Application of Pore Size Analyzers in Study of Chinese Angelica Slices Drying

The objective of this article is to study the influence of pore size and distribution in plant tissue on drying behavior of plant materials using Chinese Angelica slices as an example. By using an automatic mercury injection apparatus and automatic surface area–porosity analyzer, the study compares the pore size distribution inside the matrix of a sample dried by 200 W microwave and 60°C hot air. The study also characterizes the matrix microstructure by scanning electronic microscopy (SEM) and discusses the drying dynamics of the sample, as well as the rehydration property of the dried sample. This work may be helpful for further investigation of the optimization of drying technology focused on micromechanisms and the quality of dried products.     

干污泥表面形貌及孔隙分布规律

污泥干燥焚烧以回收其热能的资源化利用正受到越来越多的关注。污泥干燥过程中,孔隙的大小及其分布直接影响污泥中液体及气体的传递过程．进而影响干燥速率。为研究干污泥表面形貌及孔隙分布规律,采用扫描电子显微镜观测了干污泥表面形貌。利用动态氮吸附法测量了干污泥的孔隙大小。利用数理统计方法研究了孔隙分布规律,研究结果表明干污泥的孔隙分布服从对数正态分布。建立了孔隙分布模型,求解了5种干污泥的孔隙分布特征参数,模型计算值与实际测量值吻合较好,均方根误差小于18．2％,所建立的干污泥孔隙分布模型具有一定的通用性及准确性。     

Effect of Attapulgite Pore Size Distribution on Soybean Oil Bleaching

The pore size distribution and specific surface area of the attapulgite was a crucial parameter for the uptake of pigments of oil. Bleaching of the soybean oil with three attapulgites with different pore size distribution, which were assigned a, b, and c, respectively was investigated. The specific surface area and the pore size distribution of the attapulgites were characterized. The Freundlich isotherm analysis was used to evaluate the sorption capacity of the three attapulgite. Sample b gave the highest surface area and sample c the lowest. Sample b exhibited a wider pore distribution (8–65 Å) whereas samples a and c had more micropores smaller than 15 Å. Sample a, in contrast to samples b and c, was characterized by some larger pores (100–170 Å). The sorption capacity followed the sequence: attapulgite sample c > attapulgite sample a > attapulgite sample b. The sorption capacity was decided by the pore size distribution. The more pores with a distribution range 8–32 Å (i.e., close to the diameter of the pigments), the more pigments removed. The attapulgite sample c, which had most pores (8–32 Å) was the best.     

多孔介质干燥孔道网络模型的研究进展

建立在物质微观传输基础上的孔道网络干燥理论，通过完全离散化的方法在孔道等级上对干燥过程进行研究，描述了多孔介质内部结构参数对干燥过程的影响。介绍了建立孔道网络模型的原理和方法，阐述了基于单元体上孔道网络研究的内容及目的，综述了基于产品等级上孔道网络研究的最新进展，阐明了孔道网络模型方法对干燥理论研究的重要意义。指出，进一步提高网络模型中孔道的拓扑等价性、形状的不规则性及尺寸的相关性，探索网络构建新方法以及增加孔道网络信息量，是孔道网络干燥理论的主要发展方向，并应加强同分形、渗流理论的进一步结合。     

Effect of Calcination Conditions on Crystalline Structure and Pore Size Distribution for a Mesoporous Alumina

In this article, a mesoporous commercial alumina was calcined in the temperature range of 600°C–1200°C. The effect of several parameters such as calcination temperature, calcination time, heating rate, and calcination steps on phase transformation and crystal size was experimentally investigated. The characterization of the commercial mesoporous alumina and samples calcined at 1000°C, 1040°C, 1070°C, 1100°C, and 1200°C by single-step and multi-step calcination was performed using XRD and N₂ adsorption/desorption techniques. For the commercial mesoporous alumina, TG/DTA analysis was also performed. Experimental results showed that mostly pure α-Al₂O₃ was obtained at 1100°C.     

Isothermal Drying of Pore Networks: Influence of Friction for Different Pore Structures

An existing network model for isothermal drying of capillary porous media is extended to account for viscosity in the liquid phase so that it is no longer restricted to structures with large pores. Modeling challenges and solution methods are presented in detail. The model is compared with a bundle of capillaries model of drying. Finally, simulation results for two-dimensional pore networks with mono-modal and bimodal pore structure are shown and discussed.     

Isothermal Drying of Pore Networks: Influence of Friction for Different Pore Structures

An existing network model for isothermal drying of capillary porous media is extended to account for viscosity in the liquid phase so that it is no longer restricted to structures with large pores. Modeling challenges and solution methods are presented in detail. The model is compared with a bundle of capillaries model of drying. Finally, simulation results for two-dimensional pore networks with mono-modal and bimodal pore structure are shown and discussed.     

炭分子筛的孔径分布研究

采用容积法测定了CO2在两种炭分子筛（CMS-200A、CMS-200B）上的吸附等温线,温度为273K、相对压力为0.000001～0.9。通过HK模型和D-R方程对吸附平衡数据进行分析,计算得到了两种炭分子筛的孔径分布。结果表明：两者的孔径分布主要在0.35～0.8nm之间,CMS-200B的平均孔径略大于CMS-200A。HK模型和D-R方程两种方法均可以反映出两种炭分子筛孔径分布的差异,且计算得到的结论是一致的。     

Effect of Pore Size and Particle Size Distribution on Granular Bed Filtration and Microfiltration

Abstract

The paper reviews the effect of particle size distribution and pore size distribution on granular bed filter and crossflow microfiltration performance. The experimental results of the granular bed filter with pollen particles in suspension showed that the presence of large particles improved the filter efficiency of smaller particles in suspension. Microfiltration results with bi and tri‐modal latex suspensions showed that the permeate flux and the quality were significantly affected by the particle size and its distribution, especially when the particle size was smaller than the pore size of the membrane. The mathematical model simulation results of granular bed filtration show that media pore size distribution is an important parameter of filtration for the particle removal and pressure drop across the filter.     

多孔陶瓷孔径及其分布测定方法研究进展

孔径及其分布决定了多孔陶瓷的性能及应用,因此对其测定和定量表征非常重要。本文综述了多孔陶瓷孔径及孔径分布的常见测定方法,包括气泡法、压汞法、气体透过法、气体吸附法、气体渗透法、液-液法、悬浮液过滤法、X射线小角度散射法、核磁共振成像法、X射线断层扫描法以及电子显微镜图像分析法。比较了各种测试方法的优缺点,认为电子显微镜图像分析法是最直接有效的测定方法,并对多孔陶瓷的测试表征方法提出了展望。     

Pore-Level Modeling of Isothermal Drying of Pore Networks Accounting for Evaporation,Viscous Flow,and Shrinking

Abstract

Simulation results of pore-level drying of non-hygroscopic, non-rigid, liquid-wet porous media are presented. Two- and three-dimensional pore networks represent pore spaces. Two kinds of mechanisms are considered: evaporation and hydraulic flow. The process is considered under isothermal conditions. Capillary forces thus dominate over viscous forces and the drying is considered as a modified form of invasion percolation. Liquid in pore corners allows for hydraulic connection throughout the network. During drying, liquid is replaced by vapor by two fundamental mechanisms: evaporation and pressure gradient–driven liquid flow. The development of capillary pressure as menisci turn concave induces shrinkage of the matrix, which contributes to the pressure gradient that drives liquid toward the surface of the network. Using Monte Carlo simulation, we find evaporation and drainage times; the shortest calculated indicates the controlling mechanism. Here we report distributions of liquid and vapor as drying time advances. For the calculation of transport properties, details of pore space and displacement are subsumed in pore conductances. Solving for the pressure field in each phase, vapor and liquid, we find a single effective conductance for each phase as a function of liquid saturation. Along with the effective conductance for the liquid-saturated network, the relative permeability of liquid and diffusivity of vapor are calculated.     

Pore-Level Modeling of Isothermal Drying of Pore Networks Accounting for Evaporation, Viscous Flow, and Shrinking

Simulation results of pore-level drying of non-hygroscopic, non-rigid, liquid-wet porous media are presented. Two- and three-dimensional pore networks represent pore spaces. Two kinds of mechanisms are considered: evaporation and hydraulic flow. The process is considered under isothermal conditions. Capillary forces thus dominate over viscous forces and the drying is considered as a modified form of invasion percolation. Liquid in pore corners allows for hydraulic connection throughout the network. During drying, liquid is replaced by vapor by two fundamental mechanisms: evaporation and pressure gradient-driven liquid flow. The development of capillary pressure as menisci turn concave induces shrinkage of the matrix, which contributes to the pressure gradient that drives liquid toward the surface of the network. Using Monte Carlo simulation, we find evaporation and drainage times; the shortest calculated indicates the controlling mechanism. Here we report distributions of liquid and vapor as drying time advances. For the calculation of transport properties, details of pore space and displacement are subsumed in pore conductances. Solving for the pressure field in each phase, vapor and liquid, we find a single effective conductance for each phase as a function of liquid saturation. Along with the effective conductance for the liquid-saturated network, the relative permeability of liquid and diffusivity of vapor are calculated.     

聚醚砜中空纤维血浆分离膜的孔径大小及分布

本文采用场致扫描电镜的显微观察法和膜对溶质的粒子筛分法测定聚醚砜中空纤维血浆分离膜的孔径大小及分布。通过显微镜观察统计得到膜的几何平均孔径为229nm,膜孔孔径分布在150nm,-350nm,筛分法测试得到膜的平均孔径为197nm。平均孔径大小约为200nm的聚醚砜中空纤维膜适合做血浆分离膜。     

Modeling of the Relationship Between Pore Size Distribution and Thickness of Ceramic MF Membrane

The pore size distribution(PSD)measured by the gas bubble point(GBP)method ofceramic microfiltration(MF)membranes prepared by suspension technique was found to be signifi-cantly influenced by the membrane thickness.A culm-like model for pore structure was introduced tocharacterize the membrane pores instead of the conventional model which does not reflect the radiusvariation along the pore passages and is unable to explain the thickness effect on the membrane PSD.A laminate structure,taking the culm-like model for pore structure into consideration,was hypoth-esized for ceramic MF membranes.A mathematical model was then established to quantitativelydescribe the relationship between the membrane number PSD and the membrane thickness.Goodresults were obtained for the correlation of mean pore size and simulation of the PSD for ceramicMF membranes.     

玻璃基TiO_2膜的孔径尺寸对其光催化性能的影响

通过在溶胶—凝胶溶液中加入聚乙烯乙二醇有机聚合物 ,利用平板玻璃作衬底 ,制备了多孔 Ti O2 薄膜。扫描电镜观察表明 ,一定的热处理条件下 ,有机聚合物可以显著地改变 Ti O2 薄膜的孔径尺寸。光催化结果显示 :当 Ti O2 膜的孔径尺寸在 15 0～ 2 5 0 nm时 ,它的光催化性能较好。     

几种椰壳活性炭材料的孔结构分析

为了筛选在异丙苯法生产苯酚工艺中吸附分离α-甲基苯乙烯的吸附剂，测定了4种椰壳活性炭材料的氮吸附等温线，并用BET模型、t图法、BJH理论等方法对孔结构进行分析与表征。结果表明：2号活性炭为微孔型，具有大量2．3nm以下的孔隙。1号、3号、4号活性炭除了微孔外还含有一定量的中孔。4号活性炭中孔率超过50％，拥有最小的平均中孔孔径，对α-甲基苯乙烯有较强的吸附能力，较适合作为异丙苯法生产苯酚工艺中α-甲基苯乙烯的吸附剂。     

氧化铝微滤膜孔径的影响因素及控制

首次发现膜泡压孔径随膜厚增加而减小;随烧结温度升高,膜孔道实际几何孔径基本上不变,泡压孔径增大;膜孔径的控制方法为：根据孔径要求选择适当的微粉,通过控制膜厚准确控制膜孔径。