Computer Modelling of the Optical Behavior of Homogenizers in High-Flux Solar Furnaces

Abstract

Solar radiation homogenizers are multi-mirror devices that try to reshape the solar radiation distribution coming from a concentrator, so that, after passing through the homogenizer, the light flux becomes as much evenly distributed as possible. The optical behavior of these multi-reflective devices is complex and still ill-understood. The geometry of the concentrator defines the features of the concentrated flux and then the characteristics of a particular homogenizer must be chosen according to the envisaged use. In this work, we developed and used optical ray-tracing software to investigate how the homogenizer’s optical output is affected by the following homogenizer’s characteristics: (i) Number of reflecting surfaces; (ii) total length; (iii) position (relative to focal plane); and (iv) tilt angle (inclination) of reflecting surfaces. The obtained results provide valuable information for the use of these optical devices and may contribute to the development of more efficient strategies for homogenization of concentrated radiation generated by high-flux solar furnaces.

Experimental Validation of Double Paraboloid Reflection for Obtaining Quasi-Homogeneous Distribution of Concentrated Solar Flux

“…The statistical results obtained in this work can be compared with those obtained in previous experimental [18] and modelling [8] studies involving multi-faceted homogenisers. The decrease in the CV (standard deviation/mean value) of the measured radiation flux seems to be similar for both types of devices.…”

“…Searching for the true optical centre by moving the secondary reflector in the XY plane yields a more centred distribution of the radiation flux, as measured through the centre distance to the highest value of the radiation flux, with correspondingly higher homogeneity (lower CV for Figure 10c, as presented in Table 6). The statistical results obtained in this work can be compared with those obtained in previous experimental [18] and modelling [8] studies involving multi-faceted homogenisers. The decrease in the CV (standard deviation/mean value) of the measured radiation flux seems to be similar for both types of devices.…”

“…Most of them consist of multi-reflective devices (with mirrored sides) designed to reshape the solar radiation flux coming from a concentrator so that, after passing through the homogeniser, the flux becomes as much evenly distributed as possible. For construction reasons, homogenisers used in high-flux solar furnaces should be simple, with flat reflective surfaces or a cylinder mirrored inside and an optical behaviour similar to a symmetric polygon with infinite faces [8]. However, multi-reflection radiation homogenisers are prone to be easily damaged at high temperatures and their degree of success achieved is just satisfactory [8].…”

“…For construction reasons, homogenisers used in high-flux solar furnaces should be simple, with flat reflective surfaces or a cylinder mirrored inside and an optical behaviour similar to a symmetric polygon with infinite faces [8]. However, multi-reflection radiation homogenisers are prone to be easily damaged at high temperatures and their degree of success achieved is just satisfactory [8]. It seems fair to say that, although multi-reflection homogenisers are a reasonable workaround to solve an important difficulty in high-flux solar furnaces, they are not a robust, solid solution for the problem, and it would be highly desirable for the industry to find a better solution.…”

Synthesis of Non-Cubic Nitride Phases of Va-Group Metals (V, Nb, and Ta) from Metal Powders in Stream of NH3 Gas under Concentrated Solar Radiation

“…Temperature difference among the 8 K-type thermocouples (TC Ltd., Uxbridge, U.K.) fell in the range of ±10 °C (at 600 °C); ±20 °C (at 800 °C) and ±25 °C (at 1000 °C) throughout the test runs performed for 60 min at each set temperature. (Further information about the optical behavior of homogenisers used in high-flux solar furnaces can be found in [16]). Specifications of the reagents used in the present work are listed in Table 1.…”