[en] The continuous phase transformation from the layered structure to the spinel-like phase seriously degrades the electrochemical properties of Li-rich layered oxides in Lithium-ion batteries. Herein, heterostructured Li-rich cathode materials Li[Li_0.2Ni_0.17Co_0.07Mn_0.56]O₂ in conjunction with different contents of Zr-containing phosphate (ZCP) coating layers were prepared. The structural and electrochemical characterizations reveal that the ZCP surface layer, which not only prevents electrolyte from eroding the Li-rich core and thus suppressing the fast growth of solid electrolyte interface film and charge transfer resistance on the surface of oxide particles, but also enhances the structural and thermal stabilities of the electrode. As a result, the 3 wt.% coated sample delivers an initial discharge capacity of 216 mAh g⁻¹ with a coulombic efficiency of 80%, compared to 202 mAh g⁻¹ and 71%, respectively, for the bare sample. Particularly, the coated sample demonstrates excellent cycling stability with a capacity retention of 91% within 100 cycles, and higher thermal stability.

[en] In this work, well dispersed ethylene glycol (EG) based nanofluids containing ZnO nanoparticles with different mass fractions between 1.75% and 10.5% were prepared by a typical two-step method. Structural properties of the dry ZnO nanoparticles were measured with X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). Thermal transport properties including thermal conductivity and viscosity were experimentally measured for the nanofluids. The experimental results show that thermal conductivity increases slightly with increasing the temperature from 15 to 55 °C. It depends strongly on particle concentration and increases nonlinearly with the concentration within the range studied. The enhanced value is higher than the value predicted by the Hamilton and Crosser (H–C) model. Moreover, viscosity increases with concentration as usual for ZnO nanoparticles and decreases with temperature. For an analysis of the rheological behaviors, it shows that ZnO-EG nanofluids with mass fraction wt.% ≤ 10.5 demonstrate Newtonian behaviors

[en] Highlights: • Controllable heat transfer was verified by both experiments and simulations. • The analysis of heat transfer on magneto-hydrodynamics are presented. • A magnetically enhanced heat transfer method was exhibited. • Average heat transfer efficiency is improved by 12.2% under a magnetic field. • Local heat transfer efficiency can be improved by 30.2% under a magnetic field. -- Abstract: Currently, nanofluids have been used in the energy conversion process because of their superior optical property and high thermal conductivity. Nanofluids with controllable heat transfer are superior for the tuning the heat transfer speed and efficiency. Herein, we report a method for magnetically increasing heat transfer for use with magnetic nanofluids in a straight tube. Convective heat transfer simulations were performed and the results were found to be consistent with experimental results. The heat exchange performance of magnetic nanofluids were compared with based fluid, and the analysis of heat transfer on magneto-hydrodynamics is presented. Moreover, the effects of Reynolds number, magnetic field horizontal distances, rotation angles and strengths are investigated on the convective heat transfer performance under various magnetic fields. Compared to conventional forced convective heat transfer, the magnetically enhanced heat transfer strategy extends the heat transfer thresholds efficiency and provides more accurate heat transfer enhancement. The effect of magnetic field on heat transfer characteristics occurs in a local area rather throughout tube. The average heat transfer efficiency is increased by 12.2% while the local heat transfer efficiency can be improved more than 30.2% under an applied magnetic field. These results illustrate an advanced method for controlling convective heat transfer by regulating a magnetic field.

[en] Highlights: • Optical properties of core-shell NPs were discussed systematically. • Absorption efficiency can be adjusted by the core-shell or mixing ratios of NPs. • Optimized parameters of the core-shell NPs for solar absorption were obtained. • Efficiency of Au-decorated SiO₂ NPs was superior to Au NPs and SiO₂ NPs. - Abstract: In this study, the properties of various types of core-shell nanoparticles (NPs) were evaluated using the finite difference time domain (FDTD) method towards the enhancement of solar absorption performance. Results showed that the resonance wavelength of SiO₂@Au NPs lay in the 540–900 nm range, covering the near-infrared and visible regions. The resonance wavelength of SiO₂@Ag NPs lay in the 390–830 nm range, covering the entire visible region. SiO₂@Au nanofluid with a core-shell ratio of φ = 0.2 exhibited the highest solar absorption efficiency with 64% less Au consumption compared to pure Au NPs. For mixed nanofluids, the mixtures featuring core-shell ratios of 0.1 and 0.6 with mixing ratios of 0.5 for SiO₂@Au and 0.6 for SiO₂@Ag gave the highest absorption efficiencies. In addition, the peak solar absorption efficiency of a mixed nanofluid of SiO₂@Au (φ = 0.1) and SiO₂@Ag (φ = 0.4) with a mixing ratio of 0.58 was as high as 94.4%. Solar thermal conversion experiments revealed that, under the same conditions, a Au-decorated SiO₂ nanofluid showed a comparable efficiency to the calculated solar absorption efficiency of the SiO₂@Au core-shell nanofluid (∼95.2%); it was as high as 95.9%, higher than those of Au NPs and SiO₂ NPs. These results showed that adjusting the core-shell ratios and tuning the mixing ratios of different nanofluids are two efficient methods to enhance the solar absorption efficiencies of SiO₂@Au and SiO₂@Ag NPs under the optimal conditions.

[en] Highlights: • Magnetic recoverable Fe₃O₄@TiO₂ nanoparticles were successfully prepared. • A multifunctional system was set up for water purification. • Controllable recovery rate and efficiency can be adjusted by magnetic field. - Abstract: In recent years, nanoscale particles have been applied in the utilisation of solar energy due to their excellent properties. In light of the multiple functions of composite nanoparticles, some solar-assisted systems have been developed and exhibited comprehensive photoelectric and photo-thermal transformation effects. However, the presence of nanoparticles in these systems can cause secondary pollution and severely limit large-scale application of the solar technology. Herein we developed a recyclable photo-thermal conversion and purification system based on Fe₃O₄ nanoparticles decorated with TiO₂ nanoparticles, which could be separated from water under the action of a magnetic force. Under the solar illumination power of 1 sun (1 sun = 1000 W·m⁻²), thermal receiver efficiency of 76.4% and Rhodamine B degradation efficiency of 85% were obtained with a 0.1 g/L Fe₃O₄@TiO₂ nanofluid. With the increase of the solar illumination power, the degradation efficiency has been increased to 94%. The recovery rate and efficiency could be controlled by adjusting the magnetic field strength and the magnetic property of Fe₃O₄@TiO₂ nanoparticles. This study provides an approach to not only significantly reduce material consumption in the design of solar devices, but also to realise broad solar energy applications for water purification and photo-thermal conversion.

[en] Highlights: • The heat transfer could be controlled by the strength and direction of magnetic field. • Thermophysical properties of Fe₃O₄@CNT nanofluid were measured and used in simulation. • The influence of magnetic fields was researched numerically and experimentally. - Abstract: Currently, natural convection with nanofluid depends on the addition of nanoparticles with a high thermal conductivity to increase the heat transfer performance, often leading to limited increase in heat transfer rate and efficiency. Herein, a magnetically controlled heat transfer method was evaluated. This method enables a rectangular enclosure filled with Fe₃O₄@CNT nanofluid to achieve controllable heat exchange. Compared with conventional natural convective heat transfer, the magnetically controlled heat transfer method increased the thresholds of heat transfer efficiency by increasing the convective heat transfer. The heat transfer and flow of natural convection can be controlled by the strength and direction of magnetic field. The increase in heat transfer depends on the direction of magnetic field, and the strength of magnetic field determines the degree of heat transfer. This study provides a method to achieve superior convective heat transfer coefficients by controlling the magnetic nanoparticle distribution in a rectangular enclosure.

[en] Highlights: • A freeze-drying method was proposed to formulate solar salt-based SiO₂ nanofluids. • A modified lattice Boltzmann model was used to simulate the forced convective heat transfer. • 1.0 wt% was the optimal SiO₂ nanoparticle mass fraction for heat transfer application. • Parameter analysis was conducted to investigate the factors influencing heat transfer characteristics. • Shah-London correlation was examined and found can be used for solar energy application. -- Abstract: Nowadays, molten salts are widely used in concentrated solar plants as working media to transfer and store solar energy. However, the relatively poor thermal properties of molten salts have restricted their further application. Nevertheless, the addition of nanoparticles to molten salts excellently improves these thermal properties. In present work, solar salt-based nanofluids were prepared using a lyophilizer. The specific heat of solar salt-based SiO₂ nanofluids was experimentally measured based on the sapphire method, and its heat transfer performance was numerically investigated using the lattice Boltzmann method. Results indicated that an optimum nanoparticle mass fraction that could enhance heat transfer performance existed. This optimum nanoparticle mass fraction, which was found to be 1.0 wt%, improved the heat transfer coefficient and Nu number by 8.58 and 7.29%, respectively. The parameter analysis indicated that the considerably large change in the specific heat dominated the change in heat transfer performance. Meanwhile, the simulation results of the average Nu numbers exhibited good agreement with the Shah-London correlation prediction to within ±3.0%, indicating the feasibility of using this correlation in designing heat exchangers that utilize solar salt-based SiO₂ nanofluids.

[en] Highlights: • C-Au-TiO₂ solar absorber was prepared in this study. • A good photo-thermal conversion property was verified by experiments. • A novel system with the solar absorber for evaporation enhancement was designed. • The enhancement was investigated by experiments and theoretical calculations. Solar steam generation, a typical solar energy utilization way, has wide applications and attracts many researches, such as the enhancement achieving by numerous nanomaterials and porous membranes. However, some issues need to be solved (e.g., blockage of pore structures and poisoning of film nanoparticles (NPs)), which are critical for developing sustained and efficient evaporation processes. In this sense, we developed herein a novel evaporation method involving a thin water layer and a highly efficient solar absorber for enhanced steam generation. This technology prevented pore blockage and poisoning of NPs by employing a dense surface structure and continuous water flow. A C-Au-TiO₂ solar absorber prepared by a sol-gel method with a superior photo-thermal conversion capacity, even for lights with large angles of incidence was the key to enhance the solar steam generation process. By experiments and theoretical calculations for solar evaporation, the steam generation performance and heat change process were investigated. It was found that improving the light absorption of the solar absorber and reducing the thermal loss were effective methods to enhance evaporation rate and efficiency, while reducing the water height could cut down the time needed to reach stable stage. And the C-Au-TiO₂ solar absorber achieved a significantly enhanced solar steam generation, which may pave the way for developing new highly efficient solar steam generation paths.

[en] Water scarcity is a global challenge and is expected to affect two-thirds of the world population in the coming decades. The augmentation of freshwater resources is the need of the hour, in perspective of rapid globalization and the rise in world population with every passing day. The current investigation evaluates the performance of an integrated model of conventional solar still (CSS), flat plate collector (FPC) and parabolic trough collector (PTC) for the production of potable water using ZnO, Al₂O₃, TiO₂ and CNT nanomaterials. Nanofluid samples were prepared using a standard two step-method and characterized using UV-Vis (Ultraviolet-Visible) spectroscopy and scanning electron microscopy (SEM). The experimental performance of different combinations of CSS, FPC and PTC in terms of water yield and photothermal efficiency was evaluated with and without nanomaterials. The experimental results revealed that the highest water production rate of 0.478 lm^-2 h^-1 (LMH) was in case of integrated system consisting of CSS, FPC and PTC using CNT based nanofluid, which was 153% higher than that of CSS without nanoparticles. The water yield of the integrated system was 0.458, 0.466 and 0.466 LMH for ZnO, TiO₂ and Al₂O₃ nanofluids, respectively at 0.1 wt% concentration. The overall photothermal performance of the integrated system was improved by 24% with 0.1 wt% particle concentration over the base fluid irrespective of the type of nanomaterial. (author)

[en] Highlights: • Stable binary nitrate eutectic salt based Al_2O_3 nanofluids were prepared. • A maximum enhancement of 8.3% on c_p was obtained at 2.0 wt.% nanoparticles. • MD simulation results show good agreement with experimental data. • The change in Coulombic energy contributed to most of the large change in c_p. - Abstract: Molten salts can be used as heat transfer fluids or thermal storage materials in a concentrated solar power plant. Improving the thermal properties can influence the utilization efficiency of solar energy. In this study, the effect of doping eutectic binary salt solvent with Al_2O_3 nanoparticles on its specific heat capacity (c_p) was investigated. The effects of the mass fraction of nanoparticles on the c_p of the composite nanofluid were analyzed, using both differential scanning calorimetry measurements and molecular dynamics simulations. The specific heat capacity of the nanocomposites was enhanced by increasing the nanoparticle concentration. The maximum enhancement was found to be 8.3%, at a nanoparticle concentration of 2.0%. A scanning electron microscope was used to analyze the material morphology. It was observed that special nanostructures were formed and the specific heat capacity of the nanocomposites was enhanced by increasing the quantity of nanostructures. Simulation results of c_p agreed well with the experimental data, and the potential energy and interaction energy in the system were analyzed. The change in Coulombic energy contributed to most of the large change in c_p, which explains the discrepancy in values between conventional nanofluids and molten salt-based nanofluids.