Inverse design: Process dependent efficiency of compressors for use in thermodynamic cycle simulations

• A generalised method is presented for determining the internal isentropic efficiency of screw compressors and centrifugal compressors employed within an arbitrary thermodynamic process. • The method is founded on the principles of similarity theory and is employed to generate a ”process map”, comparable to an extended Cordier diagram for screw compressors and centrifugal compressors. • Applicable to both centrifugal compressors and dry-running screw compressors, the approach allows cross-technology analysis. • In addition to efficiency, key geometric parameters are identified, enabling its use for inverse machine design. A major challenge in designing and evaluating thermodynamic cycles that include compression processes lies in accurately estimating compressor efficiency. To obtain reliable efficiency assumptions, the compressors would need to be at least partially designed. To simplify compressor design for given stationary cycle parameters, this study introduces a novel inverse design method that enables direct determination of the maximum achievable compressor internal isentropic efficiency (“process maps”) and the corresponding optimal machine parameters (e.g., number of stages, rotor geometry, internal volume ratio) based on a specified set of dimensionless cycle parameters. To ensure broad applicability, both positive displacement compressors (twin-screw compressors) and centrifugal compressors are considered, and corresponding “process maps” of the best possible efficiencies are developed. For positive displacement machines, the inverse design approach becomes feasible for the first time, as traditional methods implicitly constrain the design through empirical parameters such as delivery rate. Moreover, for centrifugal compressors within the ”process maps” developed in this study, the number of stages is inherently represented – enabling a fully inverse machine design without prior stage definition. This provides a new means of determining the optimal stage configuration directly from the cycle parameters.