The efficient conversion of solar radiation into heat at high temperature levels requires the use of concentrating solar collectors. The goal of this paper is to present the optical and the thermal analysis of a parabolic dish concentrator with a spiral coil receiver. The parabolic dish reflector consists of 11 curvilinear trapezoidal reflective petals constructed by PMMA with silvered mirror layer and has a diameter of 3.8 m, while its focal distance is 2.26m. This collector is designed with commercial software SolidWorks and simulated, optically and thermally in its Flow Simulation Studio. The optical analysis proved that the ideal position of the absorber is at 2.1m from the reflector in order to maximize the optical efficiency and to create a relative uniform heat flux over the absorber. In thermal part of the analysis, the energetic efficiency was calculated approximately 65%, while the exergetic efficiency is varied from 4% to 15% according to the water inlet temperature. Moreover, other important parameters as the heat flux and temperature distribution over the absorber are presented. The pressure drop of the absorber coil is calculated at 0.07bar, an acceptable value.

In this study, the optical design of a solar parabolic dish concentrator is presented. The parabolic dish concentrator consists from 11 curvilinear trapezoidal reflective petals made of polymethyl methacrylate with special reflective coating. The dish diameter is equal to 3.8 m and the theoretical focal point distance is 2.26 m. Numerical simulations are made with the commercial software TracePro from Lambda Research, USA, and the final optimum position between absorber and reflector was calculated to 2.075 m; lower than focus distance. This paper presents results for the optimum position and the optimum diameter of the receiver. The decision for selecting these parameters is based on the calculation of the total flux over the flat and corrugated pipe receiver surface; in its central region and in the peripheral region. The simulation results could be useful reference for designing and optimizing of solar parabolic dish concentrators as for as for CFD analysis, heat transfer and fluid flow analysis in corrugated spiral heat absorbers. [Projekat Ministarstva nauke Republike Srbije, br. III42006: Research and development of energy and environmentally highly effective polygeneration systems based on renewable energy resources i br. III45016: Fabrication and characterization of nanophotonic functional structures in biomedicine and informatics]

Solar energy may be practically utilized directly through transformation into heat, electrical or chemical energy. We present a procedure to design a square facet concentrator for laboratory-scale research on medium-temperature thermal processes. The efficient conversion of solar radiation into heat at these temperature levels requires the use of concentrating solar collectors. Large concentrating dishes generally have a reflecting surface made up of a number of individual mirror panels (facets). Optical ray tracing is used to generate a system performance model. A square facet parabolic solar concentrator with realistic specularly surface and facet positioning accuracy will deliver up to 13.604 kW of radiative power over a 250 mm radius disk (receiver diameter) located in the focal plane on the focal length of 1500 mm with average concentrating ratio exceeding 1200. The Monte Carlo ray tracing method is used for analysis of the optical performance of the concentrator and to identify the set of geometric concentrator parameters that allow for flux characteristics suitable for medium and high-temperature applications.

The use of solar dish thermal collectors is a promising choice for designing sustainable energy systems. The use of nanofluids is a new way for enhancing the thermal performance of solar collectors because of their improved thermal properties. The objective of this study is to investigate the use of mono and hybrid nanofluids in a solar dish collector in order to determine which kind of nanofluids leads to higher performance enhancements. The analysis is conducted with a developed thermal model in Engineering Equation Solver and the collector is studied thermally and exergetically. The examined hybrid nanofluid has as base fluid syltherm 800 with 1% Cu and 1% TiO 2. Moreover, the examined mono nanofluids are the syltherm 800 with 2% Cu and syltherm 800 with 2% TiO 2. The investigated solar dish collector has a spiral absorber and it is examined for inlet temperatures from 25 °C up to 300 °C with a flow rate of 200 L/h. According to the final results, the use of hybrid nanofluid leads to higher thermal efficiency enhancement compared to the mono nanofluids because of the higher increase in the Nusselt number in the flow. More specifically, the use of the hybrid nanofluids leads to 0.99% mean thermal efficiency enhancement compared to the pure oil case, while the use of Oil/Cu and Oil/TiO 2 lead to 0.42% and to 0.56% mean thermal efficiency enhancement, respectively. Moreover, the exergy efficiency is found enhanced with the use of all nanofluids. The mean exergy efficiency enhancement is 1.21% with the hybrid nanofluid, while it is 0.73% with Oil/TiO 2 and 0.53% with Oil/Cu.

Solar energy exploitation is one of the most promising techniques for achieving the sustainability in the energy domain. The objective of this work is to investigate the daily performance of a solar dish collector under different operating temperature levels. A solar dish collector with 10.28 m 2 aperture and a spiral coil absorber is investigated. The analysis is performed with a developed numerical model in engineering equation solver which has been validated with experimental results. The analysis proved that the daily thermal efficiency of the collector is ranged from 67.36% to 54.65% for inlet temperatures from 50 °C to 350 °C, respectively. On the other hand, the exergy efficiency presents an increasing rate of the inlet temperature and it is found to be ranged from 8.77% up to 31.07% for the respective temperatures. The daily exergy production of the collector can reach up to 26 kWh with a respective thermal production of 50 kWh for inlet temperature equal to 350 °C. The results of this work can be exploited for the suitable evaluation of the solar dish collector on a daily basis.