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Both single-walled and multi-walled carbon nanotubes (SWNTs and MWNTs) are produced using a solar reactor working under nitrogen atmosphere. Samples were studied by transmission electron microscopy (TEM), Raman spectroscopy and electron energy loss spectroscopy (EELS). The produced MWNTs exhibit the typical morphologies observed for nitrogen-doped MWNTs synthesized with other methods and EELS measurements point out the presence of substituted nitrogen within the tubes. The doping level is not uniform and the maximum value reaches 11 at.%. [ABSTRACT FROM AUTHOR]

Presents information on a study which discussed the solar processing of materials with respect to laser or plasma systems. Classification of solar energy as applied in the field of chemistry; Details on the experiment based on three domains; Conclusion.

Abstract: The solar thermochemical decomposition of CH4 is carried out in a solar reactor consisting of a cavity-receiver containing an array of tubular absorbers, through which CH4 flows and thermally decomposes to H2 and carbon particles. A reactor model is formulated by coupling radiation/convection/conduction heat transfer and chemical kinetics for a two-phase solid-gas reacting flow. Experimental validation is accomplished by comparing measured and simulated absorber temperatures and H2 concentrations for a 10 kW prototype reactor tested in a solar furnace. The model is applied to optimize the design and simulate the performance of a 10 MW commercial-scale reactor mounted on a solar tower system configuration. Complete conversion is predicted for a maximum CH4 mass flow rate of 0.70 kg s−1 and a desired outlet temperature of 1870 K, yielding a solar-to-chemical energy conversion efficiency of 42% and a solar-to-thermal energy conversion efficiency of 75%. [ABSTRACT FROM AUTHOR]

Previous studies proved the Dense Particle Suspension (DPS) - also called Upward Bubbling Fluidized Bed (UBFB) - could be used as Heat Transfer Fluid (HTF) in a single-tube solar receiver. This article describes the experiments conducted on a 16-tube, 150 kW th solar receiver using a dense gas-particle suspension (around 30% solid volume fraction) flowing upward as HTF. The receiver was part of a whole pilot setup that allowed the continuous closed-loop circulation of the SiC particles used as HTF. One hundred hours of on-sun tests were performed at the CNRS 1 MW solar furnace in Odeillo. The pilot was tested under various ranges of operating parameters: solid mass flow rate (660–1760 kg/h), input solar power (60–142 kW), and particle temperature before entering the solar receiver (40–180 °C). Steady states were reached during the experiments, with continuous circulation and constant particle temperatures. For the hottest case, the mean particle temperature reached 430 °C in the collector fluidized bed, at the receiver outlet, and it went up to 700 °C at the outlet of the hottest tube, during steady operation. A temperature difference between tubes is observed that is mainly due to the incident solar flux distribution heterogeneity. The thermal efficiency of the receiver, defined as the ratio of power transmitted to the DPS in the form of heat over solar power entering the receiver cavity, was calculated in the range 50–90% for all the experimental cases. The system transient responses to variations of the solar irradiation and of the solid mass flow rate are also reported. [ABSTRACT FROM AUTHOR]

Volumetric absorbers appear to be a promising technology in order to heat air above 1000 °C to feed combined-cycles (Brayton and Rankine thermodynamic cycles in cascade) for solar thermal electricity production. Thus, the choice of the absorber characteristics (material, geometrical parameters) is the key parameter to reach a maximum solar-to-thermal energy conversion efficiency. In this study, a test bench was developed and the solar-to-thermal efficiency of reticulate porous ceramics with open pores was characterized. Improvements with current state-of-the-art were made by the use of a homogenizer, ensuring spatially homogenized concentrated solar flux irradiation. Fluxmetry and calorimetry measurements were realized to evaluate the flux map incident on the tested absorber samples. A co-current position for the solar incoming power and the air flow rate was chosen for future comparisons with numerical predictions of atmospheric volumetric receivers. Several foam samples currently available in the industry were tested (Silicon Carbide, SiC) covering a wide range of porosity (72–92%) and pores per inch (5–20). A new selective material was also investigated (Zirconium Diboride, ZrB 2 ). Experimental results for random foams were compared to the SiC honeycomb absorber considered to be the reference volumetric receiver. In the literature, two trends were proposed to produce the best performances: (1) the use of foams with large pore diameters and high porosity and (2) the use of small pore diameters with low porosity. This study showed the second trend resulted in the best absorber efficiency. In addition, the use of selective materials was found promising for atmospheric air receiver, provided the solar absorptivity and the durability could be controlled. [ABSTRACT FROM AUTHOR]