纳米流体在生物组织内有效扩散系数的Monte Carlo模拟

基于肿瘤热疗研究方向,将生物组织提炼成多孔介质,采用Monte Carlo方法对纳米流体在生物组织内的有效扩散系数进行了数值模拟,并分析了各种不同多孔结构（圆形、椭圆形）、不同大小、不同排列方式等结构因素对有效扩散系数的影响。发现纳米微粒在多孔介质内的扩散过程中存在“口袋效应”。模拟结果与理论公式相符,并通过实验数据验证了该方法的正确性。     

纸张干燥中湿分扩散系数的估算

纸张干燥过程涉及到多孔介质的热质传递,如何确定质量扩散系数是所建立的多孔物料湿分扩散模型能否进行数值计算的关键。按Liukov公式将湿分扩散系数视为含湿质量分数的非线性函数,在恒温下进行纸张干燥实验,通过比较湿分蒸发质量的测量值与理论计算值,采用多变量寻优的方法对多孔介质一维情况下的湿分扩散系数进行估算,得到了实验条件下的纸张湿分扩散系数的计算公式。并进一步确定了纸张中的湿分扩散系数与含湿质量分数和温度之间的函数关系式。     

Estimation of surface diffusion coefficient in liquid phase adsorption

An estimation procedure of surface diffusion coefficient, D_s, in liquid phase adsorption was proposed. The procedure is based on a restricted diffusion model, in which D_s is correlated with molecular diffusivity by considering a restriction energy due to an adsorptive interaction between adsorbates and adsorbents. In some adsorption systems, D_s of different adsorbates could be calculated with an error less than about 50% from only one datum of each adsorption equilibrium constant. Irrespective of temperature, the procedure, can be applied for the estimation of D_s even in a wide range of D_s of about 4 orders of magnitude.     

Prediction of the effective diffusion coefficient in random porous media using the finite element method

A finite-element-based method is presented for evaluating the effective gas diffusion coefficient of porous solids. Using this method, the 3-D micro-scale geometries of the porous solids are constructed under the ANSYS platform by the parametric code; the relation between effective gas diffusivity and micro-scale features of random-distributed porous solids is established. The results show that in random-distributed pore media, there is a percolation threshold ε _p, and this percolation threshold decreases with increasing coordination number of the pore network. The relationship between the effective diffusivity and porosity is strongly nonlinear when the porosity, ε, is less than a certain value ε _L ; for ε > ε _L , the relationship becomes quasi-linear. This dividing point ε _L decreases with increasing coordination number. The larger the coordination number of the pore network, the higher the effective gas diffusivity. Based on the simulation results and observations, a formula relating the effective diffusion coefficient with porosity is proposed.     

Concentration-dependent molecular diffusion coefficient of gaseous ethane in liquid toluene

We report new experimental data on concentration-dependent molecular diffusion coefficient of ethane in toluene at temperatures ranging from 21 to 125°C and pressures up to 4.14 MPa. An analytical model has also been developed for estimation of the diffusion coefficient utilizing the experimental data of the interface velocity as a result of swelling and the rate of gas dissolution in the liquid phase. It is shown that the diffusion coefficient of ethane in toluene is dependent on the initial mass fraction of the gaseous component in the liquid. In addition, the effect of concentration dependency of the molecular diffusion coefficient on diffusive mass flux is quantified. The results reveal that the assumption of a constant diffusion coefficient introduces ~10–60% error in calculation of diffusional mass transfer flux. The developed methodology finds application in estimation of the concentration-dependent molecular diffusion coefficient of gases in liquids.     

分形多孔介质中气体的非稳态扩散

通过引入平均修正系数修正Fick第二扩散定律得到了描述分形多孔介质气体非稳态扩散的理论方程。基于“塞状流”扩散实验法建立了分形多孔介质非稳态扩散实验系统,对3个孔隙结构不同的分形多孔介质样品进行了非稳态扩散实验,通过实验对理论方程进行验证和修正。结果表明,Fick第二扩散定律不适用于分形多孔介质中气体非稳态扩散,分形多孔介质中气体非稳态扩散存在一定规律,且多孔介质孔隙结构不同其扩散规律不同。     

应用隔膜池及分形方法测算金黄杆菌在土壤中的有效扩散系数

细菌在土壤中的扩散过程在微生物修复中具有重要作用。本文针对地下水饱和土壤,提出了利用土壤膜隔膜池的扩散实验方法,建立了土壤膜池理论和分形理论测算细菌扩散系数的理论基础。通过KCl扩散实验标定了隔膜池常数 β_KCl＝1.45 cm^-2,对于大体积的细菌通过多孔土壤膜的有效扩散面积小于KCL的有效扩散面积,本文利用分形理论模型计算得到细菌扩散的膜池常数 β_bacteria=0.92 cm^-2。土壤的曲折因子根据分形模型计算得到, τ＝3.17。通过KCl和细菌的扩散实验,并利用分形理论模型,最终求得了细菌在土壤中的有效扩散系数为 D_bacteria,eff＝5.18×10-7 cm^2·s^-1。     

On the mathematics of time-dependent apparent chloride diffusion coefficient in concrete

This paper provides an improved mathematical analysis of chloride penetration into concrete employing a time-dependent diffusion coefficient for the solution of Fick's second law of diffusion. In the paper the possible errors caused by the application of oversimplified mathematical expressions used in some models for the evaluation of service life of reinforced concrete structures are discussed. The results from this mathematical analysis demonstrate that some models based on the oversimplified error function complement (ERFC) solutions may easily overestimate the service life by orders of magnitude, especially when the age factor is high. Some chloride profiles after up to 10 years' field exposure were used to compare the oversimplified with the improved models. The results show that both the oversimplified and the improved models fairly well predict the 10 years' chloride ingress in Portland cement concrete, but the oversimplified ERFC model significantly underestimates the chloride ingress in concrete with fly ash.     

镀层中基体金属扩散系数的测定

铜在防渗铜镀层中的扩散系统是评价镀层防渗铜能力的重要参数。采用电子显微探针法,“俣野”数值方法推导出扩散系数。并分析了铜在柱状和块状镍镀层中的扩散系数。     

氨基酸扩散系数的分子动力学模拟

采用分子动力学模拟的方法模拟了298. 15 K正则系综下甘氨酸、丙氨酸等12种氨基酸在水中的扩散过程，扩散系数的计算采用微分-区限变分法。计算结果表明：相同浓度下按不同分子数样本计算得到的扩散系数有较大差别，且分子数越多则模拟结果越接近于实验值。5种氨基酸在水中的扩散系数与文献值相对比，误差小于7%。还用同样的方法模拟了氧气在水中的扩散过程，模拟结果与实验结果吻合也较好。实验表明采用分子模拟手段可以获得具有工业应用价值的扩散系数，从而有助于计算传质学的发展。     

磷石膏制多孔集料混凝土的研究

将云南磷石膏脱水筛分后水化造粒制成多孔集料,再与425水泥、砂和水混合配制成混凝土,研究了集料包壳、减水剂和养护方式对混凝土强度的影响。结果显示,集料不包壳、不加减水剂和采用湿养护,混凝土的抗压强度为5.17 MPa,可用作非承重墙体材料;用325水泥对磷石膏集料进行1∶4包壳处理,加2%聚羧酸减水剂,采用干养护,混凝土的抗压强度可提高至17.32 MPa,达到了承重墙抗压强度≥10 MPa的国家标准,可替代黏土砖用作承重墙体材料。     

Determination of chloride diffusion coefficient of concrete using open-circuit potential measurements

The rate of chloride ion ingress into concrete is of great importance for the performance of reinforced concrete structures exposed to chloride-contaminated environments. The service life of reinforced concrete structures subjected to such exposure conditions is closely related to the rate of chloride ion diffusion through the concrete. This paper presents the determination of the apparent chloride diffusion coefficient of concrete using open-circuit potential measurements. The chloride diffusion coefficients obtained are in the range of 6.4×10⁻⁸ to 12.4×10⁻⁸ cm²/s for a simulated seawater tidal condition, which is quite consistent with those reported in the literature. This indicates that open-circuit potential measurements can be considered as an approximate but simple method of assessing the diffusivity of chloride through concrete. Limited with the testing conditions and the characteristics of concrete used, results indicated that the time necessary for corrosion initiation of concrete with a cover depth of 7 cm ranges from 3 to 6 years for the seawater exposure, whereas it is only 1.5 years for a 3% sodium chloride exposure.     

Influence of traversing crack on chloride diffusion into concrete

This study examined the effects of traversing cracks of concrete on chloride diffusion. Three different concretes were tested: one ordinary concrete (OC) and two high performance concretes with two different mix designs (HPC and HPCSF, with silica fume) to show the influence of the water/cement ratio and silica fume addition. Cracks with average widths ranging from 30 to 250 μm, were induced using a splitting tensile test. Chloride diffusion coefficients of concrete were evaluated using a steady-state migration test. The results showed that the diffusion coefficient of uncracked HPCSF was less than HPC and OC, but the cracking changed the material behavior in terms of chloride diffusion. The diffusion coefficient increased with the increasing crack width, and this trend was present for all three concretes. The diffusion coefficient through the crack D_cr was not dependent of material parameters and becomes constant when the crack width is higher than  80 μm, where the value obtained was the diffusion coefficient in free solution.     

分形多孔介质的孔隙特性对气体扩散的影响

采用随机行走方法建立了分形多孔介质生成模型,生成的颗粒在形貌上与真实多孔颗粒接近,且能够反映其固有分形特征。在此模型基础上,根据经典分子动理论建立扩散控制方程,对气体在多孔介质中的扩散进行数值模拟。分析了比表面积、平均孔径、孔隙率等孔隙特性参数对扩散的影响,获得了分形多孔介质中气体扩散系数与平均孔径的函数关系。结果表明,扩散系数随平均孔径的增大以幂函数形式增大,相应的指数表征扩散系数对平均孔径的敏感度,其值随孔隙率的增大呈线性减小。     

多孔介质的孔隙特性对气体扩散过程影响的直接数值模拟

引言多孔介质内的扩散过程广泛存在于化工、能源、环境和生物等领域,例如石油天然气开采、污水处理、填充床化学反应、催化剂和生物组织内的质量传递等,使得多孔介质内传质现象的研究尤为重要[1-2]。多孔介质由于结构和形状各异,难以有准确、有效且简单的描述方法,因而研究变得极为     

脂肪酸在甲基丙烯酸异丁酯凝胶中扩散系数的估测

采用分散质分子染色、跟踪手段,对游离脂肪酸分子在甲基丙烯酸异丁酯高分子凝胶体系中有效扩散系数进行测定和估算,实验测得有效扩散系数为10-11 m2/s数量级范围,处于估测范围之内。同时对比了分散质分子在纯液相中的自由扩散系数,并分析了凝胶体系中脂肪酸分子的扩散机制。结果表明:利用染色、跟踪定量法对大分子分散介质在凝胶体系中扩散行为的研究和有效扩散系数的估测具有可行性。     

动态光散射法测定凝胶中大分子有效扩散系数

引　言凝胶广泛应用于生化分离和医学材料等领域 ,其中溶质分子在凝胶中的扩散特性尤为关键[1] 凝胶中溶质分子有效扩散系数的测定方法主要有扩散法[2 ]、荧光恢复法[3]、强制瑞利散射法[4 ]、全息衰减法[5 ]和动态光散射法 (ＤＬＳ) [6～ 8],后者一般用于较软且透明的凝胶 前人在用ＤＬＳ法测定凝胶中溶质分子的扩散系数时均忽略凝胶结构的非均匀性 ,具有较大的局限 本文在处理含大分子凝胶体系的ＤＬＳ数据时 ,在考虑凝胶结构的非均匀性基础上提出了遍历介质非均匀校正法 ,并以溶菌酶在聚丙烯酰胺 (ＰＡＡ)凝胶中的扩散为例 ,验证了该方…     

Kinetic Correlation for the Hindered Diffusion of Proteins in a Porous Packing Column*

Abstract Hindered diffusion of proteins in a porous packing plays an important role in proteinchromatographic purification.The HETP method was adopted to analyze the influence of axialdispersion, film mass transfer and hindered diffosion in the porous packing employing a size-exclusionchromatography(SEC)process.The retention behavior with eight proteins of different relativemolecular mass was experimentally detected with a commercial SEC column.A correlation basedon the relative molecular mass of the proteins and the packing porosity was developed and used topredict the effective diffusion coefficient of a protein in the Porous packing.The predicted valuesof effective diffusion coefficient were very consistent with the experimental results with the averageerror of 8.6%.     

基团贡献法估算氯代化合物正辛醇-水分配系数

A novel method named two-level group contribution （GC-K） method for the estimation of octanol-water partition coefficient （Kow） of chloride hydrocarbon is presented. The equation includes only normal boiling points and molecular weight of compounds. Group contribution parameters of 12 first-level groups and 7 second-level groups for Kow are obtained by correlating experimental data of three types including 57 compounds. By comparing the estimation results of the first-level with that of the two-level groups, it was observed that the latter is better with the addition of the modification of proximity effects. When compared with Marrero＇s three-level group contribution approach and atom-fragment contribution method （AFC）, the accuracy of the average relative error of GC-K by first-level groups is 7.20% and is preferred to other methods.