Kinetic Monte Carlo simulation of hydrogen production from photocatalytic water splitting in the presence of methanol by 1 wt% Au/TiO2

In this research, using the kinetic Monte Carlo simulation (KMC), the hydrogen production from a water-methanol mixture using Au/TiO₂ photocatalyst is investigated. A mechanism is proposed, and the rate constants of the reaction steps are specified. The reaction rate constants of different steps and the concentration of the active sites on the photocatalyst surface were determined. An excellent match between simulated and experimental data confirms the results. The electron-hole pair production, methanol adsorption on the photocatalyst surface, and electron-hole recombination steps are considered the most critical steps. To study the effects of independent variables (initial concentration of methanol, photocatalyst dosage, pH, and time of reaction) on the produced hydrogen, a combination of KMC simulation and design of experiment was employed. The concentration of photocatalysis has the highest and pH has the lowest effect on the hydrogen production. The optimal conditions for photocatalytic hydrogen production are presented.     

Centimeter-scale low-damage micromachining on single-crystal 4H–SiC substrates using a femtosecond laser with square-shaped Flat-Top focus spots

Femtosecond (fs) lasers have been proved to be reliable tools for high-precision and high-quality micromachining of ceramic materials. Nevertheless, fs laser processing using a single-mode beam with a Gaussian intensity distribution is difficult to obtain large-area flat and uniform processed surfaces. In this study, we utilize a customized diffractive optical element (DOE) to redistribute the laser pulse energy from Gaussian to square-shaped Flat-Top profile to realize centimeter-scale low-damage micromachining on single-crystal 4H–SiC substrates. We systematically investigated the effects of processing parameters on the changes in surface morphology and composition, and an optimal processing strategy was provided. Mechanisms of the formation of surface nanoparticles and the removal of surface micro-burrs were discussed. We also examined the distribution of subsurface defects caused by fs laser processing by removing a thin surface layer with a certain depth through chemical mechanical polishing (CMP). Our results show that laser-induced periodic surface structures (LIPSSs) covered by fine SiO₂ nanoparticles form on the fs laser-processed areas. Under optimal parameters, the redeposition of SiO₂ nanoparticles can be minimized, and the surface roughness Sa of processed areas reaches 120 ± 8 nm after the removal of a 10 μm thick surface layer. After the laser processing, micro-burrs on original surfaces are effectively removed, and thus the average profile roughness Rz of 2 mm long surface profiles decreases from 920 ± 120 nm to 286 ± 90 nm. No visible micro-pits can be found after removing ~1 μm thick surface layer from the laser-processed substrates.     

A new synthetic metamodel methodology for liquid‐propellant engine's cooling system optimization

The present paper strives for optimization of the cooling system of a liquid‐propellant engine (LPE). To this end, the new synthetic metamodel methodology utilizing the design of experiment method and the response surface method was developed and implemented as two effective means of designing, analyzing, and optimizing. The input variables, constraints, objective functions, and their surfaces were identified. Hence, the design and development strategy of combustion chamber and nozzle was clarified, and 64 different experiments were carried out on the RD‐161 propulsion system, of which 47 experiments were approved and compatible with the problem constraints. This engine used all three modes of cooling: the radiation cooling, the regenerative cooling, and the film cooling. The response surface curves were drawn and the related objective function equations were obtained. The analysis of variance results indicate that the developed synthetic model is capable to predict the responses adequately within the limits of input parameters. The three‐dimensional response surface curves and contour plots have been developed to find out the combined effects of input parameters on responses. In addition, the precision of the models was assessed and the output was interpreted and analyzed, which showed high accuracy. Therefore, the desirability function analysis has been applied to LPE's cooling system for multiobjective optimization to maximize the total heat transfer and minimize the cooling system pressure loss simultaneously. Finally, confirmatory tests have been conducted with the optimum parametric conditions to validate the optimization techniques. In conclusion, this methodology optimizes the LPE's cooling system, a 2% increase in the total heat transfer, and a 38% decrease in the pressure loss of the cooling system. These values are considerably large for the LPE design.     

Sand-ejecting fire extinguisher parameter sensitivity analysis based on DOE and CFD-DEM coupling simulations

To get more accurate quantitative impact effects of selective parameters of the sand-ejecting fire extinguisher on the scattering results by the CFD-DEM coupling method, orthogonal experimental design, analysis of range and variance, full factorial design and the OFAT design were used in this paper. The single impact effects and mixed impact effects of blade number, blade incidence and sand mass flow on scattering vertical distance and inclination were analysed and concluded, as well as the details of the sand distribution. The results show that only the sand mass flow has the dominating influence on the vertical distance, while all three factors have no significant influence on the scattering inclination. The larger the sand mass flow is, the more obvious influence of air resistance and airflow from the outlet of the scattering unit can be shown, and the scattering bifurcation phenomenon can be displayed more obviously.     

基于DOE的大转矩工况下齿面接触形态优化

结合DFSS创新设计方法及受载齿轮接触仿真分析(LTCA),对某齿轮对大转矩工况下较差的接触形态进行优化,找到影响齿轮接触性能的关键要素及影响程度,并通过DOE实验设计完成齿面接触性能参数的最优化设计,最终,通过实验证明了优化参数的准确性和可靠性。     

刻蚀机装备设计中的序贯试验设计方法研究

450mm晶圆刻蚀机开发中大量应用确定性仿真来模拟腔室内部物理、化学环境,并通过仿真结果指导装备结构的详细设计。为控制仿真试验的采样规模以缩短开发周期,本文详细介绍一种新型的基于采样密度和非线性度的序贯设计方法。此方法通过蒙特卡洛方法,在设计空间中获得采样密度信息,进而对低采样密度区域增加采样点。另外,通过对每个采样的领域进行发掘,以获得采样的梯度和非线性度信息,进而对高度非线性的区域增加采样点。以450mm刻蚀机约束环设计模型和Goldstein-Price模型为背景,采用拉丁超立方和新型序贯设计方法同时采样,以代理模型精度和特征捕捉能力两个角度来对比采样结果的优劣,结果证明,在达到同样精度的前提下,新型序贯设计方法能有效减小采样规模,符合刻蚀装备设计的需要。     

DOE试验设计在选矿工艺参数优化中的应用

针对某公司铁精矿全铁稳定率差的问题,采用DOE试验设计对选矿工艺参数进行优化,以达到考核目标值。通过DOE试验设计方法,确定了各关键因子的调整范围,在此范围内,精矿品位可达到要求值,精矿全铁稳定率可控制在规格范围内。     

Enhancing TRU burning and Am transmutation in Advanced Recycling Reactor

This paper presents about conceptual designs of Advanced Recycling Reactor (ARR) focusing on enhancement in transuranics (TRU) burning and americium (Am) transmutation. The design has been conducted in the context of the Global Nuclear Energy Partnership (GNEP) seeking to close nuclear fuel cycle in ways that reduce proliferation risks, reduce the nuclear waste in the US and further improve global energy security. This study strives to enhance the TRU burning and the Am transmutation, assuming the development of related technologies in this study, while the ARR based on mature technologies was designed in the previous study. It has followed that the provided TRU burning core is designed to burn TRU at 28 kg/TW_thh, by adding moderator pins of B₄C (Enriched B-11) and the Am transmutation core will be able to transmute Am at 34 kg/TW_thh, by locating Am blanket of AmN around the TRU burning core. It indicates that these concepts improve TRU burning by 40-50% than the previous core and can transmute Am effectively, keeping the void reactivity acceptable.