Effect of free stream angle on mixing performance of hydrogen multi-jets in supersonic combustion chamber

The fuel mixing process within the combustion chamber is a critical procedure for advance of scramjet engine. In current study, the influence of free stream angle on the fuel mixing process of multi jets was thoroughly investigated. This research attempts to applied computational technique to disclose the structure of multi-fuel jets when the supersonic air stream is not normal to the jet direction. The effect of both positive and negative supersonic free stream on the diffusion and penetration of multi-hydrogen jets is fully described. The attention of this research is the flow structure of the multi jets and their interaction in the presence of different free stream angle. Our results indicate that the positive free stream angle expands the mixing zone in the downstream while the negative angle of free stream limited jet distribution inside the combustor. Our results show that mixing efficiency increase approximately 50% when the angle of free stream augments from +20° to −20°. According to our findings, mixing efficiency surges up to 17% when the jet spaces are increased from 4Dj to 10 Dj.     

Mass transport limitations in microchannel methanol-reforming reactors for hydrogen production

The potential of methanol reforming systems to greatly improve productivity in chemical reactors has been limited, due in part, to the effect of mass transfer limitations on the production of hydrogen. There is a need to determine whether or not a microchannel reforming reactor system is operated in a mass transfer-controlled regime, and provide the necessary criteria so that mass transfer limitations can be effectively eliminated in the reactor. Three-dimensional numerical simulations were carried out using computational fluid dynamics to investigate the essential characteristics of mass transport processes in a microchannel reforming reactor and to develop criteria for determining mass transfer limitations. The reactor was designed for thermochemically producing hydrogen from methanol by steam reforming. The mass transfer effects involved in the reforming process were evaluated, and the role of various design parameters was determined for the thermally integrated reactor. In order to simplify the mathematics of mass transport phenomena, use was made of dimensionless numbers or ratios of parameters that numerically describe the physical properties in the reactor without units. The results indicated that the performance of the reactor can be greatly improved by means of proper design of catalyst layer thickness and through adjusting feed composition to minimize or reduce mass transfer limitations in the reactor. There is not an effective method to reduce channel dimensions if the flow rate remains constant, or to reduce fluid velocities if the residence time is kept constant. The rate of the reforming reaction is limited by mass transfer near the entrance of the reactor and by kinetics further downstream, when the heat transfer in the autothermal system is efficient. Finally, the criteria that can be used to distinguish between different mass transport and kinetics regimes in the reactor with a first-order reforming reaction were presented.     

AC-13级配钢渣沥青混合料粘弹塑本构模型研究

为了研究钢渣沥青混合料非线性粘弹塑性变形特性,提出Schapery模型与改进Swchartz模型组合的积分型粘弹塑本构模型。采用钢渣替换AC-13级配中粒径2.36 mm以上的石灰石粗骨料,制作得到钢渣沥青混合料试件。设计并开展一系列的单轴压缩蠕变实验,通过应力递增蠕变回复实验,获得不同应力条件下材料的弹性、粘弹性应变和粘塑性应变,进而拟合确定本构模型参数。利用0.4 MPa、1.0 MPa下的蠕变回复实验验证模型有效性。结果表明,模型不仅能准确刻画钢渣沥青混合料蠕变过程中的弹性、粘弹性与粘塑性变形,还可用于预测不同应力水平下钢渣沥青混合料蠕变变形规律。     

Improved indoor environment through optimised ventilator and furniture positioning: A case of slum rehabilitation housing,Mumbai, India

This study optimized the ventilator and furniture location of a tenement unit in a low-income urban habitat to obtain maximum experiential indoor environmental quality (e-IEQ) over the breathing zone. Hypothetical interior layouts using a combination of the two design parameters of ventilator location and bed position were generated for optimizing the design layout. This layout could promote maximum indoor airflow and minimum indoor air temperature and contaminant concentration. In this study, an improved indoor environment is hypothesized to be attainable through improved natural ventilation and thermal performance in the occupied zones. A sequential methodology involving “parametric design modeling–computational simulation–multiobjective optimization–multicriteria decision making”-based framework was selected. Results exhibited that the currently designed tenement unit had a poor indoor environment, whereas the hypothesized iterated layout “optimized design layout, scenario 3 (ODL 3)” derived from the optimization and decision-making algorithm performed effectively in providing e-IEQ. An increase in experiential indoor air velocity by 0.2 m/s and a decrease in temperature by 2 °C were observed over the monitoring point in the ODL 3 considering the existing scenario. Therefore, this study can find a way toward the development of sustainable habitat design guidelines under upcoming slum redevelopment policies across the nation.     

高pH值完井液中钛合金管材的腐蚀行为研究

基于高温高压腐蚀速率和原位电化学测试,并结合分子动力学模拟和第一性原理计算,探讨了钛合金(TC4)管材在高pH值完井液中的腐蚀行为,以及钝化膜的热力学稳定性。结果表明:TC4钛合金在180℃的高pH值磷酸盐完井液中的腐蚀极为严重,其均匀腐蚀速率高达0.4429mm/a;在高pH值磷酸盐完井液中,TC4钛合金的腐蚀为阳极反应过程控制,随着温度的升高,其腐蚀电位、腐蚀产物膜的膜阻和极化电阻显著降低,腐蚀反应的热力学驱动力增大、动力学阻力降低,腐蚀电流密度显著升高;在碱性溶液中,TiO_2钝化膜的钛氧键发生不同程度断裂,并且随着温度升高、碱性增强,TiO_2与溶液的界面结合能逐渐增大,钝化膜的热力学稳定性明显降低;在碱性焦磷酸钾溶液中,TiO_2钝化膜均可与K_2HPO_4、K_3PO_4反应生成疏松多孔的KTiOPO_4腐蚀产物膜,但TiO_2与K_3PO_4反应的热力学倾向更大。     

Viscoelastic behaviors and drying kinetics of different aqueous gelcasting systems for large Nd: YAG laser ceramics rods

Large and nondeforming Nd: YAG ceramic prepared by wet forming is of great importance as gain medium to obtain high-power solid-state lasers. However, it is difficult to achieve high-quality laser ceramics due to insufficiency of the in-depth understanding of transformation mechanism of gels viscoelasticity and effective control means during drying process. In this work, the rheological behaviors, viscoelastic characteristics, and mechanical strengths in classical acrylamide (AM) and novel Isobam (PIBM) gelcastings were systematically compared to explore the suitable route for the large-sized 2% Nd: YAG transparent ceramics with high aspect ratio (>10). AM system exhibited a higher complex viscosity (1.82 × 10⁵ Pa s), a shorter gel time (92.9 seconds), and a higher flexural strength (about 24.46 MPa) than PIBM system, and especially its ability to quickly gel was beneficial to the homogeneity of green body. In addition, the order of drying rates of wet gels in four drying media was observed as follows: 55℃ hot air> ethanol> solid desiccant> PEG-11000 and the moisture diffusion coefficients were calculated and simulated to offer the deep consideration of drying kinetics. The “ethanol + 55℃ hot air” was regarded as an effective composite drying method to eliminate defect and to achieve φ8 mm × 160 mm Nd: YAG ceramic with the in-line transmittance of 83% @1064 nm. Therefore, not only the cognition of gel process, but also the defects control strategy is proposed. More importantly, this work greatly promotes the application of wet forming and laser ceramics in high-power lasers.     

Interaction of two in-line bubbles of equal size rising in viscous liquid

The interaction of bubbles is the key to understand gas–liquid bubbling flow. Two-dimensional axis-symmetry computational fluid dynamics simulations on the interactive bubbles were performed with VOF method,which was validated by experimental work. It is testified that several different bubble interactive behaviors could be acquired under different conditions. Firstly, for large bubbles(d: 4, 6, 8, 10 mm), the trailing bubble rising velocity and aspect ratio have negative correlations with liquid viscosity and surface tension. The influences of viscosity and surface tension on leading bubble are negligible. Secondly, for smaller bubbles(d: 1, 2 mm), the results are complicated. The two bubbles tend to move together due to the attractive force by the wake and the potential repulsive force. Especially for high viscous or high surface tension liquid, the bubble pairs undergo several times acceleration and deceleration. In addition, bubble deformation plays an important role during bubble interaction which cannot be neglected.     

Parametric optimization of packed bed for activated coal fly ash waste heat recovery using CFD techniques

Coal fly ash is an industrial solid waste generated from coal preparation during the processing and cleaning of coal for electric power generation. Comprehensive investigation on the reutilization of waste heat of activated coal fly ash is of great economic significance. The method of recovering the waste heat, proposed in this study,is the transfer of heat from activated coal fly ash to gas with the movement of air using the packed bed, providing valuable energy sources for preheating the raw coal fly ash to reduce the overall energy consumption. The investigation is carried on the heat transfer characteristics of gas–solid(activated coal fly ash) phases and air temperature fields of the packed bed under some key conditions via computational fluid dynamics. A two dimensional geometry is utilized to represent key parts of packed bed. The distribution mechanism of the temperature field for gas phase is analyzed based on the transient temperature contours at different times. The results show that the obtained rule of gas–solid heat transfer can effectively evaluate the influences of operating parameters on the air temperature in the packed bed. Simultaneously, it is found that no temperature differences exist in the hot air at the outlet of the packed bed. The investigation provides guidance for the design and optimization of other similar energy recovery apparatuses in industries.     

催化裂化催化剂形貌分析方法的建立

结合显微镜观察,通过分析毫米级颗粒、微米级Duke粒子及催化裂化催化剂,研究动态数字图像分析仪CamsizerX2分析颗粒形貌的合理准确性。考察分散方式、分散压力和记录颗粒数量因素的影响,建立了催化裂化催化剂球形貌分析方法。     

用于阀芯类零件去毛刺的磁极板优化设计与实验研究

目的 为解决阀芯类零件节流边毛刺去除不均匀和效率低下的问题，对磁极板尺寸和曲率进行规律性研究和实验验证。方法 首先，用Maxwell仿真软件对磁极板的各个参数进行规律性仿真，得出合适的磁极板尺寸;其次，为提高加工区域的磁感应强度值，设计了曲面磁极板，并对其相关参数进行仿真;最后对优化后的装置进行磁感应强度测试，并使用液体磁性磨具对45钢和阀芯棱边毛刺进行去除实验。结果 根据仿真结果发现，磁极板长度比工件大20 mm时，工件轴向磁场分布最均匀，磁极板厚度对磁场影响较小，磁极板宽度应根据加工间隙进行选择。曲面磁极板可以加强加工区域的磁感应强度值，曲率半径越小，加工区域获得的磁感应强度值越大，其中半圆形磁极板效果最佳。对装置的磁感应强度测试也表明，将工件置于磁场中后，其表面磁感应强度值最高达600 mT左右，满足加工需求。最后通过加工实验发现，在转速为500 r/min的条件下，阀芯节流边的毛刺去除效果理想，且轴向加工均匀。结论 该装置可以对阀芯这类导磁性回转类零件产生良好的加工效果。