Several heat-to-power conversion technologies are being proposed as suitable for waste-heat recovery (WHR) applications, including thermoelectric generators, hot-air (e.g., Ericsson or Stirling) engines, and vapour-cycle engines such as steam or organic Rankine cycle (ORC) power systems. The latter technology has demonstrated the highest efficiencies at small and intermediate scales and low to medium heat-source temperatures and is considered a particularly suitable option for WHR in relevant applications. However, ORC systems experience variations in performance at part-load or off-design conditions, which needs to be predicted accurately by empirical or physics-based models if one is to assess accurately the techno-economic potential of such ORC-WHR solutions.
This thesis reports on the design and construction of a small-scale (1-kWe) ORC prototype and examines its operation over a range of conditions. It presents results from a series of experimental tests and related investigations into the part-load performance of the ORC engine, operated with R245fa as a working fluid, with the aim of producing high-fidelity steady-state and transient data relating to the operational performance of this engine. The experimental apparatus is composed of a rotary-vane pump, brazed-plate evaporator and condenser, and a scroll expander with an adjustable load. An electric heater is used to provide a hot oil-stream to the evaporator, supplied at different temperatures, from 100 °C to 140 °C.
The optimal operating conditions, i.e., pump speed and expander load, are determined at various heat-source conditions and the steady-state data points used to analyse the part-load performance of the engine. A performance map is drawn that captures a component scale performance
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and the overall system performance. An exergy analysis allows us to quantify the contribution of each component to the overall exergy destruction. The data can be used for the development and validation of advanced models capable of steady-state part-load and off-design performance predictions, as well as predictions of the transient/dynamic operation of ORC systems.However, ORC systems experience variations in performance at part-load or off-design conditions, which needs to be predicted accurately by empirical or physics-based models if one is to assess accurately the techno-economic potential of such ORC-WHR solutions.
This thesis explores the design and operation of a small scale ORC. It presents results from an experimental investigation of the part-load performance of a 1-kWe ORC engine, operated with R245fa as a working fluid, with the aim of producing high-fidelity steady-state and transient data relating to the operational performance of this system.
The experimental apparatus is composed of a rotary-vane pump, brazed-plate evaporator and condenser, and a scroll expander with an adjustable load. An electric heater is used to provide a hot oil-stream to the evaporator, supplied at different temperatures: 100 through 140 °C. The optimal operating conditions, i.e., pump speed and expander load, are determined at various heat-source conditions and the steady-state data points used to analyse the part-load performance of the engine.
A performance map is drawn that captures a component scale performance and the overall system performance. An exergy analysis allows us to quantify the contribution of each component to the overall exergy destruction. The data can be used for the development and validation of advanced models capable of steady-state part-load and off-design performance predictions, as well as predictions of the transient/dynamic operation of ORC systems.