Omar Álvareza, Armando Rojas, Arturo Barba, Camilo A. Arancibia, Jorge Álvarez, Dulce V. Melo, Carlos E. Arreola

Abstract

This study investigates the phase transformations that can occur in an austenitic stainless steel (AISI 316) by demonstrating the appearance of δ-ferrite that is obtained in the initial heating cycles using Concentrated Solar Irradiation (CSI) at magnitudes needed to obtain the operational temperatures of central tower systems. Four AISI 316 stainless steel specimens cut from one single initial piece, were exposed to CSI in the Horno Solar de Alto Flujo Radiativo at the Universidad Nacional Autónoma de México to perform the thermal cycles. AISI 316 stainless steel is fully austenitic and is selected because it is reportedly one of the cheaper material used in CSI receivers. Monotonic tensile strength tests were performed, and it is assumed that there is no relevant effect on the mechanical behavior for the reported experiment. Phase transformations were characterized using optical microscopy, X-ray diffraction and by scanning electron microscopy analysis with an energy-dispersive X-ray spectroscopy. The appearance of δ-ferrite phase was the principal difference between CSI treated specimens, a non-treated specimen and one specimen heated by conventional method. Concentrated UV irradiation from the solar spectrum on Earth surface demonstrated to have the potential to obtain the phase transformation at a temperature near 630 °C.

Effects of concentrated solar irradiation on allotropic transformations of AISI 316 stainless steel

Publicado en Revistas Arbitradas

C. Iriarte-Cornejo, C.A. Arancibia-Bulnes, J.F. Hinojosa, Manuel I. Peña-Cruz

Abstract

The optical characteristics of solar concentrators are key factors influencing the overall efficiency of solar power plants. For instance, heliostats need to be evaluated prior to installation and during its operation lifetime. This guarantees that the optical and thermal performance of these systems is close to design. One methodology that has gained importance due to its potential capabilities has been the Fringe Reflection Technique. This technique uses the reflection of a series of regular stripes to obtain the local slope deviations from a specular surface. Coupled to a ray tracing analysis, these slopes can be used to identify the distortion in concentrated solar spots. The enormous amount of data needed to carry out this analysis difficult its implementation at large scale. In this work, a study for determining the optimal number of sample points for heliostat surface characterization is realized. It has been found that, depending on the level of errors, the number SPFS required to reach convergence in the flux distribution profiles and intercept factors is variable. However, for the wide range of parameters considered in all cases 48 SPFS where enough to reach convergences to 1%. This is equivalent to one point per every 2.5cm of facet side length. For values of slope and canting errors up to 2mrad, half this density is sufficient.

Effect of spatial resolution of heliostat surface characterization on its concentrated heat flux distribution

Publicado en Revistas Arbitradas

E Anguera, CA Estrada

Abstract

In this paper, we present two statistical methods to quantify the heterogeneity of the irradiance flux distribution, in a Concentrator Photovoltaic (CPV) dense-array, based on its operation and the optimization of current-matching. Preventing non-uniform flux distribution from design avoids the generation of hot spots, current mismatch and increases the overall efficiency of the system. This new approach considers the effects of the lowest irradiance values in the performance of the complete array, and its performance was corroborated by the simulations of a CPV array modelled in Matlab/Simulink; the irradiance distribution data as an input parameter was obtained from the images taken in a homogenization experiment, in the HoSIER, an 18,000 X solar furnace. The results are interpreted through the new concept of photovoltaic homogeneity, proven that the methodology successfully predicts the flux distributions, which enhances the efficiency of a series connected CPV array. Additionally, we found that the proposed methodology can also be used to optimize the electrical performance of dense-array CPV systems, working under the effects of non-uniformity illumination by rewiring the series connections into series-parallel configurations.

A new approach for evaluating flux uniformity for dense array concentrator photovoltaic cells

Publicado en Revistas Arbitradas

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

Publicado en Revistas Arbitradas

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