Numerical modeling of hydrogen catalytic reactions over a circular bluff body

This paper was intended to delineate numerical research for hydrogen catalytic combustion over a circular cylinder. The wire/rod-type catalytic reactor is a simple geometry reactor with an economical design with less pressure loss. For the single rod in the reaction channel, the flow characteristic and the difference of conversion efficiency between non-gas-phase reaction and gas-phase reaction have been delineated in the present study. The flow field and the chemical reactions were numerically modeled using 2D Large Eddy Simulation combined with the gas-phase and surface reaction mechanisms. The results show that the current numerical simulation has been validated to precisely predict the vortex shedding and its frequency in the cold flows. Despite the variation trends being dominated by the upstream flow, the vortex shedding phenomena were affected by the flue gas generated from the rod surface. It can be seen from the linear relationship between the vortex shedding frequency of reacting flow and Reynolds Number. It is noted that the vortex shedding vanished if the gas-phase reaction was ignited in the reaction channel. In addition, the geometric modified conversion efficiency was proposed to delineate an indicator that could be potential for the optimization of rod-type catalytic reactor. In summary, the fundamental study of a rod in a 2D flow channel can provide information for optimizing the catalytic design or the rod array arrangement in the reactor. Moreover, the rod can also be a partial catalytic flame holder to ignite and stabilize the gas-phase reaction. The obtained results could be the potential for practical applications of rod-type catalytic combustion, catalytic gas turbine, hydrogen generation, partially catalytic reaction flame holder, and other catalytic reactions that can be appreciated.     

C105管桩混凝土设计参数取值的探讨

通过试验得出了C105混凝土100 mm×100 mm×100 mm立方体非标准试件抗压强度换算系数以及C105混凝土的标准方差和强度变异系数。采用理论计算,得到了棱柱体抗压强度与立方体抗压强度的比值α_c1,并与试验实测平均值进行了比较,验证了理论计算方法的可行性。此外,通过对比分析,探讨了直接外延法和引用公式法两种C105混凝土设计参数计算方法的正确性,研究结果可为C105管桩混凝土的设计和应用提供参考。     

Compressive strength and microstructure of alkali-activated fly ash/slag binders at high temperature

This paper reports the results of the compressive strength and microstructure of various alkali-activated binders at elevated temperatures of 300 and 600 °C. The binders were prepared by alkali-activated low calcium fly ash/ground granulated blast-furnace slag at ratios of 100/0, 50/50, 10/90 and 0/100 wt.%. Specimens free of loading were heated to a pre-fixed temperature by keeping the furnace temperature constant until the specimens reached a steady state. Then the specimen was loaded to failure while hot. XRD, SEM and FTIR techniques were used to investigate the microstructural changes after the thermal exposure. The fly ash-based specimen shows an increase in strength at 600 °C. On the other hand, the slag-based specimen gives the worst high-temperature performance particularly at a temperature of 300 °C as compared to ordinary Portland cement binder. This contrasting behaviour of binders is due to their different binder formulation which gives rise to various phase transformations at elevated temperatures. The effects of these transformations on the compressive strength are discussed on the basis of experimental results.     

Conversion of natural gas jet flame burners to hydrogen

In a study of conversion from CH₄ to H₂, jet flame characteristics of these gases and their blends are compared on a burner diameter scale of mm. Low velocity H₂ and CH₄ jets, burned on pipes of different diameters, indicate higher blow-off limits for H₂, but lower heat release rates, a consequence of its lower specific energy. Compensation for this might be obtained through increased H₂ flow velocity, or a small increase in pipe diameter. Blended CH₄/H₂ flames have lower heat release rates than CH₄ alone, yet small proportions of H_2, with CH₄ might still be burned, on a CH₄ burner. Throughout, fundamental understanding is enhanced through two dimensionless groups: laminar flame thickness normalised by burner diameter, δ_k/D, and the dimensionless flow number, U1. These suggest an optimal role for H₂ combustion, utilizing its high acoustic and blow-off velocities, in high intensity, subsonic, combustors, at low δ_k/D, and high U1.     

EPS2000和AutoCAD平台下图形文件的无缝转换

探讨了通过EPS2000的模块设置将图形件转换成AutoCAD平台下的图形件的方法，并应用适当的方法和程序处理来实现测图系统问图形件的无缝转换，达到资源合理共享的目的。     

钢－混凝土组合梁计算程序

针对当前钢－混凝土组合梁设计主要采用人工计算的弊端，提出ＣＰＳ计算程序，在计算荷载效应时采用了有限元、离散元等力学方法和优化设计手段。实际应用证明：程序设计合理，是解决复杂多变的设计计算问题的有效方法。     

回弹法检测长龄期混凝土抗压强度的探讨与工程实践

参照行业标准(JGJ/T 23-2001)和地方标准(DB21/T834-2000),计算了实际工程长龄期混凝土的换算强度,并与芯样换算抗压强度进行了比较;提出了拓展回弹法检测长龄期混凝土抗压强度技术应用范围的建议.     

Recovery of nano-calcium fluoride and ammonium bisulphate from phosphogypsum waste

ABSTRACT

The production of phosphoric acid generates an enormous amount of phosphogypsum with emission of toxic fluorine acid gas. To remedy these environmental problems, a novel and a simple procedure permits converting phosphogypsum waste by recycled fluorine acid into valuable products. The obtained results confirm the efficiency of this procedure, which synthesises at room temperature the calcium fluoride in the form of nano-crystalline powder and the ammonium bisulphate salt from the exact stoichiometric proportions of phosphogypsum, hydrofluoric acid and ammonia. The total conversion of phosphogypsum is achieved after reaction time equal to one hour and a half. Generally, this novel procedure offers not only a solution for reducing phosphogypsum waste and fluorine gas emission, but also gives rise to valuable products, useful to industry and agriculture.     

Modification of X-ray Generator by Energy Reusing

X-ray is an important tool for charactering and analyzing materials. However, current X-ray generation is cost with low efficiency. For X-ray tube, which is mostly used in laboratories, only has an energy usage of 1% with all other energy dissipated into tremendous heats, and it needs continuous cool water flows to cool down the cathode. It generates X-ray by the bremsstrahlung of high energy electrons bombarding on the cathode target, the bremsstrahlung would contain X-ray with sufficiently high energy of the electrons. But most part of the electron energy becomes heats. In order to generate X-ray more cheaply with higher efficiency, methods about reusing the released heats during the working of the X-ray tube are brought up. Mimicking the photovoltaic effect, nonequilibrium carriers could also be injected via thermion emission when heating a metal, such injection is same to that of photonic injection which produces electromotive in a photovoltaic cell. In a photovoltaic cell the electron-hole pair generated by incident photons are nonequilibrium carriers that causes electromotive, while the thermion emission creates such electron-hole pairs via thermal excitation. Connecting metals suitable for thermion emission from the cathode into the p-n junction so that thermions as nonequilibrium carriers can be well injected into the p-n junction when the metals are heated by the cathode, with Thomson effect which enhances such injection, a thermal voltaic cell can be constructed and it can produce electricity only by heating the metals outside. Applying such thermal voltaic cell into current X-ray tube, it would produce electricity while absorbing the tremendous heats emerges when X-ray tube is working. Water flows are still used to control the temperature, but letting them boiling to keep the cathode at a temperature best for thermal voltaic cell, and the vapor may be used to drive a mini thermal power plant. In this way, the energy usage could be modified to a higher proportion. Stepwise up-conversion is possible to generate X-ray more cheaply but there are no suitable materials so far.     

Optimization of the dye-sensitized solar cell performance by mechanical compression

In this study, the P25 titanium dioxide (TiO₂) nanoparticle (NP) thin film was coated on the fluorine-doped tin oxide (FTO) glass substrate by a doctor blade method. The film then compressed mechanically to be the photoanode of dye-sensitized solar cells (DSSCs). Various compression pressures on TiO₂ NP film were tested to optimize the performance of DSSCs. The mechanical compression reduces TiO₂ inter-particle distance improving the electron transport efficiency. The UV–vis spectrophotometer and electrochemical impedance spectroscopy (EIS) were employed to quantify the light-harvesting efficiency and the charge transport impedance at various interfaces in DSSC, respectively. The incident photon-to-current conversion efficiency was also monitored. The results show that when the DSSC fabricated by the TiO₂ NP thin film compressed at pressure of 279 kg/cm², the minimum resistance of 9.38 Ω at dye/TiO₂ NP/electrolyte interfaces, the maximum short-circuit photocurrent density of 15.11 mA/cm², and the photoelectric conversion efficiency of 5.94% were observed. Compared to the DSSC fabricated by the non-compression of TiO₂ NP thin film, the overall conversion efficiency is improved over 19.5%. The study proves that under suitable compression pressure the performance of DSSC can be optimized.