湿浸法制备活性组分非均匀分布负载型催化剂过程的计算机模拟

对活性组分非均匀分布的负载型催化剂的湿浸法制备过程进行了计算机模拟,其模拟程度可适用于任意多个活性组分的浸渍。发现单组分浸渍时,通过控制浸渍时间可获得活性组分由薄到厚的蛋壳型分布和均匀分布,但通过预浸渍吸附至一定分布后,再在空白溶液中浸渍洗脱,控制洗脱条件也可获得蛋黄、蛋白型的分布;加入竞争吸附剂,进行双组分及多组分浸渍,通过控制浸渍溶液性质及浸渍时间可获得各种类型的活性组分分布,诸如蛋壳型、蛋白型、蛋黄型和均匀型。通过对制备过程参数(如竞争吸附剂的选择、各组分有效扩散系数、初始浓度、吸脱附速率常数等)与活性组分分布形式之间关系的分析,可实现对任一分布形式的催化剂的制备过程参数的优化。这对实际制备催化剂具有指导意义。     

Errors associated with swelling in the analysis of polymer-solvent diffusion measurements

Sorption curves are generated from a mathematical model which includes the influence of the polymer swelling for unsteady-state sorption of a vapor or liquid by a polymer. To investigate the simultaneous effects of the specific volumes of the polymer-penetrant pair and the difference between the final and initial equilibrium concentrations on the sorption curves, statistical experimental design approach is used. Simulation results obtained from the numerical solution of model equations are utilized to estimate the error that would occur if one simply evaluates the diffusion coefficient using the traditional formulas derived from the analytical solution of the sorption equation. An empirical expression is developed that describes the effects of the difference between the final and initial equilibrium concentrations and the specific volumes of the polymer and the penetrant on the magnitude of error in diffusivity associated with the use of one of these traditional formulas so called the initial slope method. The predictive ability of the regression model is tested by performing additional simulations not used in the regression analysis.     

Capillary jet instability under the influence of gravity

The focus of this paper is on the effect of gravity stretching on disturbed capillary jet instability. Break-up and droplet formation under low flows are simulated using finite difference solution of a one-dimensional approximation of disturbed capillary jet instability chosen from the work by Eggers and Dupont (J. Fluid Mech. 155 (1994) 289). Experiments were conducted using water and aqueous glycerol solutions to compare with simulations. We use a gravity parameter, G, which quantifies gravity stretching by relating flow velocity, orifice size and acceleration and is the reciprocal of the Froude number. The optimum disturbance frequency was found to be inversely proportional to G. However, this relationship appears to be complex for the range of G's investigated. At low G, the relationship between and G appears to be linear but takes on a weakly decaying like trend as G increases. As flows are lowered, the satellite-free regime decreases, although experimental observation found that merging of main and satellite drops sometimes offset this effect to result in monodispersed droplet trains post break-up. Viscosity did not significantly affect the relationship between the disturbance frequency and G, although satellite drops could be seen more clearly close to the upper limit for instability at high G's. It is possible to define regimes of satellite formation under low flows by considering local wavenumbers at the point of instability.     

Simulation of reverse flow operation for manipulation of catalyst surface coverage in the selective oxidation of ammonia

A mathematical model has been developed for the simulation of the ammonia oxidation in a reverse flow reactor. Computer simulations were carried out with a kinetic scheme, based upon elementary reaction steps. Aim was to explore the potential of a reverse flow reactor for selective oxidation of NH₃ to produce either N₂, NO, or N₂O via a dedicated operation procedure. Therefore, the conversion of NH₃ and the selectivity toward N₂, NO, or N₂O, were compared for a reverse flow operation and a steady state, once-through operation.A new operation concept of reverse flow operation in combination with a periodically lower feed concentration is proposed. The novel reactor concept shows a better performance compared to normal reverse flow operation and to steady state, once-through operation. The results indicate that reverse flow operation can be applied for manipulation of conversion and selectivity. A periodically lower feed concentration may increase the conversion, even up to levels that exceed the steady state value.     

应文明地选择祭扫的对象化方式

人是用语言和自然物来表达情感和思想的对象性动物,但人应时刻用正确的理性来规范自己的情感和思想,不要随意对象化。烧纸、物不但浪费物质财富,而且会污染空气,经常引起火警阵阵。人烧纸、物等纯粹是自己一厢情愿表达情感的方式,因为鬼神观念是人自己创造的虚幻产物,即使用所谓佛教的众生六道轮回的理论稍加分析,也不该如此。人应该善待或善用自己不容易创造的物质财富,文明地选择祭扫的对象化方式。     

反拱法碳纤维加固RC梁的数值模拟分析

采用动力设备将钢筋混凝土梁向上反拱一定的弧度,然后在梁的下部外贴碳纤维布（CFRP）,待碳纤维布养护完全后,卸载,此时后加的碳纤维布与原钢筋混凝土梁同时进入工作状态。作者采用分析软件ANSYS模拟此过程,通过与直接用碳纤维布加固RC梁进行比较,得出反拱法加固RC梁能有效提高其承载能力,对类似工程具有一定的借鉴意义。     

水力旋流器内清水流场空气柱的三维数值模拟

本文依据计算流烙动力学（CFD）的计算方法,利用Fluent软件对带有空气柱的固-液分离用水力旋流器内清水流场进行了三维数值模拟研究。文章中首次采用“mixture”模型对空气柱进行模拟,模拟所得的流场与实测结果作对比,证明效果良好。本文的工作对进一步研究旋流器固-液分离现象提供了一定的基础和参考。     

Matlab中的代数环问题及其消除方法

本文以免疫PID的SimuLink模型及其S函数为例引出代数环问题,分析了代数环的基本概念,指出了代数环对控制系统仿真的巨大危害,最后结合实际提出了几种消除代数环的方法。结果表明,代数环消除后提高了系统的仿真精度和运行速度。     

鱼雷静不稳定状态下纵向三回路过载控制与仿真研究

静不稳定控制技术作为现代航空航天、水中兵器主动控制技术,在近些年逐渐成为研究热点。本文针对某静不稳定鱼雷,建立了纵向运动模型,运用最优控制理论设计了俯仰通道三回路过载控制系统,最后对设计出的控制器进行了特征点控制系统仿真。结果说明,三回路过载控制方法能较好地控制静不稳定鱼雷。     

试论当代大学和谐校园的建设

指出了和谐校园建设是构建和谐社会的重要组成部分,首先阐述了建设大学和谐校园的重要意义,简析了目前造成大学不和谐的若干问题,并在此基础上提出了加强建设当代大学和谐校园的主要途径。