CFD modeling of pilot-scale pump-mixer: Single-phase head and power characteristics

The present work involves single-phase computational fluid dynamics (CFD) simulations of continuous flow pump-mixer employing top-shrouded Rushton turbines with trapezoidal blades. Baffle—impeller interaction has been modeled using sliding mesh and multiple reference frame approaches. Standard k-ε model has been used for turbulence modeling. Several CFD runs representing different combinations of geometric and process parameters have been carried out. Results of CFD simulations have been used to find out two macroscopic performance parameters of pump-mixer—power consumption and head generated by the impeller. The simulation results have been compared with the experimental data obtained on a pilot-scale setup. Good agreement between CFD predictions and experimental results is observed. In most cases, sliding mesh approach is found to perform better than multiple reference frame approach. Details from CFD simulations have been used to have an insight into the pumping action of the impeller.     

Novel positive‐working aqueous‐base developable photosensitive polyimide precursors based on diazonaphthoquinone‐capped polyamic esters

Novel positive‐working aqueous‐base developable photosensitive polyimide (PSPI) precursors based on partially diazonaphthoquinone (DNQ)‐capped polyamic esters bearing phenolic hydroxyl groups and a DNQ photosensitive compound (PIC‐3) were developed. The partially DNQ capped polyamic esters were prepared from an esterification reaction of 1,2‐naphthoquinone diazide‐5‐sulfonyl chloride with the polyamic esters. The partially DNQ capped polyamic esters decreased the dark film loss effectively in the aqueous‐base developer and were able to make thicker film resists compared to the uncapped polyamic esters. The 25 mol % DNQ‐capped BisAPAF–PMDA polyamic ester and BisAPAF–ODPA polyamic ester containing 25 wt % PIC‐3 photosensitive compound showed a sensitivity of 176 and 185 mJ/cm², and a contrast of 1.68 and 1.02, respectively, in a 3‐μm film with 1.25 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 5 μm was obtained from both PSPI precursor compositions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2293–2300, 2003     

降温速率对Ba0.92Ca0.08TiO3 PTCR陶瓷室温电阻率"反常"现象的影响

通过系统研究烧结工艺对BaO92Ca0.08TiO3电阻正温度系数(possitive temperature coefficient resistance，PTCR)陶瓷的影响，在晶粒生长过程中分析液相在晶界中的分布。着重研究降温速率对PTCR室温电阻率的影响。发现在1300～1150℃温区内，当降温速率大于15℃／min时，出现随降温速率增加，室温电阻率增大的“反常”现象。根据液相在晶界区分布随降温速率的变化规律，对这种“反常”进行解释。     

掺锰BaTiO3 PTCR陶瓷的电子顺磁共振研究

利用电子顺磁共振（EPR）方法对Mn掺杂的BaTiO3 PTCR陶瓷在120－450K的温度范围内进行了研究，研究结果表明：高自旋Mn^2 离子的6重谱线非常明显，表征谱线位置的g因子为2．009 9,Mn^2 离子信号弱弱与BaTiO3晶体结构密切相关，Mn^2 离子信号的温度分布呈U型，即在三方相和立方相时，信号强度较强，而在四方相和斜方相时信号很弱，这是因为在四方相和斜方相中，由于BaTiO3晶体结构的扭曲和畸变，导致Mn^2 和Vo空位缔合生成Mn^2 -Vo复合缺陷，未成对电子的消失以及复合缺陷n^2 -Vo的生成最Mn^2 在四方相和斜方相（200－380K）消失的主因，实验中没有发现Mn^3 和Mn^4 的信号，而与实验的环境条件一致，掺Mn后样品Curie点的漂移可能是Mn进入晶格的一个判据，此外，由于试样的n(Ba)/n(Ti)=1，因而没有发现钡空位VBa及其它的复合缺陷（如：VBa-Mn^2 ,Mn^3 -Vo,La^3 -Mn^3 等），Mn^2 离子等电子陷阱的生长是Curie温度处电阻骤然增加的主要原因。     

水泥企业常用热电偶的使用与维护

测温元件——热电偶热的电势大小仅和两金属的材料及两结合点的温度有关．鉴于此因素．适当的维护和维修可延长其使用寿命，减少生产成本。针对不同测量系统和不同工艺要求，介绍了四种水泥企业最常用的热电偶以及安装热电偶时所需注意事项。根据生产实践，重点介绍了热电偶的常见故障及其维护与维修方法。     

刹车盘结构对车轮及整车流场的影响

为研究车轮刹车盘结构对旋转车轮和整车流场气动特性的影响,针对是否存在刹车盘两种情况分别建立等比例模型,采用可实现的k-ε两方程模型计算,对比分析气动升、阻力因数,表面压力因数及整体与局部流场,发现刹车盘结构在简化车体上对车轮局部和整车流场都具有突出影响,指出在整车气动特性模拟中刹车盘存在的必要性.进一步进行计算模型选择的研究,发现旋转壁面模型与多坐标参考系(Multiple Reference Frame,MRF)模型对旋转车轮的流场特性模拟结果有差异,在近车轮区域表现尤为明显.     

汽车发动机冷却风扇仿真方法对比

对比多参考坐标系(Multiple Reference Frame,MRF)模型和滑移网格模型(Sliding Mesh Model,SMM)在分析中的差异,分别应用FLUENT中的三维N-S方程和RNG湍流模型,对发动机冷却风扇的静止和旋转区域进行数值模拟,得到流道内空气的质量流量及风扇叶片表面的压力和速度矢量分布.SMM的结果更接近真实结果;根据SMM得出的结果说明MRF模型在工程领域的应用.     

Experimental Evaluation of the Acceptor-States Compensation in Positive-Temperature-Coefficient-Type Barium Titanate

Experimental evidence shows that the acceptor-state levels in Sb-doped positive-temperature-coefficient-type BaTiO₃ are compensated up to a critical acceptor-state density. Using the slope of the natural logarithm of the resistivity with respect to 1/ T , instead of maximum resistivity as a measure for the acceptor-state density, it is possible to estimate this critical value. The value obtained (4.2 × 10¹⁷ m⁻²) is believed to be the first reported estimate based on experimental data. It is in good agreement with the estimate of 6 × 10¹⁷ m⁻² (first reported by Jonker) obtained from the spontaneous polarization of BaTiO₃. This shows that the ferroelectric behavior of BaTiO₃ is indeed a feasible explanation for the low resistivity below the Curie point, as proposed by Jonker.     

Dynamic output feedback control of a flexible air-breathing hypersonic vehicle via T–S fuzzy approach

By utilising Takagi–Sugeno (T–S) fuzzy set approach, this paper addresses the robust H_∞ dynamic output feedback control for the non-linear longitudinal model of flexible air-breathing hypersonic vehicles (FAHVs). The flight control of FAHVs is highly challenging due to the unique dynamic characteristics, and the intricate couplings between the engine and fight dynamics and external disturbance. Because of the dynamics’ enormous complexity, currently, only the longitudinal dynamics models of FAHVs have been used for controller design. In this work, T–S fuzzy modelling technique is utilised to approach the non-linear dynamics of FAHVs, then a fuzzy model is developed for the output tracking problem of FAHVs. The fuzzy model contains parameter uncertainties and disturbance, which can approach the non-linear dynamics of FAHVs more exactly. The flexible models of FAHVs are difficult to measure because of the complex dynamics and the strong couplings, thus a full-order dynamic output feedback controller is designed for the fuzzy model. A robust H_∞ controller is designed for the obtained closed-loop system. By utilising the Lyapunov functional approach, sufficient solvability conditions for such controllers are established in terms of linear matrix inequalities. Finally, the effectiveness of the proposed T–S fuzzy dynamic output feedback control method is demonstrated by numerical simulations.