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Comparison of Scroll, Screw, Roots, Piston Expander, and Tesla Turbine for Small-Scale Organic Rankine Cycle

This study compares the performance of different expanders in a small-scale organic Rankine cycle, including scroll, screw, roots, piston, and Tesla turbine. The experimental setup and a semi-empirical model were used to analyze the advantages and operating maps of each expander. The results show that the scroll expander has the highest isentropic efficiency, while the Tesla turbine is the most volumetrically efficient. The study also discusses perspectives and economic aspects of these technologies.

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Comparison of Scroll, Screw, Roots, Piston Expander, and Tesla Turbine for Small-Scale Organic Rankine Cycle

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  1. Comparison of a scroll, a screw, a roots, a piston expander and a Tesla turbine for small-scale organic Rankine cycle Parraleldisk, viscouseffects O. Dumonta, L. Tallurib, D. Fiaschib, G. Manfridab and V. Lemorta aThermodynamics Laboratory, University of Liège (Belgium) bDepartment of Industrial Engineering,  Università degli Studi di Firenze (Italy)

  2. Table of contents

  3. IntroductionState of the art • Stronginfluence of expanderon ORC performance • (Almost) no experimentalcomparison of expander in litterature • No single technologyidentified as optimal (cost, efficiency, compactness, working conditions..) • 3 main technologies : Scroll, Screw, Piston (+roots+tesla)

  4. Experimental setupHydraulic scheme • Test-rig : 3 kWeORC (SUN2POWER) • Fluid : R245fa and ~5% oil (but not for piston) • Scroll: AC/DC convertor + variable resistor • Piston : Asynchronousgeneratorwithfour quadrants variable-frequency drive • Screw : Air-cooled Eddy-currentbrake • Roots: modifiedenginesupercharger • Tesla : Prototype from Firenze university

  5. Table of contents

  6. Important note • Important note • Perfectly objective comparison between different types of expanders not possible : • Different level of maturity for expanders • Not an expander sized for the test-rig (mass flow, pressure and temperature affect the performance of the expanders (not necessarily in the same way for each one). • Sizing fluids for those expanders are not the one used in this ORC (R245fa). • Nominal working conditions in terms of pressure and temperature are different for each technology (higher pressure and temperature for the piston for example). • BUT: • No such a comparison in litterature • Same test-rigand fluid • Modelscalibrated to predict optimal performance

  7. Semi empirical modelAdvantages • Semi-empirical model • Low CPU time + robust + extrapolation + generalformalism • Supply DP, mechanicallosses, leakage, under(over)-expansion, heattransfers • Calibration of 7 parametersbased on experimentation • Performance extrapolation with speed optimisation • Tesla deterministic model • 2D code for the viscous flow solution, considering real compressible fluid properties

  8. Table of contents

  9. ModelAssumptions • Larger range of pressure ratio explored • Largerefficiency for the screw and scroll • Rather constant efficiency for the piston and Tesla

  10. ModelOperating maps Optimal performance of a machine for a given condensation and supplytemperaturetemperature !!!All axis are positive!!! Extreme conditions Flexibility Lowtemperature Efficiency

  11. Table of contents

  12. Conclusion Screwexpander minimum power ~10 kW  wrong! Scroll expander are the best because of higherisentropicefficiency  wrong! Piston expander not interestingbecause of lowefficiency  wrong! Not a single volumetricexpanderisthe optimal solution! Tesla optimal for low volume ratio • Perspectives • Maturity of technology • Other technologies: Vane, Wankel, … • Economic aspects

  13. Conclusion - Tesla  The mostvolumetric of the turbines

  14. Important note • Important note • Perfectly objective comparison between different types of expander not possible : • Different level of maturity for expanders • Not an expander sized for the test-rig (mass flow, pressure and temperature affect the performance of the expanders (not necessarily in the same way for each one). • Sizing fluids for those expanders are not the one used in this ORC (R245fa). • Nominal working conditions in terms of pressure and temperature are different for each technology (higher pressure and temperature for the piston for example).

  15. Thankyou! olivier.dumont@ulg.ac.be Open source papers http://orbi.ulg.ac.be 15

  16. Semi-empirical modelsExtrapolation • Optimal conditions not reached on the test-rig model to extrapolate • Oh = 5 K (Tamb=25°C) • RPM optimised • RpadjustedwithPexp,ex 10 bar 30 bars

  17. Experimental resultsIsentropic efficiency • Same trend for eachtechnology • Low pressure ratio  over-expansion losses • High pressure ratio  under-expansion, mechanicallosses and pressure drops • Higher scroll efficiency • Lowefficienciesbecause of test-rig limitations (pressure drops, mass flow rate…)

  18. Semi-empirical modelOperating maps Optimal performance of a machine for a given condensation and evaporationtemperature !!!All axis are positive!!! Extreme conditions Flexibility Efficiency

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