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Electronic theses and dissertations repository


Tesi etd-01092017-161721

Thesis type
Tesi di dottorato di ricerca
Analysis and design of devices for medium temperature solar thermal energy conversion
Settore scientifico disciplinare
Corso di studi
tutor Prof. Desideri, Umberto
correlatore Prof. Martorano, Luigi
correlatore Dott. Antonelli, Marco
commissario Prof. Franco, Alessandro
commissario Prof. Lemort, Vincent
commissario Prof. Micheli, Diego
Parole chiave
  • solar energy; CPC; ORC; Wankel; volumetric expansi
  • CFD; Expander devices
  • Lumped parameter approach
Data inizio appello
Riassunto analitico
The growth of energetic consumptions as well as the increase of the prices of fossil fuels and the need to reduce polluttant emissions require to develop the use of renewable sources, that may be employed in micro-generation systems.
At the moment, the components which can be employed in those applications still need a large effort to increase their performances, their efficiencies and to reduce their costs.
In this work the components involved in a solar ORC thermodynamic plant for micro generation uses were investigated. As a matter of fact, the main aim of this research was the analysis of the effects that geometric parameters or construction characteristics as well as operating conditions introduce in the performances of a number of devices used in solar thermodynamic plants based on ORC technology.
In particular typical components of this application such as pumps, condensers and heat exchangers have already been developed and much of work has been already done, while for other devices such as solar collectors and volumetric expander, as suggested by an analysis of the state of the art, there is the need to deepen their behaviour and to improve their performances. As consequence the research was conducted on a compound parabolic collector (CPC) with evacuated pipe to investigate the device for the collection of solar energy and a steam expander, obtained from a Wankel engine, to consider the device employed in the conversion of the enthalpy of the steam flow. Several methodologies, based on numerical analysis as well as experimental tests, were performed to investigate both devices.
In particular, the solar collector with evacuated pipe was first analyzed by means of a numerical model to investigate its transient behaviour and then a CFD model was developed to understand the heat transfer mechanism inside the enclosure when the evacuated pipe is not present. In this context, several CFD studies were focused to investigate the thermal influence due to the housing of several concentrators in a panel, considering also the presence of an external barrier and the truncation of the concentrators. In the end, a series of low cost technical solutions were shown with the aim to increase the efficiency of the collectors. The research on the collector was also completed with an experimental apparatus to evaluate the performances of a CPC concentrator with an evacuated pipe, whose results were validated by means the numerical model based on a lumped parameter approach.
The studies about the expander were done to assess the influence of the valves on the performances, combining a CFD analysis with experimental tests performed using compressed air as working fluid. The research continued with the development of a numeric model of the expander, that was calibrated with the results of the experimental tests, with the aim to evaluate friction losses as well as other ancillary losses. Nevertheless, those components can also be used separately in other applications; as a matter of fact the CPC could be employed to heat a fluid for industrial or domestic purposes or it could be used for desalination or for water chemical treatment, while the Wankel expander can be employed in other ORC systems using other renewable sources, such as biomass and geothermal fluids, or waste heat recovery.