Numerical investigation of hydrodynamic and heat transfer performances of nanofluids in a fractal microchannel heat sink

Heat transfer and hydrodynamic performances for nanofluids, Al₂O₃‐water and SiO₂‐water, are numerically investigated with different nanoparticles’ volume fractions and the initial velocities in a fractal microchannel heat sink. The fractal microchannel is 100 μm × 100 μm in the inlet cross‐section, and the length at the 0th level is 2000 μm. A constant heat flux of 500 kW/m² was applied to the bottom wall of the fractal microchannel heat sink. The heat transfer and hydrodynamic performances of different cases are discussed in terms of the mean heat transfer coefficient, mean base temperature, pressure loss, thermal resistance, friction factor f/f₀, and COP/COP₀. Results indicate that increasing the initial velocity and nanoparticles’ volume fraction lead to an enhanced heat transfer at the expense of pressure loss. Al₂O₃‐water has a higher mean heat transfer coefficient and pressure drop than that of SiO₂‐water, a lower f/f₀, mean base temperature, thermal resistance, and COP/COP₀. Ultimately, as compared to pure water, the heat transfer coefficients of 4% Al₂O₃‐water increased by 7.53%, 7.80%, 8.00%, 8.14%, 8.16%, and 8.30%, and the pressure drops increased by 32.09%, 31.41%, 30.81%, 30.05%, 29.21%, and 28.58%, respectively, corresponding to the initial velocities by 4, 5, 6, 7, 8 and 9 m/s.     

Effect of carriers on deposition morphologies and catalytic performances of NiCo2O4

In this study, NiCo₂O₄ with different morphologies were fabricated using carriers by homogeneous coprecipitation combined with a sintering method. The phase and microstructure were characterized by XRD, SEM, EDS, TEM and BET, and the catalytic performances were investigated by NaBH₄ hydrolysis experiments. These studies revealed that the deposition morphology of NiCo₂O₄ can be adjusted by using different kinds of carrier templates, and the supported NiCo₂O₄ samples presented the pine-needle-like, network-like, ball-cactus-like and dandelion-like morphologies respectively. The optimal catalytic activity, durability and stability make the network-like NiCo₂O₄ an appropriate catalyst for hydrogen generation of NaBH₄ hydrolysis. It was found that the network-like NiCo₂O₄ is the most reusable and durable catalyst for ten consecutive cycles and 100% hydrogen generation conversion rate without obvious decrease among these morphologies.     

Vacancy-engineered V2O5-x films for ultrastable electrochromic applications

In the present study, we prepared vacancy-engineered V₂O_5-x films for electrochromic (EC) applications. To investigate the vacancy effect of V₂O_5-x films with high EC performance capabilities, precursor concentrations of V-based sol solutions were varied at 1 wt%, 5 wt%, and 10 wt%. Among them, V₂O_5-x films with a precursor concentration of 5 wt% (V₂O₅-5wt%) showed superior EC performance outcomes due to the (001)-plane-oriented crystal structure, which provides high electrical conductivity with the oxygen vacancy (V_o). In addition, the gravel-like uniform surface morphology with the optimized film thickness provides a stable electrochemical reaction during the EC measurement. As a result, V₂O₅-5wt% exhibited fast switching speeds (2.1 s for coloration and 3.6 s for bleaching), high transmittance modulation (ΔT) (51.32%), high coloration efficiency (CE) (52.3 cm²/C), and excellent cycle stability (85.85% ΔT retention after 500 cycles). In addition, V₂O₅-5wt% showed energy storage capability of 443.7 F/g at a current density of 2 A/g, thus proving its potential for use in multi-functional applications. Therefore, these results provide valuable insight related to the engineering of vacancies in EC films to achieve high-performance EC devices and additional multi-functional applications.     

Efficient recursive least squares parameter estimation algorithm for accurate nanoCMOS variable gain amplifier performances

ABSTRACT

With the aggressive scaling of integrated circuit technology, parametric estimation is a critical task for designers who looked for solutions to the challenges of some Nanoscale CMOS parameters. This paper presented the prediction of primary parameters of CMOS transistor for 16 nm to 10 nm process nodes using both of Bisquare Weights (BW) method and a novel recursive least squares (RLS) parameter estimation algorithm. The proposed RLS algorithm consists of the minimisation of a quadratic criterion relating to the prediction error in order to attain the best estimated parameters of the developed mathematical model. The obtained results thanks to the proposed RLS algorithm were better than those reached using the BW method. Comparisons between Predictive Technology Model (PTM) data and parameters estimated with RLS algorithm were made to check the validity and the consistency of the proposed algorithm. These predicted primary parameters were helpful to estimate and to optimise the performances of the Variable Gain Amplifier (VGA) which was a basic circuit element with a key role in the design of new upcoming receivers.     

Hierarchically porous carbon derived from the activation of waste chestnut shells by potassium bicarbonate (KHCO3) for high-performance supercapacitor electrode

3D hierarchical porous carbon consisting of micropores, mesopores and macropores was successfully prepared through the activation of chestnut shell via KHCO₃. The influence of KHCO₃/chestnut shell ratio on the textural properties was carefully investigated and the structure, micrographs, and surface chemical status of the materials were expressed via X-Ray diffraction (XRD), transmission electron micrographs (TEM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), respectively. With the optimized amount of KHCO₃, high specific pore surface area (2298 m² g^-1) and high total pore volume (1.51 cm³ g^-1) were achieved, endowing an advantageous electrochemical characteristics for the electrode as ultracapacitors in three-electrode system. At 2 A g^-1, a high specific electric capacity of 387 F g^-1 was reached. The remarkable electrochemical performances are mainly due to hierarchical porous structure with the high specific surface area (SSA) and the eminent total pore volume. It means that this hierarchical porous carbon prepared by activated by using KHCO₃ would have more promising foreground in the field of energy storage.     

EMD铁劣化原因分析及电化学活性

用数据统计方法对大量现场数据进行分析,确认EMD后处理中,由半成品到成品铁劣化现象,并确定铁劣化区间在0.0296％至0.0401％,以及铁劣化对EMD电化学活性的影响。     

Vanadium Doping Enhanced Electrochemical Performance of Molybdenum Oxide in Lithium‐Ion Batteries

Molybdenum trioxide (MoO₃) suffers from poor conductivity, a low rate capability, and unsatisfactory cycling stability in lithium‐ion batteries. The aliovalent ion doping may present an effective way to improve the electrochemical performances of MoO₃. Here, it is shown, by first‐principle calculations, that doping MoO₃ with V by 12.5% can modulate significantly electronic structure and provide a small diffusion barrier for enhancing the electrochemical performance of MoO₃. The ultralong Mo_0.88V_0.12O_2.94 nanostructures, which retain the h‐MoO₃ structure and present an exceptionally high conductivity and fast ionic diffusion due to the substitution of V, facilitating lithiation/delithiation behavior, and induce a fine nanosized structure with a reduced volume change are prepared. As a result, the stress and strain are alleviated during the Li‐ion intercalation/deintercalation processes, improving the cycling stability and rate capability. Such a large improvement in the electrochemical properties can be ascribed to the stabilizing effect of V, the small migration energy barrier, and short diffusion path, which arise from the introduction of V into MoO₃. The unique engineering strategy and facile synthesis route open up a new avenue in modifying and developing other species of electrode materials.     

Electrochemically treated graphite/poly(3,4-ethylenedioxythiophene)-carbon nanotubes electrode: facile preparation and remarkable enhancement in electrochemical performances

Abstract

This work reports an approach to significantly improve the supercapacitive properties of poly(3,4-ethylenedioxythiophene)-carbon nanotubes (PEDOT-CNTs) hybrid electrodes. Specifically, a facile electrochemical treatment method is put forward to roughen graphite (G). After that, the electrochemically treated graphite (EG) acts as the substrate to load the PEDOT-CNTs composites by electrochemical co-deposition. The obtained EG/PEDOT-CNTs electrode shows substantially enhanced electrochemical performances with respect to G/PEDOT-CNTs electrode, caused by optimal electron transfer pathways between PEDOT-CNTs composite films and the roughened EG substrate. Here, the EG/PEDOT-CNTs electrode achieves a high specific capacitance of 278.7?F g^?1 at 1?A g^?1, higher than those of PEDOT based composite electrodes in various studies reported recently. This study demonstrates that the roughening treatment of the electrode substrate is an effective approach to substantially promote the supercapacitive properties of electrodes.     

脲醛树脂化学构造与胶接性能、甲醛释放量及固化特性关系的研究

采用3种典型的脲醛(UF)树脂合成方法合成UF树脂,并对合成UF树脂的性能、化学构造、胶接性能、甲醛释放量及其固化历程进行了研究。揭示了UF树脂化学构造与合成方法、胶接性能、固化特性及甲醛释放量之间的相关关系,证明UF树脂的胶接性能、固化历程、甲醛释放量与UF树脂的化学构造直接相关,尤其是树脂中羟甲基含量与结合方式、亚甲基的构造对树脂性能影响最大。     

Preparation of porous spherical α-Ni(OH)2 and enhancement of high-temperature electrochemical performances through yttrium addition

Through homogeneous precipitation method, uniform spherical α-Ni(OH)₂ particles were obtained at appreciate aging time in urea solution without any help of templates or dispersants. From SEM images, aging time exhibited great effects on the morphology of as-synthesized α-Ni(OH)₂. Also, long aging time helped to improve the electrochemical performances of α-Ni(OH)₂. It was found that the proper aging time was 12 h. However, α-Ni(OH)₂ showed low charge/discharge capacities at high temperatures. Therefore, yttrium was added to improve the high-temperature electrochemical performances of α-Ni(OH)₂. The influences of doping ratios of Y on the morphologic and high-temperature electrochemical characteristics were investigated through XRD, SEM, TEM, constant current charge/discharge, and cyclic voltammetric measurements. The α-Ni(OH)₂ samples with the addition of about 5.8 mol% Y showed a discharge capacity of 250 mAh/g at 0.2 C rate and 60 °C, much higher than that of α-Ni(OH)₂ without Y dopants (157 mAh/g).