In questo contesto, questa tesi riporta i risultati dell'applicazione di due innovativi ricevitori in un prototipo di concentratore parabolico asimmetrico installato nel Laboratorio di conversione dell'energia solare del Dipartimento di Ingegneria Industriale dell'Università degli Studi di Padova. La corretta progettazione del ricevitore, considerato il cuore di ogni collettore a concentrazione, è essenziale per il futuro incremento dell'efficienza di conversione di questa tecnologia. Si prevede un significativo sviluppo tecnologico per questa tipologia di collettori, a condizione che la conversione dell'energia solare diventi più efficiente ed economica. I collettori solari termici a concentrazione per media temperatura ben si prestano per l’impiego in molte applicazioni commerciali e industriali, come per la produzione di calore di processo industriale, il solar-cooling e la desalinizzazione dell'acqua di mare. La conversione dell'energia solare in calore a media temperatura (tra 80 ☌ e 250 ☌) ha recentemente riscontrato un rinnovato interesse per le applicazioni di riscaldamento e raffreddamento in settori industriali, commerciali, residenziali e dei servizi. presso il Dipartimento di Ingegneria Industriale dell'Università degli Studi di Padova. La presente tesi è il risultato del lavoro svolto durante i tre anni di dottorato. The nanofluid was tested in several conditions, with and without circulation, to investigate its stability with time. The capability of the nanofluid in collecting solar radiation when exposed to concentrated and non-concentrated solar flux are experimentally investigated thanks to the cooperation with National Council of the Research (CNR), that provided the aqueous solution. The volumetric receiver has been designed through the development of a three-dimensional computational fluid dynamics model for its installation in the focus region of the asymmetrical parabolic trough. Finally, in Chapter 5 a new direct absorption receiver is proposed to investigate the capability of a suspension of single-wall carbon nanohorns in distilled water to absorb concentrated sunlight. In Chapter 4, this model is used to evaluate the performance of a small solar-powered ORC system by coupling the aforementioned concentrating solar system with direct vaporization of a low-GWP halogenated fluid or by using an intermediate solar circuit to heat pressurized water and evaporate the same organic working fluid in a separate heat exchanger.
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A numerical model to predict its performance has been developed and validated against the experimental data. In Chapter 3, an innovative flat aluminium absorber manufactured with the bar-and-plate technology, including an internal turbulator, is tested in the asymmetrical parabolic trough collector under single-phase and two-phase flow regimes. As a result, a statistical ray-tracing model of the concentrator for optical performance analysis in different working conditions is validated and used to optimize the design of the proposed receivers. In Chapter 2, the optical performance of the asymmetrical parabolic trough is experimentally characterized. A detailed analysis of the instrumentation and of the measuring technique as well as the expression of the experimental uncertainty is provided. The study includes an indirect evaluation from measurements of global and diffuse horizontal irradiances and the use of semi-physical/empirical models. In Chapter 1, a study on different estimation procedures for the assessment of the direct normal irradiance, which is the solar resource utilized by solar concentrators, is presented. In this context, the present thesis investigates the application of two innovative concepts of receivers in a prototype of an asymmetrical parabolic trough concentrator installed in the Solar Energy Conversion Lab of the Industrial Engineering Department, at the University of Padova. The proper design of the receiver, which is considered the heart of any concentrating collector, is essential to the future improvement in the conversion efficiency of this technology. It is expected that in the future, a significant technological development can be achieved for these collectors, provided that the conversion of solar energy becomes more efficient and cost-effective. Concentrating solar thermal collectors at medium temperature are suitable for many commercial and industrial applications, such as industrial process heat, solar cooling and desalination of the seawater.
![soltrace ls3 soltrace ls3](https://ars.els-cdn.com/content/image/1-s2.0-S0038092X1830731X-gr15.jpg)
The conversion of solar energy into heat in the medium-temperature range (between 80 ☌ and 250 ☌) has recently encountered a renewed interest in heating and cooling applications of industrial, commercial, residential and service sectors.
![soltrace ls3 soltrace ls3](https://www.nrel.gov/csp/assets/images/screenshot-soltrace.jpg)
at the Department of Industrial Engineering of the University of Padova. This thesis is the results of the work conducted during the three years of Ph.D.