间歇性大功率相变热沉研究

针对某300 W大功率间歇式热源,选用质量分数9.0％膨胀石墨-56号石蜡复合材料做相变工质,铝翅片做导热结构,基于FLUENT软件,采用等效比热容数学模型,在安全温度为65.0 ℃情况下,设计得到能稳定运行3 500 s的相变热沉.针对该相变热沉,为验证等效比热容数学模型的可靠性,搭建了相变热沉测试系统,研究了热源功...     

高温下吸热型碳氢燃料定压比热容在线测量

为提高吸热型碳氢燃料高温高压条件下比热容的测量精度,基于能量守恒的量热计理论,设计一套适用于高温高压的碳氢燃料定压比热在线测量系统。系统温度测量范围为450~900 K,测量压力可达10 MPa。选取环己烷和质量比1∶1正己烷-正庚烷二元混合物对测量系统进行标定,实验结果与文献的相对误差在±1%以内,相对误差绝对平均值小于0.32%。在此基础上对两种不同成分的吸热型碳氢燃料的定压比热进行了测量,温度为450~900 K,压力为2.0~5.0 MPa。实验结果表明:在低温区域范围内,碳氢燃料的比定压热容随温度的升高呈现近线性增长;在拟临界、临界温度时达到一个峰值,且峰值随压力的增加逐渐减小,且所对应温度点不断后移;大比热区后,燃料的比热容值随温度的升高急速增大。该测量系统的应用可为进一步提高碳氢燃料比热的测量温度范围创造条件。     

Improved electrochemical performance of modified natural graphite anode for lithium secondary batteries

Modified natural graphite is synthesized by surface coating and graphitizing process on the base of spherical natural graphite. The modified natural graphite is examined discharge capacity and coulombic efficiency for the initial charge–discharge cycle. Modification process results in marked improvement in electrochemical performance for a larger discharge capacity and better coulombic efficiency. The mechanism of the enhancement are investigated by means of X-ray powder diffraction, scan electron microscopy, and physical parameters examination. The proportion of rhombohedral crystal structure was reduced by the heat treatment process. The modified natural graphite exhibits 40 mAh g⁻¹ reduction in the first irreversible capacity while the reversible capacity increased by 16 mAh g⁻¹ in comparison with pristine graphite electrode. Also, it has an excellent capacity retention of ∼94% after 100 cycles and ∼87% after 300 cycles.     

Facile synthesis of nanometer-sized NiFe layered double hydroxide/nitrogen-doped graphite foam hybrids for enhanced electrocatalytic oxygen evolution reactions

We report a self-standing NiFe layered double hydroxide/nitrogen doped graphite foam (NiFe LDH/NGF) electrode for the oxygen evolution reaction (OER) prepared via a facile electrodeposition method. The electrode showed high electrocatalytic activity towards OER, exhibiting a low onset overpotential of 0.239 V and a small Tafel slope of 57.9 mV dec^?1 in basic electrolytes, as well as a good stability during the long-term cycling test. The outstanding electrocatalytic activity is mainly attributed to the synergy between the abundant catalytically active sites through good dispersion of NiFe LDH across NGF and fluent electron transport arising from NGF.     

Oxidation performance of graphite material in reactors

Graphite is used as a structural material and moderator for high temperature gas-cooled reactors (HTGR). When a reactor is in operation, graphite oxidation influences the safety and operation of the reactor because of the impurities in the coolant and/or the accident conditions, such as water ingress and air ingress. In this paper, the graphite oxidation process is introduced, factors influencing graphite oxidation are analyzed and discussed, and some new directions for further study are pointed out __________ Translated from Nuclear Power Engineering, 2007, 28(5): 50–53, 98 [译自: 核动力工程]     

Nitrogen-incorporated carbon nanotube derived from polystyrene and polypyrrole as hydrogen storage material

“Synthesis of nitrogen-doped carbon nanotubes from polymeric precursors (polystyrene and polypyrrole) by poly-condensation followed by carbonization under an inert atmosphere is reported. Three different carbonization temperatures (500 °C, 700 °C and 900 °C) were employed to synthesize three different carbon nanostructures with different morphologies. These were designated as NCNR-500 (nitrogen-doped carbon nanorods), NCBCT-700 (nitrogen-doped fused bead carbon nanotubes), and NCNT-900 (nitrogen-doped carbon nanotubes) according to morphology and carbonization temperature. Microstructure, morphology, porosity, and nitrogen content were characterized by several different techniques. The effects of carbonization temperature and the role of functional groups were also investigated. Total and excess hydrogen storage capacities of 2.0 wt% and 1.8 wt%, respectively, were measured at 298 K and 100 bar for the NCNT-900 material. This is higher than the capacities of the NCNR-500 and NCBCT-700 materials. NCNT-900 exhibited a porous structure with high specific surface area and total pore volume of 870 m/g and 0.62 cm³/g, respectively.     

Nitrogen doped lotus stem carbon as electrocatalyst comparable to Pt/C for oxygen reduction reaction in alkaline media

The nitrogen doped carbon with high content of pyridine N and porous structure indicates high activity for oxygen reduction reaction (ORR). In this paper, nitrogen doped lotus stem carbon (N-LSC) with 6.3 at% of N (containing 52 at% of pyridine N) and porous structure is developed by using lotus stem as carbon source and dopamine hydrochloride as nitrogen source. The ORR activity, stability and methanol tolerance are characterized. The results show that the N-LSC has comparable activity to Pt/C, and much better methanol tolerance and stability than Pt/C. The porous structure and high content of pyridine N are believed to lead to the high ORR performances of the N-LSC.     

碳化硅杂质对石墨加热棒温度场的影响数值模拟研究

运用ANSYS软件,以工业常用的石墨电加热棒为研究对象,对含有大颗粒碳化硅杂质的石墨电加热材料进行三维稳态传热数值模拟计算,分析了不同加热电流下碳化硅杂质颗粒大小对石墨加热棒温度场的影响关系.     

Bridging-nitrogen defects modified graphitic carbon nitride nanosheet for boosted photocatalytic hydrogen production

Reinforcing the visible photon absorption and charge separation are the key issues to maximize the photocatalytic performance of graphitic carbon nitride. Herein, holey bridging-nitrogen-defected graphitic carbon nitride nanosheets were prepared through solid-state copolymerization and subsequently thermal annealing with melamine and hexamethylenetetramine as the precursors. Numerous pores and bridging nitrogen defects that embedded into the thin-layer framework were evidenced through comprehensive characterization. The synthesized textural and electronic structure enables the significant improvement of photocatalytic hydrogen production, with the optimized sample of D-CNNS(0.3) representing a hydrogen evolution rate of 2497.1 μmol?g^?1?h^?1 under visible light irradiation (λ > 420 nm). This is about 10.4 and 41.1 folds improvement compared with pristine nanosheets and bulk carbon nitride, respectively. Both experimental and theoretical results demonstrate the bridging nitrogen defects are beneficial to enhance photoabsorption, promote charge separation and transfer. Together with the enlarged surface area, the optimized nanosheet sample shows a dramatically improved quantum yield in visible region.