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The use of organic refrigerants or supercritical CO2 (sCO2) as a working fluid in closed loop power cycles has the potential to revolutionise power generation. Thermodynamic cycle efficiency can be improved by selecting bespoke working fluids that best suit a given combination of heat source and heat sink temperatures, but thermal efficiency can be maximised by pairing this with a custom made turbine. This work describes the development and design of a new 100kW thermal laboratory-scale test loop at the University of Queensland. The loop has capabilities for characterising both simple and recuperated refrigerant and sCO2 organic Rankine cycles in relation to overall cycle performance and for the experimental characterisation of radial inflow turbines. The aim of this facility is to generate high quality validation data and to gain new insight into overall loop performance, control operation, and loss mechanisms that prevail in all loop components, including radial turbines when operating with supercritical fluids. The paper describes the current test loop and provides details on the available test modes: an organic Rankine cycle mode, a closed loop Brayton cycle mode, and heat exchanger test mode and their respective operating ranges. The bespoke control and data acquisition system has been designed to ensure safe loop operation and shut down and to provide high quality measurement of signals from more than 60 sensors within the loop and test turbine. For each measurement, details of the uncertainty quantification in accordance with ASME standards are provided, ensuring data quality. Data from the commissioning of the facility is provided in this paper. This data confirms controlled operation of the loop and the ability to conduct both cycle characterisation tests and turbomachinery tests.

The aim of this thesis is to develop a methodology to model and simulate the dynamics of Organic Rankine Cycle (ORC) power plants, and to demonstrate and validate this methodology by performing experiments on a laboratory-scale ORC plant. Typical plant models for ORCs provide steady state analysis of thermodynamic cycles and losses, but for a system that has complex starting mechanisms and undergoes fluctuations in operating conditions due to environmental effects, dynamic models are needed to predict how the system will behave. Two main questions are interesting to an ORC designer. What is the start-up and shut-down time of the plant? And: What effect does an unprecedented slow or sharp transient in one or multiple physical variables have on the system? There are a number of modelling libraries available for the simulation of Rankine cycles, however there is no complete package that covers all potential dynamic scenarios and is fully documented with guidance on how to develop a stable dynamic model. Issues such as component selection and parameterisation criteria, compilation of stable models in large systems, simulation initialisation strategies, and heat transfer model selection present many challenges to the inexperienced modeller. This thesis aims to address these issues and document strategies to overcome them.Existing modelling libraries do not include extensive heat transfer models that can accurately simulate the heat exchange that occurs during dynamic transients in ORC heat exchangers. Void fraction is a critical variable for the dynamics of a closed thermodynamic cycle that depends on accurate heat transfer models, and models that switch between single-phase and two-phase heat transfer correlation are beneficial here. Development of an extension of the existing heat transfer models to better model these effects is another aim of this thesis.A smaller ORC laboratory that is separate to the main facility used in this project was available early in the thesis to test initial heat exchanger and cycle modelling results. An intermediate project goal was to use this laboratory to model and analyse a novel small-scale solar cogeneration unit that uses cheap and available components to heat water and produce power using a scroll expander. The completion of this goal was seen as a fundamental step toward understanding the physical characteristics of an ORC that is producing power, and to observe the system dynamics. The results of i the study include a typical day's power output for various times of the year, and show the competitiveness of this type of system.The major contributions that originate from the main body of work on the larger ORC facility are:• Development of extended pipe models that include an extra wall for heat transfer to a shell or the environment;• Development of detailed, deterministic plate heat exchanger models with descriptive parameters that can be quickly configured by an inexperienced modeller. These include extensions to heat transfer models and a new phase switching method ...

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