ABSTRACT
This chapter deals with radial flow compressors, which are the analog of centrifugal pumps. Compared with axial flow compressors, radial or centrifugal compressors have higher pressure ratios and are smaller in size. The thermodynamics of the flow are analyzed through the Mollier diagram. The concepts of degree of reaction, total to total efficiency, and impeller and diffuser efficiencies are described in the context of centrifugal compressors. Slip coefficient and its effect on the pressure rise is discussed in detail in the context of the theories of Stodola, Stanitz, and Balje. The design aspects of centrifugal compressors are described briefly. The performance characteristics are derived using dimensional analysis, and it is shown that the relevant variables are the pressure ratio, non-dimensional rotational speed, and non-dimensional mass flow rate. Just as head is plotted against flow rate for various speeds to describe pump characteristics, the pressure ratio is plotted against dimensionless mass flow rate over a range of dimensionless speeds for centrifugal compressors.
