Design of an Experimental ORC Expander Setup Using Natural Working Fluids
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Organic Rankine Cycles (ORC) are an efficient and cost-effective technology to generate power from waste heat. Arguably, the two most important factors affecting the performance of the Rankine cycle are the choice of working fluid and the type of expander. This potential for waste heat recovery, combined with future restrictions on some working fluids, justify the need for further research on ORC expanders using natural fluids. To the knowledge of the authors, there is no experimental data available in the open literature for flows involving natural working fluids and operating conditions representative of ORC turbines. As a result, the fluid dynamic design methodologies used for ORC turbomachinery rely on tools that have not been validated. In response to this lack of experimental data, a test rig to characterize the performance of expanders in the 25–100 kW power capacity range using natural working fluids and their mixtures will be designed and built at NTNU. This unit, officially named EXPAND, is a part of the infrastructure project HighEFF-Lab, sponsored by The Research Council of Norway. The unit was designed to operate in the gas phase to reduce the heating and cooling needs as well as the charge of working fluid. The expander architecture selected for the first experimental campaign is a variable-speed, single-stage, axial turbine operating with isobutane (R600a).