对改进液相扩散膜池法的初步考察

针对膜池法的主要缺点,考察选用了金属扩散膜代替传统的玻璃膜,以缩短测定时间,使膜池法更便于应用。根据考察,所选平均透孔半径为1。42μ,厚100μ的多孔金属烧结膜可用于膜池法测定液相扩散系数。所测水-乙醇和乙醇-四氯化碳物系在25.00℃的扩散系数与文献值基本一致。所需测定时间由传统玻璃膜扩散池的2～4天减少到1.5～4小时。利用改进的膜池法测定了25.00℃的苯-四氯化碳物系在全浓度范围内和正丙醇-四氯化碳物系在部分浓度下的扩散系数。实验所测扩散系数的相对误差小于1.8％。     

膜池法测定维生素B2在水中的扩散系数

本文用具有金属膜的膜池测定了稀溶液中维生素Ｂ２在水中的扩散系数，同时也考察了温度对该扩散系数的影响。实验结果表明：用金属膜替代玻璃膜使传统膜池法测定扩散系数的时间大为缩短（仅为原来的１／３０），且所测结果真实可靠     

纯溶剂在线性低密度聚乙烯膜中的渗透汽化

用渗透汽化实验装置测定了5种常用化工溶剂在线性低密度聚乙烯材料中的渗透性能,考察不同温度对于5种溶剂的渗透通量的影响。通过渗透通量与温度的Arrhenius关系,回归拟合得到各种溶剂的渗透活化能;并采用吸附溶胀实验测定了5种纯溶剂在该膜材料中的平衡吸附量,以此推算出25℃条件下5种溶剂在膜材料内部的扩散系数。结果表明,5种溶剂的渗透通量的顺序为正己烷正庚烷环己烷丙酮甲基吡咯烷酮,吸附量大小顺序为甲基吡咯烷酮环己烷正己烷正庚烷丙酮。     

GB 18581—2009标准中苯系物测定方法的改进和准确度的提高

在GB 18581—2009标准中规定的苯系物测定方法的基础上,提出了苯系物测定的改进方法。采用气相色谱法测定了一系列浓度的正庚烷的峰面积,由此即可得出一定范围内任何质量的正庚烷所对应的峰面积,经计算可得出各校准物的校正因子及含量。新方法得到的结果与GB 18581—2009标准中规定的方法进行了比对,表明新方法不仅简化了实验,也提高了苯系物测定的准确度,提高了实验效率。     

数字全息法测量液相扩散系数实验研究

采用数字全息干涉法测量了25℃乙二醇-水物系的扩散系数。详细介绍了实验方法以及2种处理干涉图像获得扩散系数的方法,即横条纹法和弯条纹法。通过测量25℃时0.33 mol/L KCl溶液的扩散验证了实验的精确性。分别用2种方法获得了6个不同质量分数下的乙二醇-水物系的扩散系数,并与文献值进行了对比。结果表明,弯曲条纹法的平均相对偏差是1.3%,比水平条纹法的1.7%小,同时,弯曲条纹法的平均标准偏差更小,说明波动更小。     

碳酸二乙酯在正庚烷和空气中质扩散系数测量

利用自行搭建的数字激光全息干涉法测量流体液液、气液质扩散系数的实验装置,在标准大气压下,温度在278.15—338.15 K内,测量了含氧替代燃料碳酸二乙酯分别在正庚烷和空气中21个温度点的质扩散系数;同时,使用Wilke-chang方程、Scheibel方程和Reddy-Doraiswamy方程对碳酸二乙酯在正庚烷中的质扩散系数进行了估算,并与实验数据进行了比较分析。为替代燃料碳酸二乙酯的科研开发提供了热物性基础数据。     

正庚烷在5A分子筛上的高温吸附/脱附及扩散性能

用智能重量分析仪(IGA-100)在较高温度下测定了5A分子筛(自制)对正庚烷吸附/脱附等温线及其滞后环;计算TIE庚烷在5A分子筛上的吸附热和吸附、脱附扩散系数,分析了正庚烷在5A分子筛微孔内吸附作用.结果表明:吸附温度升高,正庚烷吸附等温线优惠程度明显降低,有吸附滞后环;在523 K下,5A对正庚烷的平衡吸附量为0...     

组合导向浮阀塔板的板效率研究

在直径为0.75 m的不锈钢塔内,以正庚烷-环己烷为物系,常压全回流条件下,进行了组合导向浮阀传质效率的研究,测试了该塔板的气、液相默弗里板效率和全塔效率,并和F1型浮阀塔板的全塔效率进行了对比。采用AIChE与Chen,Chuang 2种传质模型计算了组合导向浮阀塔板的点效率值。研究了AIChE与Molnar 2种计算涡流扩散系数的方法对默弗里板效率的影响。实验结果表明:在正常操作范围内组合导向浮阀塔板全塔效率高于F1型浮阀塔板。经比较实验值与模型值,发现采用Chen,Chuang预测点效率和Molnar方法计算涡流扩散系数所估计的默弗里板效率偏差在11%内。     

萃取精馏法分离乙酸乙酯-正庚烷的研究

通过萃取精馏法,以N-甲基吡咯烷酮(NMP)为萃取剂分离乙酸乙酯-正庚烷的共沸物系。利用溶剂选择原理和UNIFAC基团贡献法筛选N-甲基吡咯烷酮作为萃取精馏的萃取剂,同时通过常压下乙酸乙酯-正庚烷体系和加入萃取剂N-甲基吡咯烷酮后的气液平衡实验,证明N-甲基吡咯烷酮能够打破共沸。并进行间歇萃取精馏实验,填料塔理论塔板数为35,回流比1.0,可以得到质量分数为98.3%的正庚烷,回收率为73.4%。最后在Aspen Plus软件帮助下研究N-甲基吡咯烷酮连续萃取精馏分离乙酸乙酯-正庚烷物系的工艺流程,萃取精馏塔塔顶正庚烷的质量分数可达99.5%,溶剂回收塔塔底回收纯N-甲基吡咯烷酮套用,为进一步的工业应用提供依据。     

甲苯-正庚烷-环丁砜、环丁砜-正庚烷-水——三元体系液液平衡数据的测定与热力学关联

本文测定了甲苯-正庚烷-环丁砜三元体系在30℃和50℃下的液液分层曲线和结线数据,采用了以液液分层曲线和体系物性相结合的分析方法,获得了可靠的数据.本文还测定了环丁砜—正庚烷-水三元体系在50℃下的液液分层曲线,作出了结线.对前一休系的数据进行了热力学关联,求出30℃及50℃时UNIQUAC方程参数.对两个体系均用UNIFAC方法进行预测.计算所得结果相当满意.     

Thermodynamics and mass transfer kinetics of phenol in reversed phase liquid chromatography

The thermodynamics and the mass transfer kinetics of the chromatographic system made of phenol, in a water-acetonitrile mobile phase, on a C18 RPLC column, were studied in the temperature range from 21 to and the interstitial velocity range of 0.021 to 1.27 cm/s. The equilibrium isotherm was accurately approximated by a multilayer model assuming lateral interactions between adsorbed molecules. The parameters of the kinetics of the phenol mass transfer in this column were measured by the method of moments. These data were analyzed using the available models and correlations. It was proven that the parameters of the mass transfer kinetics measured under linear conditions could be successfully used for the prediction of the concentration profiles obtained under overloaded conditions.     

Measurement of intraparticle diffusion in reversed phase liquid chromatography

The intraparticle diffusion coefficient was measured using a method based on the fitting of a set of experimental chromatographic profiles to the lumped pore diffusion model. For this purpose, both the analytical solution of the model in the Laplace domain and a numerical method were used. There was an excellent agreement between the results given by the two methods. These results are compared to those obtained by moment analysis of the same set of chromatographic profiles and by the determination of the intraparticle diffusion coefficient from the second central moment of these bands. Nearly identical results were obtained with these two independent methods. The values of the intraparticle diffusion coefficient, D_e, for rubrene in pure methanol was found to be by the modeling method and by the moment analysis method. These values increase with increasing water concentration, to 1.10×10⁻⁶ and , respectively, in a methanol/water solution and to 1.63×10⁻⁶ and , respectively, in a solution.These results confirm the validity and the consistency of the lumped pore model and the moment analysis theory. They show that both approaches describe correctly the mass transfer kinetics in the particles of packing material during the chromatographic process. Systematic determinations of the intraparticle diffusion coefficient can now be undertaken and the influence of various experimental parameters on this important property of packing materials can be investigated.     

Moisture Diffusivity in Food and Biological Materials

The spatial distributions of water content and temperature inside moist food or biological materials (native or manufactured) during drying are important in interpretation and prediction of quality changes. The dynamics of drying in modern devices is not simple—for instance, the process of intermittent drying—thus, a liquid diffusion model is expected to be the simplest and hopefully the very effective. In this article, some controversial aspects of the concept of the effective Fickian liquid moisture diffusivity are described and discussed. These discussions are intended to stimulate more interest in working toward a better rationalization of the liquid diffusion concept. It is suggested that such a parameter may even be called a “liquid depletion coefficient” instead to avoid confusion at the fundamental level. An improved alternative model from the effective liquid diffusion model is possible and some new ideas have been explored.     

Effect of grain boundary diffusion on electrolyte stability in direct carbon fuel cells with antimony anodes

Direct carbon fuel cells (DCFC) that employ solid oxide electrolytes and molten Sb anodes are promising for the efficient generation of electricity using a range of carbonaceous fuels. The present study examined the etching of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) electrolytes by Sb₂O₃ produced during fuel-cell operation. Migration of Sb along grain boundaries and electrolyte corrosion were observed for both polycrystalline YSZ and GDC electrolytes; however, corrosion and electrolyte thinning were not observed for a single-crystal YSZ electrolyte, even after long-term operation. These results indicate that Sb migration along grain boundaries plays a significant role in electrolyte corrosion in DCFCs with molten Sb anodes. Several strategies for avoiding this problem are also discussed.     

Moisture Diffusivity in Food and Biological Materials

The spatial distributions of water content and temperature inside moist food or biological materials (native or manufactured) during drying are important in interpretation and prediction of quality changes. The dynamics of drying in modern devices is not simple—for instance, the process of intermittent drying—thus, a liquid diffusion model is expected to be the simplest and hopefully the very effective. In this article, some controversial aspects of the concept of the effective Fickian liquid moisture diffusivity are described and discussed. These discussions are intended to stimulate more interest in working toward a better rationalization of the liquid diffusion concept. It is suggested that such a parameter may even be called a “liquid depletion coefficient” instead to avoid confusion at the fundamental level. An improved alternative model from the effective liquid diffusion model is possible and some new ideas have been explored.     

Experimental validation of physico-chemical models of effective diffusion in chromatographic columns packed with superficially porous particles

The effective diffusion coefficient of a non-retained compound (uracil) was measured with the peak parking (PP) method for two series (4.6 mm×100 mm and 2.1 mm×100 mm) of six replicate columns packed with the same batch of superficially porous Kinetex-C₁₈ particles. The abilities of four different models of effective diffusion in packed beds to account for the experimental data are compared. These models include the conventional Knox time-averaged model, the extension to molecular diffusion of the Landauer electrical conductance model, the Garnett diffusion model for the inclusion of core-shell spheres down to infinitesimal small sizes, and the stochastic Torquato model for a random dispersion of spheres in contact.The choice of a non-retained compound for this purpose is justified by the facts that the diffusivity of this compound through the porous shell can be estimated independently from its internal porosity derived from inverse size-exclusion chromatography (ISEC) data, that the internal obstruction factor can be assessed by nuclear magnetic resonance (NMR) using the spin-echo pulsed field-gradient method, and that the hindrance diffusion factor can be estimated with either the Renkin or the Brenner correlations. The experimental effective diffusion coefficient of uracil was found to be in excellent agreement with the value predicted by Knox semi-empirical model, in good agreement with those predicted by Torquato and Landauer models while the Garnett model failed definitely. In conclusion, the longitudinal diffusion terms of columns packed with core-shell particles cannot yet be accurately predicted by any of the sophisticated, physically relevant models of effective diffusion actually available in the scientific literature.     

含SiO2添加剂促进CaZrO3分解机理研究

骨料部分采用60%的锆酸钙颗粒(粒度≤0.374mm和≤0.147mm),基质部分采用30%的α-Al2O3微粉和10%的含SiO2添加剂(分别为硅灰石、熔融石英、锆英石及其复合物),成型、干燥后于1550℃3h烧成,然后对烧后试样进行了扫描电镜、XRD分析,并借助相图对CaZrO3的分解机理从热力学与动力学上进行了研究。研究结果表明:含SiO2添加剂都能促进CaZrO3的分解,其扩散传质速度直接决定着CaZrO3的分解程度,硅灰石(CaSiO3)及其复合添加剂由于在与CaZrO3的反应中生成较大量的液相而使其传质速度加快,从而使CaZrO3分解的程度变大,其中以CaSiO3-SiO2复合添加剂的促进CaZrO3分解程度最大。     

Influence of liquid properties on flow regime and backmixing in a special bubble column

An experiment aimed to link the extent of axial mixing in a special configuration bubble column reactor with different liquid properties (water, 10% K₂CO₃ solution, 20% K₂CO₃ solution, paraffine). The experimental results proved that, increase of liquid viscosity will delay the mean residence time and weaken gas axial backmixing. Increased surface tension leads to lower flow regime transition point and higher overall gas holdup. Surface tension is the dominant factor to influence of gas axial backmixing degree. A simple RTD model for homogeneous–heterogeneous regime is developed in the column of 0.1 m diameter and the corresponding correlation of gas axial dispersion coefficients is . The model is verified by experiments with air/water/paraffine system. Good agreement is found. As a byproduct, a non-empirical formula for gas holdup results, _g/(1−_g)⁴ = 0.579 (u_gμ/σ)^0.918 (μ⁴g/ρ_Lσ³)^−0.252. But both correlations cannot be available for K₂CO₃ solution with addition of small quantities of surface tension in pure liquid.     

Pore-network modeling of liquid water transport in gas diffusion layer of a polymer electrolyte fuel cell

A pore-network model is developed to study the liquid water movement and flooding in a gas diffusion layer (GDL), with the GDL morphology taken into account. The dynamics of liquid water transport at the pore-scale and evolution of saturation profile in a GDL under realistic fuel cell operating conditions is examined for the first time. It is found that capillary forces control liquid water transport in the GDL and that liquid water moves in connected clusters with finger-like liquid waterfronts, rendering concave-shaped saturation profiles characteristic of fractal capillary fingering. The effect of liquid coverage at the GDL–channel interface on the liquid water transport inside GDL is also studied, and it is found that liquid coverage at the GDL–channel interface results in pressure buildup inside the GDL causing the liquid water to break out from preferential locations.     

Investigation of liquid water in gas diffusion layers of polymer electrolyte fuel cells using X-ray tomographic microscopy

In polymer electrolyte fuel cells (PEFCs), condensation of water within the pore network of the gas diffusion layers (GDL) can influence the gas transport properties and thus reduce the electrochemical conversion rates. The use of X-ray tomographic microscopy (XTM), which allows for a resolution in the order of one micrometer is investigated for studying ex situ the local saturation in GDL's. The strength of XTM is the high spatial resolution with simultaneous contrast for water and carbon, allowing for non-destructive 3D-imaging of the solid and the contained water. The application of this method for imaging the ex situ water intrusion into the porous network of GDLs is explored using absorption and phase contrast methods. It is shown that the inhomogeneous filling behavior of GDL materials can indeed be visualized with sufficient resolution. For Toray paper TGP-H-060 the local saturation was measured as function of the water pressure. The results, evaluated in 1D, 2D and 3D show a liquid water retention effect at the denser layers near the surface. A comparison with established capillary pressure functions is presented. Altogether, the results show the potential of the XTM-method as a tool for studying the liquid water behavior in PEFC on a microscopic scale.