Structure and Properties of Highly Porous Alumina-Based Ceramic Materials after Heating by Concentrated Solar Radiation

Three ceramic fibrous materials of the Al2O3-SiO2 system with different densities have been treated using concentrated solar radiation. The experiment was performed using technological capabilities of the Big Solar Furnace in the 2 modes: the first mode includes heating up to 1400–1600 °C, holding for 1.5–2 h; the second mode (the fusion mode) includes heating up to 1750–1900 °C until the sample destruction, which is accompanied by fusion. Upon completion of the experiment, the phase composition, microstructure, and compressive strength of the materials were studied. It was shown that the investigated materials retained their fibrous structure under prolonged treatment in the first mode up to temperatures of 1600 °C. The phase composition of the ceramic materials changes during the experiment, and with a decrease in the density, the modification is more pronounced. Treatment of all three materials under study in the fusion mode resulted in the formation of the eutectic component in the form of spherulites. The compressive strength of the materials was found to be slightly reduced after exposure to concentrated solar radiation.

ADJUSTMENT OF LARGE SOLAR OVEN FLAT HELIOSTAT HELIOSTATS

This paper presents an improved method for adjusting individual mirrors –facets of heliostats of a Big Solar Furnace (BSF) with a heat output of 1000 kW in Uzbekistan. Due to the fact that a BSF consists of 22,790 pieces of individual mirrors, the adjustment - setting a specific geometric position of these mirrors is very important. The process of adjusting the mirrors is very time consuming and lengthy. Often exactly the adjustments are influenced by subjective factors by the aligners. In order to improve the performance and accuracy of the alignment, the facet of heliostats has applied the Technical Vision System (TVS), as well as improved the process of assessing the state of alignment and the processing of alignment data. The TVS consisting of a video camera, an interface, a personal computer and special software allows you to visually and accurately assess the alignment conditions of the heliostat facets before and after the alignment process. Allows you to save the data in computer memory for further processing and analysis. Allows you to create a database of the alignment status of each of the 62 heliostats of LSF. Special software developed by us allows you to quickly and accurately determine the deviations of the heliostat facets from the calculated geometric points in angular minutes. Based on the data obtained, you can build histograms, graphs, etc. for visual analysis of the heliostat alignment states before and after the alignment process.

Hydrogen Production in Methane Decomposition Reactor Using Solar Thermal Energy

This study investigates the decomposition of methane using solar thermal energy as a heat source. Instead of the direct thermal decomposition of the methane at a temperature of 1200 °C or higher, a catalyst coated with carbon black on a metal foam was used to lower the temperature and activation energy required for the reaction, and to increase the yield. To supply solar heat during the reaction, a reactor suitable for a solar concentrating system was developed. In this process, a direct heating type reactor with quartz was initially applied, and a number of problems were identified. An indirect heating type reactor with an insulated cavity and a rotating part was subsequently developed, followed by a thermal barrier coating application. Methane decomposition experiments were conducted in a 40 kW solar furnace at the Korea Institute of Energy Research. Conversion rates of 96.7% and 82.6% were achieved when the methane flow rate was 20 L/min and 40 L/min, respectively.

Numerical Study on Optics and Heat Transfer of Solar Reactor for Methane Thermal Decomposition

This study aims to reduce greenhouse gas emissions to the atmosphere and effectively utilize wasted resources by converting methane, the main component of biogas, into hydrogen. Therefore, a reactor was developed to decompose methane into carbon and hydrogen using solar thermal sources instead of traditional energy sources, such as coal and petroleum. The optical distributions were analyzed using TracePro, a Monte Carlo ray-tracing-based program. In addition, Fluent, a computational fluid dynamics program, was used for the heat and mass transfer, and chemical reaction. The cylindrical indirect heating reactor rotates at a constant speed to prevent damage by the heat source concentrated at the solar furnace. The inside of the reactor was filled with a porous catalyst for methane decomposition, and the outside was surrounded by insulation to reduce heat loss. The performance of the reactor, according to the cavity model, was calculated when solar heat was concentrated on the reactor surface and methane was supplied into the reactor in an environment with a solar irradiance of 700 W/m2, wind speed of 1 m/s, and outdoor temperature of 25 °C. As a result, temperature, methane mass fraction distribution, and heat loss amounts for the two cavities were obtained, and it was found that the effect on the conversion rate was largely dependent on a temperature over 1000 °C in the reactor. Moreover, the heat loss of the full-cavity model decreased by 12.5% and the methane conversion rate increased by 33.5%, compared to the semi-cavity model. In conclusion, the high-temperature environment of the reactor has a significant effect on the increase in conversion rate, with an additional effect of reducing heat loss.

Zigzag Multirod Laser Beam Merging Approach for Brighter TEM00-Mode Solar Laser Emission from a Megawatt Solar Furnace

An alternative multirod solar laser end-side-pumping concept, based on the megawatt solar furnace in France, is proposed to significantly improve the TEM00-mode solar laser output power level and its beam brightness through a novel zigzag beam merging technique. A solar flux homogenizer was used to deliver nearly the same pump power to multiple core-doped Nd:YAG laser rods within a water-cooled pump cavity through a fused silica window. Compared to the previous multibeam solar laser station concepts for the same solar furnace, the present approach can allow the production of high-power TEM00-mode solar laser beams with high beam brightness. An average of 1.06 W TEM00-mode laser power was numerically extracted from each of 1657 rods, resulting in a total of 1.8 kW. More importantly, by mounting 399 rods at a 30° angle of inclination and employing the beam merging technique, a maximum of 5.2 kW total TEM00-mode laser power was numerically extracted from 37 laser beams, averaging 141 W from each merged beam. The highest solar laser beam brightness figure of merit achieved was 148 W, corresponding to an improvement of 23 times in relation to the previous experimental record.

Characterization of Solar-Aged Porous Silicon Carbide for Concentrated Solar Power Receivers

Porous silicon carbide is a promising material for ceramic receivers in next-generation concentrated solar power receivers. To investigate its tolerance to thermal shock, accelerated ageing of large coupons (50 × 50 × 5 mm) was conducted in a solar furnace to investigate the effects of thermal cycling up to 1000 °C, with gradients of up to 22 °C/mm. Non-destructive characterization by computed X-ray tomography and ultrasonic inspection could detect cracking from thermal stresses, and this informed the preparation of valid specimens for thermophysical characterization. The effect of thermal ageing on transient thermal properties, as a function of temperature, was investigated by using the light-flash method. The thermophysical properties were affected by increasing the severity of the ageing conditions; thermal diffusivity decreased by up to 10% and specific heat by up to 5%.

Approaches to Simulation of Interaction of Concentrated Solar Radiation with Materials

The paper analyzes approaches to modeling the processes of interaction of concentrated solar radiation with materials. The experimental results obtained on the synthesis of materials from a melt in a solar furnace are presented. It is shown that when melting in a solar furnace under the influence of concentrated solar radiation of high density due to the acceleration of the recovery process, it is possible to obtain a fine-grained microstructure that gives the material enhanced mechanical and dielectric properties. It is shown that the relationship between the structure and properties of the materials obtained with the technological parameters of melting and cooling in a solar furnace can be used as an approach to modeling the interaction of concentrated solar radiation with materials

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

Using a high-flux solar furnace, loosely compacted powders of Va-group transition metal (V, Nb, and Ta) were reacted with stream of NH3 gas (uncracked NH3 gas) being heated by concentrated solar beam to a temperature (T) range between 600 and 1000 °C. From V, sub-nitride V2N (γ phase) and hypo-stoichiometric mono-nitride VN possessing fcc (face-centered cubic) crystal lattice structure (δ phase) were synthesized. On the other hand, in the reaction product from Nb and Ta, hexagonal mono-nitride phase with N/M atom ratio close to 1 (ε phase) was detected. The reaction duration was normalized to be 60 min. In a conventional industrial or laboratory electric furnace, the synthesis of mono-nitride phase with high degree of crystallinity that yield sharp XRD peaks for Va-group metal might take a quite long duration even at T exceeding 1000 °C. In contrast, mono–nitride phase MN of Va-group metal was synthesized for a relatively short duration of 60 min at T lower than 1000 °C being co-existed with lower nitride phases.