts 99% of the data within the same error band. The effects of external losses on the model are considered, and the new model is fairly insensitive to the effects of external losses. Finally, detailed procedures to incorporate the new model into a meanline analysis tool are provided in the appendices.

Studying the variation of the slip factor when trimming the impeller of centrifugal pumps

“…von Backström [12], [13] and [14], Harrison H. M at al. [15]. As a main reason of flow deviation in a centrifugal pump impellers it is (mainly) considered to be the socalled relative axial eddy, which leads to the decrease in the velocity u 2 c at the impeller output.…”

“…As a main reason of flow deviation in a centrifugal pump impellers it is (mainly) considered to be the socalled relative axial eddy, which leads to the decrease in the velocity u 2 c at the impeller output. The equation proposed by Stodola, used to determine the slip factor, is presented as follows [15]:…”

“…Stanitz [11], [15] proposes an equation for determining the slip factor, obtained after a theoretical study of eight centrfugal and diagonal compresor impellers, with a vane exit angle from 0 to 45 degrees. The author suggests that the slip velocity 2u c ∆ is independent of the blade angle 2b β and depends only on the step of the blades.…”

“…The author suggests that the slip velocity 2u c ∆ is independent of the blade angle 2b β and depends only on the step of the blades. The equation proposed by Stanitz, in respect to equation (3), may be presented as follows [15]:…”