Thermal properties of carbon black aqueous nanofluids for solar absorption

In this article, carbon black nanofluids were prepared by dispersing the pretreated carbon black powder into distilled water. The size and morphology of the nanoparticles were explored. The photothermal properties, optical properties, rheological behaviors, and thermal conductivities of the nanofluids were also investigated. The results showed that the nanofluids of high-volume fraction had better photothermal properties. Both carbon black powder and nanofluids had good absorption in the whole wavelength ranging from 200 to 2,500 nm. The nanofluids exhibited a shear thinning behavior. The shear viscosity increased with the increasing volume fraction and decreased with the increasing temperature at the same shear rate. The thermal conductivity of carbon black nanofluids increased with the increase of volume fraction and temperature. Carbon black nanofluids had good absorption ability of solar energy and can effectively enhance the solar absorption efficiency

Cobalt-based electrode materials for sodium-ion batteries

The demand for grid-scale energy storage systems has rapidly grown over recent years, to meet the requirements of structural innovation within the energy industry. Due to their inexpensive manufacturing and operating costs, and the similar electrochemical mechanism with the well-established lithium-ion batteries (LIBs), sodium ion batteries (SIBs) have been considered as an attractive candidate for grid-scale energy storage systems. A variety of cobalt-based cathode and anode materials, including cobalt oxides, cobalt chalcogenides and layered sodium cobaltates, have been synthesized and evaluated for sodium storage within the academic literature. In this article, we present a comprehensive review of the recent progress with cobalt-based electrodes (both as an anode and cathode material) used in SIBs. In detail, the electrochemical mechanisms, advantages and disadvantages, the relationship between crystalline structure and electrochemical performance and strategies to enhance the overall electrochemical performance of cobalt-based cathode and anode materials are discussed. Up to now, some cathode materials have already reached a high energy density, which is comparable to commercial LIBs. Furthermore, some cobalt-based materials can maintain a high Coulombic efficiency of over 99% with high reversible capacity during long cycling life. These encouraging results, allow such cobalt-based electrode materials to be a potential solution for grid-scale SIB systems

Preparation and thermal conductivity of CuO nanofluid via a wet chemical method

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

Necklace-like carbon nanofibers encapsulating V3S4 microspheres for ultrafast and stable potassium-ion storage

2020 The Royal Society of Chemistry. Potassium-ion batteries (PIBs) are promising candidates for scalable energy storage devices due to their low cost, high operating voltage and fast ionic conductivity in electrolyte. However, the research progress of PIBs still faces great challenges due to the lack of suitable hosts for reversible depotassiation/potassiation of large size K+, thus leading to low reversible capacity and poor cycling stability and rate capability. Herein, we have rationally designed a new necklace-like V3S4/carbon composite composed of V3S4 microspheres encapsulated in N-doped carbon nanofibers (V3S4@NCNFs) as an advanced anode for PIBs. Benefiting from the remarkable ion/electronic conductivity, fast electron transport, structural integrity upon cycling, and significant pseudocapacitance contributions, the V3S4@NCNF electrodes exhibit a high reversible capacity of 445 mA h g-1 after 300 cycles at 0.2 A g-1, a prolonged cycling stability of 245 mA h g-1 capacity retention over 1000 cycles at 2 A g-1, and an excellent rate performance of 249/202 mA h g-1 at 5/10 A g-1, which are superior to those of most reported anode materials for PIBs

Porous bowl-shaped VS 2 nanosheets/graphene composite for high-rate lithium-ion storage

Two-dimensional (2D) layered vanadium disulfide (VS2) is a promising anode material for lithium ion batteries (LIBs) due to the high theoretical capacity. However, it remains a challenge to synthesize monodispersed ultrathin VS2 nanosheets to realize the full potential. Herein, a novel solvothermal method has been developed to prepare the monodispersed bowl-shaped NH3-inserted VS2 nanosheets (VS2). The formation of such a unique structure is caused by the blocked growth of (001) or (002) crystal planes in combination with a ripening process driven by the thermodynamics. The annealing treatment in Ar/H2 creates porous monodispersed VS2 (H-VS2), which is subsequently integrated with graphene oxide to form porous monodispersed H-VS2/rGO composite coupled with a reduction process. As an anode material for LIBs, H-VS2/rGO delivers superior rate performance and longer cycle stability: a high average capacity of 868/525 mAh g−1 at a current density of 1/10 A g−1; a reversible capacity of 1177/889 mAh g−1 after 150/500 cycles at 0.2/1 A g−1. Such excellent electrochemical performance may be attributed to the increased active sites available for lithium storage, the alleviated volume variations and the shortened Li-ion diffusion induced from the porous structure with large specific surface area, as well as the protective effect from graphene nanosheets

Calculation of flow turbulence and analysis on screens setting-up in continuous and transonic wind tunnel

Turbulence intensity in test section is an important index to evaluate the flow-field performance of wind tunnel, and provide guarantee for model's dynamics and accurate test. The prediction model should be established to evaluate the effect of rectification design to ensure the turbulence-intensity index. Two methods are introduced and used to predict the turbulence-intensity of a continuous and transonic wind tunnel comparing with test results. It was found that the turbulence-intensity variation trend obtained from the two methods is basically same, turbulence-intensity attenuation is mainly concentrated in the first three screens, about 65%, the result calculated by model-one is 21% larger than the measured value and the model-two result is much closer. These two methods can be used to optimize the design of rectifying device effectively although the results obtained by two methods are slightly different form the measured value

Thermal properties of carbon black aqueous nanofluids for solar absorption

<p>Abstract</p> <p>In this article, carbon black nanofluids were prepared by dispersing the pretreated carbon black powder into distilled water. The size and morphology of the nanoparticles were explored. The photothermal properties, optical properties, rheological behaviors, and thermal conductivities of the nanofluids were also investigated. The results showed that the nanofluids of high-volume fraction had better photothermal properties. Both carbon black powder and nanofluids had good absorption in the whole wavelength ranging from 200 to 2,500 nm. The nanofluids exhibited a shear thinning behavior. The shear viscosity increased with the increasing volume fraction and decreased with the increasing temperature at the same shear rate. The thermal conductivity of carbon black nanofluids increased with the increase of volume fraction and temperature. Carbon black nanofluids had good absorption ability of solar energy and can effectively enhance the solar absorption efficiency.</p