Volute scroll, conic diffuser and sudden expansion discharge loss account for 4–6 points of efficiency decrement in a typical centrifugal compressor stage. The flow in a volute is highly comlex. It is strongly believed that understanding of the detailed flow structure in a volute will provide insights on minimizing the losses by isolating the mechanisms that contributes to entropy generation. The result will be more efficient centrifugal compressor product for customers at higher profitability levels for manufacturers. Results of an experimental and theoretical analysis of the flow inside in a single stage centrifugal compressor volute are presented. Experiments were performed at three speeds and eight mass flow rates per speed. Static pressure distributions were mapped on the vaneless diffuser and volute casings. This data gave a good understanding of the flow structure in the volute. A meanline analysis was performed using the experimental results in order to obtain the absolute velocity and flow angle leaving the impeller. The combination of the two data sets was used as boundary conditions for a theoretical analysis. Theoretical results showed the detail flow structures inside the vaneless diffuser and volute with good agreement to the experiment.

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