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Broad-band absorbers are very important for solar thermal utilization. However, seeking ideal solar absorbers whose absorption spectra match well with the solar spectrum is still a great challenge. In this work, zirconium carbide (ZrC) nanofluids with broad-band absorption characteristic were prepared by milling and dispersing ZrC nanoparticles in water. The ZrC nanoparticles show strong optical absorption in the range from 300 to 2000 nm. At a penetration distance of 1 cm, the ZrC nanofluids of 0.02 wt% can absorb almost 100% of the solar irradiation in the full spectrum and the solar weighted absorption coefficient (Am) is 0.99. The results indicate that the ZrC nanofluids of 0.02 wt% are very close to the ideal solar irradiation absorbers. The photo-thermal conversion efficiency of the ZrC nanofluids was evaluated by a direct method focusing on the nanofluids themselves instead of indirectly represented by the efficiency of the solar thermal collector as presented in the previous reports. By recording and analyzing the temperature rise of the nanofluids under the illumination of a solar simulator, the photo-thermal conversion efficiency for the ZrC nanofluids of 0.02 wt% was determined to be 92%. The high efficiency is attributed to the broad-band absorption of the ZrC nanoparticles.

Nanofluid is a new class of heat transfer fluids containing nano-sized particles, fibers, or tubes that are stably suspended in a carrier liquid. In this article, carbon black nanofluids were prepared by dispersing the pre-treated carbon black powder into ethylene glycol. The thermal conductivities, rheological behaviors and photo-thermal properties of the nanofluids were investigated. The results showed that the thermal conductivities of carbon black nanofluids increased with particle loading and temperature. The nanofluids performed a shear thinning behavior. The shear viscosity increased with particle loading while decreased with temperature at the same shear rate. Carbon black nanofluids had good absorption ability of solar energy and could effectively enhance the solar absorption efficiency.

Nanofluid is a new class of heat transfer fluids containing nano-sized particles, fibers, or tubes that are stably suspended in a carrier liquid. In this article, carbon black nanofluids were prepared by dispersing the pre-treated carbon black powder into ethylene glycol. The thermal conductivities, rheological behaviors and photo-thermal properties of the nanofluids were investigated. The results showed that the thermal conductivities of carbon black nanofluids increased with particle loading and temperature. The nanofluids performed a shear thinning behavior. The shear viscosity increased with particle loading while decreased with temperature at the same shear rate. Carbon black nanofluids had good absorption ability of solar energy and could effectively enhance the solar absorption efficiency. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of MRS-Taiwan

In the current paper, we report the synthesis of spherical and cubic copper sulfide hollow structures, as well as the influence of shape and thickness on the photo-thermal conversion of the as-synthesized products. Copper sulfide hollow structures of different thickness were synthesized base on a sacrificial template strategy using spherical and cubic Cu2O precursors as templates. Optical absorption of the as-synthesized products was investigated with UV-Vis spectrometer. Photo-thermal conversion property was studied with a lab-made evaluation system equipped with an AUT-FSL semiconductor/solid state laser. The results indicate that the as-prepared products exhibited significant absorption in visible light regions. Under the irradiation of laser beam with a wavelength at 635 nm and a power of 0.015 W, the temperature elevations of the aqueous suspensions containing 0.24% mass fraction of spherical and cubic copper sulfide hollow structures were measured to be 5 °C and 6 °C within 60 seconds, respectively. On the contrast, water showed little temperature elevation under the same conditions.

Manganese ferrite (MnFe2O4) hollow microspheres were synthesized through a sacrificial template approach using manganese carbonate (MnCO3) microspheres as sacrificial templates. Different from the literatures, the synthesis of MnFe2O4 hollow spheres was achieved through a one-pot hydrothermal process without subsequent calcination process. The temperature and reaction time of the hydrothermal process were set to be 180 °C and 8 h. The formation mechanism of the MnFe2O4 hollow microspheres was also investigated. Results indicate that the average diameter of the as-synthesized MnFe2O4 hollow microspheres is 1.2 μm. The shells of the hollow microspheres are composed of nanoparticles. During hydrothermal process, Mn2+ ions diffused outward and resulted in shell materials of MnFe2O4, thus MnCO3 templates were consumed and MnFe2O4 hollow microspheres were obtained.

A hydrogen arc plasma method for preparing nano-particles was introduced. A method which possesses higher production rate, lower energy consumption and is suitable for preparation of nano-particles of metals with high melting point. The microstructures and properties of the nano-particles prepared by this method were reported.

Nanoscale copper and silver were synthesized by the H2+Ar arc plasma method. During the synthesis, hydrogen molecules were dissociated into hydrogen atoms and stored in the particles. At the same time, nanometer copper and silver particles were prepared by the inert gas condensation method whose power is about identical with the hydrogen arc plasma method. Various specimens were annealed respectively at low temperature. The particle size was measured by a transmission electron microscopy. A proper temperature was chosen to prepare the standard specimen.

In this article, a wet chemical method was developed to prepare stable CuO nanofluids. The influences of synthesis parameters, such as kinds and amounts of copper salts, reaction time, were studied. The thermal conductivities of CuO nanofluids were also investigated. The results showed that different copper salts resulted in different particle morphology. The concentration of copper acetate and reaction time affected the size and shape of clusters of primary nanoparticles. Nanofluids with different microstructures could be obtained by changing the synthesis parameters. The thermal conductivities of CuO nanofluids increased with the increase of particle loading.