Lumped- Differential Formulations for Drying in Capillary Porous Media

Simultaneous heat and mass transfer, during drying of moist capillary porous media, is modeled through different lumped-differential formulations, obtained from spatial integration of the original set of Luikov's equations for temperature and moisture potential. Besides the classical lumped system analysis, improved formulations are proposed, of same mathematicai simplicity, based on approximate evaluations of both temperature and moisture gradients within the medium. The relative merits of such improved zero-dimensional formulations are established, through critical comparisons against analytical solutions for the full partial diflerential system, over a wide range of the governing parameters.     

Lumped- Differential Formulations for Drying in Capillary Porous Media

ABSTRACT

Simultaneous heat and mass transfer, during drying of moist capillary porous media, is modeled through different lumped-differential formulations, obtained from spatial integration of the original set of Luikov's equations for temperature and moisture potential. Besides the classical lumped system analysis, improved formulations are proposed, of same mathematicai simplicity, based on approximate evaluations of both temperature and moisture gradients within the medium. The relative merits of such improved zero-dimensional formulations are established, through critical comparisons against analytical solutions for the full partial diflerential system, over a wide range of the governing parameters.     

Analysis and Application OF Luikov's Heat,Mass, and Pressure Transfer Model to a Capillary Porous Media

ABSTRACT

Luikov's system of partial differential equations for heat, mass and pressure transfer war applied to describe the drying process in a capillary porous body. A two dimensional finite element model were formulated to solve the system of equations. The simulated results agreed     

Analysis and Application OF Luikov's Heat, Mass, and Pressure Transfer Model to a Capillary Porous Media

Luikov's system of partial differential equations for heat, mass and pressure transfer war applied to describe the drying process in a capillary porous body. A two dimensional finite element model were formulated to solve the system of equations. The simulated results agreed     

Chemical Vapor Infiltration Rates of ZrO2 into MoSi2 Porous Bodies and Comparison with Model Calculation

Zirconia (ZrO₂) was chemical vapor infiltrated (CVI) into a partially sintered MoSi₂ body (preform) by using zirconium n -propoxide (Zr(OC₃H₇)₄) as a gas precursor. Infiltration distances at different conditions were compared with the calculated results. Chemical vapor deposition (CVD) film growth rates of ZrO₂ were measured, and the data were incorporated into the model calculations. Two models were used to analyze the observed infiltration distances. Initially a conventional model assuming a pore with constant radius (SP model) was used. With this model, it was possible to predict the approximate infiltration distance. However, the model cannot predict pore closure and the infiltration distances for a variety of CVI conditions. Secondly, a newly proposed model (PC model) from a previous paper was applied to calculate the infiltration distance. Using this model, it was possible to predict the occurrence of pore closure or the formation of the deposition layer on the preform surface.     

微电子技术对塑料加工业的渗透

综述了国内外电子技术在塑料加工业中的应用现状。主要从注射成型、挤出成型、吹塑成型、计算机辅助设计/制造技术以及微电子技术在着色调控上的应用等方面简述了微处理机的功能和发展动向。本文还对我国90年代微电子技术在塑料加工业中的应用提出了建议和展望。     

Modeling of Matter Extraction from a Capillary Porous Particle with a Bidisperse Capillary Structure

A model is suggested for a particle with a bidisperse capillary structure. A numerical analysis of the model demonstrates that, for the liquid extraction of a desired substance from the particle, there exists an optimum range of oscillation frequencies of the liquid in large pores.     

Stress Measurement Technique to Monitor Porous Silicon Processing

Macroscopic stress measurements are used to monitor Porous Silicon processing. Silicon wafer of 1 cm resistivity, n-type and 1 0 0 orientation were used as starting material. Porous Silicon layers with a porosity of 57% and a thickness of 85 m, fabricated by electrochemical anodisation, were differently dried, then the evolution of the wafer deflection has been followed with storage time in air. Thermal treatments both in inert and oxidant atmosphere have been performed up to 1000°C. The stress behaviour vs. temperature allows to estimate the hydrogen desorption activation energy.     

Factors Affecting the Significance of Gravity on the Infiltration of a Liquid into a Porous Solid

A mathematical model is formulated to illustrate the significance of gravity on the infiltration of a liquid in a porous solid. The result indicates that the relative significance of gravity on the infiltration depth depends on the infiltration time as well as the properties of the permeating liquid and the porous solid. The effect of gravity can be neglected for a short infiltration time, and for infiltration systems with the infiltrating liquid having a large value of surface energy, a small value of wetting angle on the solid, and a low density, and the porous solid having a small equivalent capillary radius and a small tortuosity.     

Flow Kinetics in Porous Ceramics: Understanding with Non-Uniform Capillary Models

The present work describes the development of a two-parameter non-uniform capillary model to describe kinetics of flow in porous solids with complex tortuous varying paths. Experimentally, the rate of fluid flow in such a non-uniform capillary is found to be orders of magnitude slower compared with a corresponding average uniform capillary. This slow rate is explained in terms of an extremely small 'effective' hydrodynamic radius. The origin of such an 'unphysical' radius is rationalized based on geometrical considerations and effective driving forces for flow through a stepped capillary. Infiltration rate parameters are derived from the geometry of the porous medium for both wetting and non-wetting conditions.     

利用钢渣研制多孔陶瓷滤球

本文利用炼钢厂钢渣，添加少量的天然矿物原料制备了气孔率58.21%、平均压碎强度18.94MPa的多孔陶瓷滤球.采用现代测试技术XRD、SEM对多孔陶瓷样品进行了相组成分析及显微结构观察.同时分析了用钢渣制作陶瓷滤球的可行性，展望了它的应用前景。     

Cyclic Infiltration of Porous Zirconia Preforms with a Liquid Solution of Mullite Precursor

Composites of mullite and zirconia were fabricated via the cyclic infiltration of porous zirconia-based preforms with a liquid mullite precursor. The maximal amount of mullite precursor that could be infiltrated was dependent primarily on the initial open porosity of the preforms. When a zirconia preform with an initial open porosity of ∼58% was cyclically infiltrated to saturation, the open porosity was reduced to ∼43%, with a median pore diameter of 15 nm. After sintering at a temperature of 1500°C for 2 h, the saturation-infiltrated zirconia preforms could be densified to ∼98% of the theoretical density. In zirconia samples, infiltrated mullite had a tendency to coalesce into large, elongated grains as the sintering temperature was increased. The presence of infiltrated mullite did not have a significant effect on the zirconia grain structure. The distribution of mullite in the samples was nonuniform, and the distribution profiles varied as the number of infiltration cycles varied. Although the sintered density and hardness showed small improvements after saturation infiltration, the fracture toughness did not increase.     

体积密度可控的多孔陶瓷滤料的研制

本研究以α-Al2O3、硅藻土为主要原料,加入一定量成孔剂、助熔剂,用水做粘结剂制成有一定可塑性的泥料,手工搓球、干燥后经烧成,制备了体积密度可控,性能优异的可用于水处理的多孔陶瓷滤料。采用现代测试方法测定了样品理化性能,观察分析了样品的显微结构,并探讨了影响多孔陶瓷滤料孔特性和体积密度的诸因素。     

Porous PZT Ceramics with Aligned Pore Channels for Energy Harvesting Applications

In this study, aligned porous lead zirconate titanate (PZT) ceramics with high pyroelectric figures‐of‐merit were successfully manufactured by freeze casting using water‐based suspensions. The introduction of aligned pores was demonstrated to have a strong influence on the resultant porous ceramics, in terms of mechanical, dielectric, and pyroelectric properties. As the level of porosity was increased, the relative permittivity decreased, whereas the Curie temperature and dielectric loss increased. The aligned porous structure exhibited improvement in the compressive strength ranging from 19 to 35 MPa, leading to easier handling, better processability and wider applications for such type of porous material. Both types of pyroelectric harvesting figures‐of‐merit (F_E and F′_E) of the PZT ceramics with a porosity level of 25–45 vol% increased in all porous ceramics, for example, from 11.41 to 12.43 pJ/m³/K² and 1.94 to 6.57 pm³/J, respectively, at 25°C, which were shown to be higher than the dense PZT counterpart.     

Synthesis of Porous Ceramics with Complex Pore Structure by Freeze-Dry Processing

Porous ceramics with complex pore structure were synthesized by a freeze-dry process. Freezing-in of a water-based ceramics slurry was done while controlling the growth direction of the ice. Sublimation marks of the ice were generated by drying under reduced pressure. Porous ceramics having a complex pore structure were obtained by sintering the green body: aligned macroscopic open pores contained micropores in their internal walls. The pore structure was substantially affected by the starting slurry concentration and sintering temperature. The pore formation mechanism is discussed in relation to these effects.     

Mesoporous Glass Membranes as Model Systems to Study Gas Diffusion through Porous Media

Porous glass monoliths are suitable model systems to study pore size‐related effects in gas diffusion. Here, mesoporous glass membranes with different surface properties and pore diameters covering the lower mesopore range were synthesized and used to study gas permeation of adsorbable and non‐adsorbable gases. Dynamic single gas permeation measurements were performed using a modified Wicke‐Kallenbach cell. Chemical surface modification of the inner surface of the membranes resulted in altered adsorption and diffusion properties.     

On the Mechanism of Densification of Porous Alumina by Infiltration with an Aqueous Solution of Chromium Oxide

Densification of porous alumina by CrO₃ infiltration was investigated on model composites containing a sapphire interface. Gas–solid deposition of Cr₂O₃ from CrO₃ source on sapphire and glass at 600°C was also investigated. The deposited Cr₂O₃ layers were characterized using X-ray diffraction and transmission electron microscopy. It was found that similar to gas-phase deposition on sapphire, in CrO₃-infiltrated porous alumina Cr₂O₃ grows epitaxially on adjacent alumina surfaces, suggesting a gas–solid condensation mechanism. The deposition rate and morphology of the Cr₂O₃ film deposited on alumina depend strongly on the crystallographic orientation.     

人工快速渗滤处理水中氨氮的实验研究

针对的氮污染问题,采用人工快速渗滤法去除污水中的氨氮。研究了不同的渗滤介质,不同干湿比,不同的氨氮浓度,以及不同的渗滤介质高度对于去除效果的影响。结果表明:在不同干湿比的情况下,去除效果最好的渗滤介质为表层土,其次是煤灰,最后是沙子;其去除效果的好坏相对应的干湿比依次为23∶1、10∶1、4∶1;对于废水的进水浓度,在相同的情况下,进水浓度越高,其去除氨氮的效果越好;渗滤介质越高的渗滤系统去除效果越好。