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Session: Poster session & Sponsor Exhibition
Session starts: Monday 07 October, 14:00

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Martin White ()
Abdulnaser Sayma ()

Abstract:
Despite increasing interest in ORC over recent years, small scale systems have yet to make their mark due to the lack of an efficient, ORC specific expander and high costs. However, with careful component selection and design, an efficient and economical system could see widespread use within applications such as solar power and waste heat recovery. For small outputs, volume expanders such as screw and scroll machines have typically been preferred over turbo-expanders due to lower rotational speeds and ease of conversion from compression machines. However, for 10kWe output screw devices experience high leakage flows, whilst scroll machines remain untested, and are limited in efficiency. An efficient, well designed radial expander could therefore bridge the current gap between the output of scroll and screw based cycles. This paper describes the development of a steady-state ORC sizing and optimisation tool integrated with real fluid properties. The program, implemented in FORTRAN, advances on current models by combining detailed component models, including off-design performance, with multi-objective optimisation. For a pre-defined set of components the objective function is the maximisation of work output which results in an optimal solution which couples component and system performance. Comparatively, the model can also be used for component sizing through the use of an objective function which couples performance with system complexity. A modular modelling approach allows the interchanging of different objective functions in addition to different component models. An initial case study is explored, and R-245fa or R-123 are found to be the most suitable working fluids for an experimental system. This selection is based on thermodynamic, environmental and design considerations, in addition to the practicalities of the available lab space. These results will be used to size the rig and construct a prototype expander. After model validation, more novel working fluids will be explored.