Mostrando artículos por etiqueta: Renewable Energy
Comments to “A simple method to achieve a uniform flux distribution in a multi-faceted point focus concentrator”
Lúar Moreno-Álvarez, Andrés Amat-Castrillón
Abstract
We have found the flux homogenization technique described in the paper published in volume 93, pages 115–124 (august 2016), does not provide homogenized fluxes in all out-of-focus distances of the solar receiver, but only above a certain transition distance, and that some of the numerical analysis procedures used in that document should be revised or complemented to achieve better reproducibility of the results. In addition, we also note that some statements and conclusions in that document are mistaken or formulated incorrectly, so it is necessary their correction.
Thermal analysis of a finned receiver for a central tower solar system
A Piña-Ortiz, JF Hinojosa, RA Pérez-Enciso, VM Maytorena, RA Calleja, CA Estrada
Abstract
In this study, a thermal analysis of a finned receiver prototype for a thermosolar tower system is presented. The experimental system consists of parallelepiped aluminum enclosure of 1.2 m high, 1.23 m wide and 0.1 m depth. At the interior, 1232 cylindrical fins with a diameter of 0.0095 m (3/8”) and 0.09 m length increases the heat transfer area up to 225%. The vertical wall receives the incoming solar concentrated radiation from a group of heliostats whilst at the interior a constant flow of water removes the absorbed energy. Experimental temperature profiles were obtained at different heights and depths and a comparison was made with numerical results obtained with the use of commercial CFD software. It was found that the maximum thermal efficiency of the receiver was 94.4 %, decreasing as the radiative flux increases.
Thermal analysis of a finned receiver for a central tower solar system
Experimental aspects of CuO reduction in solar-driven reactors: Comparative performance of a rotary kiln and a packed-bed
Elisa Alonso, Carlos Pérez-Rábago, Javier Licurgo, Alessandro Gallo, Edward Fuentealba, Claudio A. Estrada
Abstract
Solar reactors designed and constructed for thermochemical applications present different configurations and general performance. The selection of a solar reactor that optimizes a particular process is always a difficult challenge. This work studies two types of reactor configuration by means of a comparative experimental analysis. It was employed a solar device, which is able to operate as fixed reactor with packed bed samples and as rotary kiln. The reduction of CuO into Cu2O was tested under both operation modes, due to its proved potential and interest as thermochemical storage material. It was found that heat transfer was hindered in static experiments limiting the fraction of reactive sample. Thermal gradients of about 200 °C were found in the packed bed through thermocouple and IR camera measurement. Heating rates and total fed energy must be restricted at the risk of front of the sample to melt, resulting in several operation drawbacks. In contrast, mixing conditions in rotary kilns allowed for higher heating rates and led to homogenous sample temperature. Maximum reaction yields in stationary mode did not overpass 14% while it was achieved more than 80% in rotary mode at temperatures about 860 °C. Thermal efficiencies were very limited in both operation modes due to the high thermal inertia of the solar reactor. Because rotary mode admitted much more energy, its thermal efficiency was even lower than static. A solution to increase rotary kilns thermal efficiency is working in continuous mode.
A simple method to achieve a uniform flux distribution in a multi-faceted point focus concentrator
Ricardo Pérez-Enciso, Alessandro Gallo, David Riveros-Rosas, Edward Fuentealba-Vidal, Carlos Pérez-Rábago
Abstract
A method to achieve a uniform flux distribution with a multi-faceted point focus concentrator for laboratory tests is proposed in this work. The method can be applied to different types of receiver - thermal or photovoltaic - and no additional device is required to homogenize the flux. The technique consists in moving the receiver from the focal plane and enlarging the solar spot impinging on it. At the same time, each mirror aim-point is adjusted in order to superimpose the images that have been generated by every facet. To evaluate the method, a real multi-faceted concentrator composed of eighteen spherical mirrors was modeled in a ray-tracing software. The procedure was validated through the comparison of an image of the real solar spot on the receiver generated by three mirrors, and the simulated flux obtained the same way. This way a mean concentrator global optical error of 2.8 mrad was estimated. This value was used then for further analyses. Results show that the concentration factor can be varied in a range of 150–900 suns over a receiver diameter of up to 7 cm. Hence, according to the receiver requirements, it is possible to expand the distribution and to alter the intensity of the flux. Finally, optical parametrical analyses were carried out, from which it is inferred that good quality optics give rise to a more homogeneous solar flux on the receiver.
A simple method to achieve a uniform flux distribution in a multi-faceted point focus concentrator
Influence of the Size of Facets on Point Focus Solar Concentrators
D. Riveros-Rosas, M. Sánchez-González, C. A. Arancibia-Bulnes, C. A. Estrada.
Abstract
It is a common practice in the development of point focus solar concentrators to use multiple identical reflecting facets, as a practical and economic alternative for the design and construction of large systems. This kind of systems behaves in a different manner than continuous paraboloidal concentrators. A theoretical study is carried out to understand the effect of the size of facets and of their optical errors in multiple facet point focus solar concentrating systems. For this purpose, a ray tracing program was developed based on the convolution technique, in which the brightness distribution of the sun and the optical errors of the reflecting surfaces are considered. The study shows that both the peak of concentration and the optimal focal distance of the system strongly depend on the size of the facets, and on their optical errors. These results are useful to help concentrator developers to have a better understanding of the relationship between manufacturing design restrictions and final optical behavior.
Influence of the Size of Facets on Point Focus Solar Concentrators