Abstract

The realization of commercial mini organic Rankine cycle (ORC) power systems (tens of kW of power output) is currently pursued by means of various research and development activities. The application driving most of the efforts is the waste heat recovery from long-haul truck engines. Obtaining an efficient mini radial inflow turbine, arguably the most suitable type of expander for this application, is particularly challenging, given the small mass flow rate, and the occurrence of nonideal compressible fluid dynamic effects in the stator. Available design methods are currently based on guidelines and loss models developed mainly for turbochargers. The preliminary geometry is subsequently adapted by means of computational fluid-dynamic calculations with codes that are not validated in case of nonideal compressible flows of organic fluids. An experimental 10 kW mini-ORC radial inflow turbine will be realized and tested in the Propulsion and Power Laboratory of the Delft University of Technology, with the aim of providing measurement datasets for the validation of computational fluid dynamics (CFD) tools and the calibration of empirical loss models. The fluid dynamic design and characterization of this machine is reported here. Notably, the turbine is designed using a meanline model in which fluid-dynamic losses are estimated using semi-empirical correlations for conventional radial turbines. The resulting impeller geometry is then optimized using steady-state three-dimensional computational fluid dynamic models and surrogate-based optimization. Finally, a loss breakdown is performed and the results are compared against those obtained by three-dimensional unsteady fluid-dynamic calculations. The outcomes of the study indicate that the optimal layout of mini-ORC turbines significantly differs from that of radial-inflow turbines (RIT) utilized in more traditional applications, confirming the need for experimental campaigns to support the conception of new design practices.

Highlights

  • The development of low-capacity high-temperature organic Rankine cycle (ORC) power systems is increasingly pursued, because the creation of large markets for distributed renewable energy conversion and mobile/stationary heat recovery is deemed possible [1]

  • The results of the computational fluid dynamics (CFD) simulation are compared to the results provided by the meanline model, in which the number of blades is assumed equal to the optimal value found through CFD optimization

  • Targeted CFD simulations were used to investigate if this observation applies to ORC radial inflow rotors characterized by large volumetric flow ratios

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Summary

Design Method and Performance

The realization of commercial mini organic Rankine cycle (ORC) power systems (tens of kW of power output) is currently pursued by means of various research and development activities. Obtaining an efficient mini radial inflow turbine, arguably the most suitable type of expander for this application, is challenging, given the small mass flow rate, and the occurrence of nonideal compressible fluid dynamic effects in the stator. The preliminary geometry is subsequently adapted by means of computational fluid-dynamic calculations with codes that are not validated in case of nonideal compressible flows of organic fluids. An experimental 10 kW miniORC radial inflow turbine will be realized and tested in the Propulsion and Power Laboratory of the Delft University of Technology, with the aim of providing measurement datasets for the validation of computational fluid dynamics (CFD) tools and the calibration of empirical loss models. The outcomes of the study indicate that the optimal layout of mini-ORC turbines significantly differs from that of radial-inflow turbines (RIT) utilized in more traditional applications, confirming the need for experimental campaigns to support the conception of new design practices.

Introduction
Radial-Inflow Turbine Layout
Averaging procedure
Loss Breakdown
Assessment of Stator–Rotor Interaction Effects
Assessment of Part-Load Performance
Assessment of the Optimal Solidity of the Impeller
Findings
Conclusions
Full Text
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