Experimentally validated pre-design maps and performance estimation methods for small-scale turbopumps for organic rankine cycles

The organic Rankine cycle (ORC) system is considered a promising technology to exploit thermodynamic potential of waste heat. Small-scale ORC applications, including both vehicular applications and stationary power plants, would greatly benefit from more compact and efficient pumps, improving performance and reducing installation and operational costs. This paper provides updated pre-design diagrams and reduced-order models that incorporate the effects of tip clearance and splitter blades in small-scale high-speed turbopumps for ORC applications. A parameterized design tool has been developed to enable the rapid generation of numerous turbopump geometries. The design tool creates a dataset of numerous turbopumps with different geometrical parameters. The turbopumps are investigated with CFD analysis, and the accomplished results are analyzed to characterize the influence of tip clearance and splitter blades on the performance (slip factor and head rise) of small-scale ORC turbopumps. The numerical results are employed to infer dimensionless maps (specific speed-specific diameter) and reduced-order models, which enable the capturing of the influence of down-scaling in the early design process of such machines. In the next step, two turbopumps are designed using the new design tool and then tested experimentally to validate the numerical model. The good agreement between experimental performance characteristics and developed models validates the computational results and reduced-order models. Following the experimental validation, the performance of an ORC system designed for waste heat recovery from truck engines is estimated using the performance characteristics of the experimental turbopumps instead of a commercial multi-stage centrifugal pump. The designed small-scale turbopumps are one order of magnitude more compact compared to commercial systems. Further, the comparison suggests that the designed turbopumps improve the targeted ORC thermal efficiency by 0.51% and reduce the ratio of the turbine power consumed by the pump by 42% and 67%.