Organic Rankine Cycle (ORC) power systems are receiving increased recognition for the conversion of thermal energy when the source potential and/or its temperature are comparatively low. Mini-ORC units in the power output range of 3–50 kWe are actively studied for applications involving heat recovery from automotive engines and the exploitation of solar energy. Efficient expanders are the enabling components of such systems, and all the related developments are at the early research stage. Notably, no experimental gasdynamic data are available in the open literature concerning the fluids and flow conditions of interest for mini-ORC expanders. Therefore, all the performance estimation and the fluid dynamic design methodologies adopted in the field rely on non-validated tools. In order to bridge this gap, a new experimental facility capable of continuous operation is being designed and built at Delft University of Technology, the Netherlands. The Organic Rankine Cycle Hybrid Integrated Device (ORCHID) is a research facility resembling a state-of-the-art high-temperature ORC system. It is flexible enough to treat different working fluids and operating conditions with the added benefit of two interchangeable Test Sections (TS’s). The first TS is a supersonic nozzle with optical access whose purpose is to perform gas dynamic experiments on dense organic flows in order to validate numerical codes. The second TS is a test-bench for mini-ORC expanders of any configuration up to a power output of 100 kWe. This paper presents the preliminary design of the ORCHID setup, discussing how the required operational flexibility was attained. The envisaged experiments of the two TS’s are also described.

Microturbine performance and losses are strongly dependent on scale, especially at very small sizes. As a consequence, prediction of these scale effects is important within the framework of conceptual design and sizing studies where the power output is varied in order to optimize the application in which the microturbine is integrated. The scale effects can be addressed for the individual gas path and mechanical components which include turbomachinery, ducting, bearings, recuperators, combustors etc. Absolute prediction of efficiencies at the initial design stage, or at any other stage, is difficult, and the designer usually relies upon empirical loss models and correlations. Using both empirical and physical analysis, these relations can be extended to include size as a variable providing a means to predict changes of losses relative to a known reference case. This paper describes the results from an analysis of size-related loss mechanisms in small turbomachinery derived from turbochargers. A microturbine cycle performance analysis is presented in order to illuminate how these effects influence efficiency at varying design power levels. In addition, geometric size and weight relations are derived for prediction of physical dimensions as a function of design power. A case study is presented scaling microturbine concepts in the range of 10–36kW for an electric vehicle range extender application.

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