气体化学反应流动的DSMC／EPSM混合算法研究

发展了平衡粒子模拟方法(EPSM),建立了与高温气体化学反应动力学理论相匹配的：EPSM耦合模型,并通过混合参数进行流区的自动识别,将：EPSM方法与蒙特卡罗直接模拟方法(OSMC)结合,构造了可模拟化学反应流动的DSMC／EPSM混合算法。应用该算法对汲及化学反应的二维高超音速竖板绕流流场进行模拟,将结果与DSMC方法的结果进行比较,验证了新算法对求解化学反应流动的可行性。将混合算法的计算效率与DSMC方法的计算效率进行比较,发现混合算法能够大大提高计算效率。     

一类电化学反应的差分解法

对一类电化学反应中的粒子扩散问题提出了一种差分解法。在一个实际例子的数值计算中,得到了电极表面的特质浓度降为零所需要的时间。     

一维Tyson扩散模型行波解的一般性质

本文系统地讨论了一维Ｔｙｓｏｎ扩散模型三种不同类型的行波解的一般性质。     

随机选取法计算化学反应流爆轰过程引起的参数涨落

利用ＲＣＭ（随机选取法）解反应流爆轰问题时,掌握影响流动参数随机涨落的主要因素是选择适当计算参数、保证得到正确结果的关键。各种流动参数的随机涨落相互关联,只需要搞清楚炸药未反应质量分数的随机涨落并做出分析,其它流动参数涨落的情况也就清楚了。给出了影响未反应质量分数涨落的因数,同时还给出了具体算例,检验所得结论的正确性。     

Discrete formulation of mixed finite element methods for vapor deposition chemical reaction equations

The vapor deposition chemical reaction processes, which are of extremely extensive applications, can be classified as a mathematical model by the following governing nonlinear partial differential equations containing velocity vector, temperature field, pressure field, and gas mass field. The mixed finite element (MFE) method is employed to study the system of equations for the vapor deposition chemical reaction processes. The semidiscrete and fully discrete MFE formulations are derived. And the existence and convergence (error estimate) of the semidiscrete and fully discrete MFE solutions are demonstrated. By employing MFE method to treat the system of equations for the vapor deposition chemical reaction processes, the numerical solutions of the velocity vector, the temperature field, the pressure field, and the gas mass field can be found out simultaneously. Thus, these researches are not only of important theoretical means, but also of extremely extensive applied vistas.     

具有表面效应的球形纳米电极颗粒中的反应-扩散-力学全耦合分析

表面效应在纳米电极颗粒中占有主导地位,论文首先建立了锂离子电池充放电过程中考虑表面效应的反应-扩散-力学全耦合模型;然后对比了有无表面效应对锂离子浓度、径向应力和环向应力的影响;最后探讨了反应系数和尺寸效应对浓度和扩散诱导应力的影响.数值结果表明表面效应随着充电时间的增加逐渐减小直至充电结束趋于稳定;表面压效应对本模型的浓度无影响但抑制了扩散诱导应力的增加;较慢的化学反应和较小的纳米电极颗粒尺寸可抑制电极应力的增加.     

化学反应流中分子扩散的二点封闭MCA模型

在化学反应流的概率密度函数(PDF)方法中,对流项和化学反应项都是封闭的,但分子扩散项必须模拟. 现有的分子扩散模型都是唯象的,需要引入外加参数,并难以通过一些基本物理过程的检验. 本文发展了随机映射逼近(mapping closureapproximation, MCA)方法, 解析地从控制方程导出一个封闭的分子扩散模型.该方法考虑两点联合概率密度函数方程,引入空间特征尺度,因此解决了以往映射封闭方法中分子扩散速率无法确定的问题. 数值模拟表明该方法能用于预测标量扩散的速度,以及概率密度函数和条件平均扩散等统计量.     

分形输运的动力学

分形中的反常扩散是输运理论研究的一个热点，但大部分结果都是标度讨论和模拟。本文应用分数阶扩散方程研究多标度分形上的扩散规律，所得结果与文献中的结论完全一致。     

微重力场中液体在带隔板球腔内的晃动

本文讨论微重力场中带球面隔板的球腔内液体晃动问题。选择Legendre函数作为Ritz方法的基函数,计算液体的自由晃动及腔体横向振动激励的受迫振动。计算结果表明,自由晃动频率随隔板位置的下降而趋于升高。液体晃动的动力学效应可用等效的质量—弹簧系统模拟。     

SYNTHESIS AND APPLICATION OF NANOPARTICLES BY A HIGH GRAVITY METHOD

Fast chemical reactions involved in nanomaterials synthesis, polymerization, special chemicals production, reactive absorption, etc., are often difficult to control in terms of product quality, process efficiency and production consistency.After a theoretical analysis on such processes based on chemical reaction engineering fundamentals, an idea to intensify micromixing (mixing on the molecular scale) and mass transfer and therefore to control the process ideally was proposed.By experimental investigations of mass transfer and micromixing characteristics in the Rotating Packed Bed (RPB, or “HIGEE“ device), we achieved unique intense micromixing. This led us to the invention of using RPB as a reactor for the fabrication of nanoparticles (Chen et al., 2000).RPB consists mainly of a rotating packed rotator inside a stationary casing. The high gravity environment created by the RPB, which could be orders of magnitude larger than gravity, causes aqueous reactants going through the packing to spread or split into micro or nano droplets, threads or thin films, thus markedly intensifying mass transfer and micromixing to the extent of 1 to 3 orders of magnitude larger than that in a conventional packed bed.In 1994, the first RPB reactor was designed to synthesize nanoparticles of CaCO3 through multiphase reaction between Ca(OH)2 slurry and CO2 gas, and nanoparticles of 15～30nm in mean size and with very uniform particle size distribution was obtained. In 1997, a pilot-scale RPB reactor was successfully set up for operation, and in 2000, the first commercial-scale RPB reactor for synthesis of such nanoparticles came into operation in China, establishing a milestone in the use of RPB as a reactor for the fabrication of nanomaterials (Chen et al., 2002).Since then, the high gravity method has been employed for the synthesis of inorganic and organic nanoparticles via gas-liquid, liquid-liquid, and gas-liquid-solid multiphase reactions, e.g. inorganic nanoparticles like nanosized CaCO3, TiO2,SiO2, ZnO, Al2O3, ZnS, BaTiO3, BaCO3, SrCO3, Al(OH)3 and Mg(OH)2 flame retardants, and organic nano-pharmaceuticals including benzoic acid, salbutamol sulfate and cephradine. This technology received extensive attention in the field of nanomaterials fabrication and application. Dudukovic et al. commented, “The first large-scale application of RPB as a reactor occurred in China in production of nano CaCO3 by HGRP (high gravity reactive precipitation)of carbon dioxide and lime. Uniformly small particles were made in the RPB due to achievement of a sharp supersaturation interface and very short liquid residence times in the device.“ (Dudukovic et al., 2002). Date et al. said, “HGRP represents a second generation of strategies for nanosizing of hydrophobic drugs. In our opinion, among various methodologies described eariier, supercritical anti-solvent enhanced mass transfer method and HGRP method has potential to become technologies of the future owing to their simplicity, ease of scale-up and nanosizing efficiency“ (Date et al., 2004).As-synthesized nano CaCO3 was employed as a template to synthesize silica hollow spheres (SHS) with mesostructured walls. Characterizations indicated that the obtained SHS had an average diameter of about 40 nm with a surface haviors of Brilliant Blue F (BB), which was used as a model drug. Loaded inside the inner core and on the surfaces of SHS,BB was released slowly into a bulk solution for as long as 1 140min as compared to only 10min for the normal SiO2nanoparticles, thus exhibiting a typical sustained release pattern without any burst effect. In addition, higher BET value of the carrier, lower pH value and lower temperature prolonged BB release from SHS, while stirring speed indicated little influence on the release behavior, showing the promising future of SHS in controlled drug delivery (Li et al., 2004).Nano-CaCO3 synthesized by the high gravity method was also employed as a filler to improve the performance of organic materials. By adding CaCO3 nanoparticles into polypropylene-ethylene copolymer (PPE) matrix, the toughness of the matrix was substantially increased. At a nanosized CaCO3 content of 12 phr (parts per hundred PPE resin by weight),matrix. In the nanosized CaCO3/PPE/SBS (styrene-butadiene-styrene) system, the rubbery phase and filler phase were independently dispersed in the PPE matrix. As a result of the addition of nanosized CaCO3, the viscosity of PPE matrix significantly increased. The increased shear force during compounding continuously broke down SBS particles, resulting in the reduction of the SBS particle size and improving the dispersion of SBS in the polymer matrix. Thus the toughening effect of SBS on matrix was improved. Simultaneously, the existence of SBS provided the matrix with good intrinsic toughness, satisfying the condition that nanosized inorganic particles of CaCO3 efficiently toughened the polymer matrix,thus fully exhibiting the synergistic toughening function of nanosized CaCO3 and SBS on PPE matrix (Chen et al., 2004).As-prepared nano-CaCO3 was blended with TiO2 and other additives to prepare complex master batches for use in the coloring of polypropylene. It was found that the obtained nano-CaCO3 is an excellent pigment dispersant, which can partially replace TiO2 pigments for polypropylene resin coloring. Nano-CaCO3 can prompt the dispersion of TiO2 in polymer matrix, boosting the whiteness of the materials without a negative effect on the UV absorbency of the materials (Guo et al.,2004). Studies on the mechanical properties of nano-CaCO3 toughened epoxy resin composite indicated that impact strength and flexural modulus of the composite improved remarkably when 6wt.% of nano-CaCO3 was added. Surface treatment of nano-CaCO3 by titanate coupling agents significantly improved the dispersibility of nano-CaCO3 in such a high viscous matrix (Li et al, 2005).     

MASS PRODUCTION OF NANOPARTICLES BY HIGH GRAVITY REACTIVE PRECIPITATION TECHNOLOGY WITH LOW COST

Mass production of nanoparticles at low cost has attracted much attention from industrial and academic circles. In this paper, a novel method, the high gravity reactive precipitation (HGRP) technology, of manufacturing CaCO3 nanoparticles, presently scaled-up to an annual capacity of 10,000 tons, is presented. This paper describes the process princ/ple, the process design and experiments on the syntheses of 15-30 nm CaCO3, 30-50 nm SiO2,20-30 nm TiO2, 20-60 nm ZnO, 20-30 nm ZnS, 30 nm SrCO3, 40-70 nm BaTiO3, stick-like nano BaCO3 as well as nano-fibrillar aluminum hydroxide measuring 1-10 nm in diameter and 50-300 nm in length, using liquid-liquid,gas-liquid and gas-liquid-solid reactant systems. The advantage of using the HGRP technology is illustrated by comparison to conventional methods.     

NUMERICAL STUDY ON STEADY STATE THREE-DIMENSIONAL ATMOSPHERIC DIFFUSION OF SULFUR DIOXIDE AND SULFATE DISPERSION WITH NON-LINEAR KINETICS

The aim of the present work is to study the three dimensional, steady state atmospheric diffusion equation for sulfate with its formation by conversion of sulfur dioxide (SO₂) and removal by wet and dry depositions under the general Michaelis—Mcnlen process. The equations governing the non-linear diffusion process are numerically solved using an alternating direction implicit finite difference scheme. It has been shown that in the case of wet deposition, the percentage decrease in sulfate level is rapid over the range 0 < X ≤ 0.67 (X = dimensionless longitudinal distance) as compared to that of the case of dry deposition. Further, sulfate levels remain higher at ground level for X = 1.0 but its levels remain lower at ground level for X = 0.3 and 0.1. Wet removal is found to be more dominant than dry removal in the far off regions of the point source. The fallout of deposits is significant near the source and at the far off lateral distance.