考虑多孔介质渗透率变化的宾汉流体渗透注浆扩散模型

渗透注浆是一种广泛应用于岩土多孔介质加固的方法,但已有基于浆液流变方程和平衡方程的研究,侧重分析浆液本身性质如黏度时变性、滤过效应、自身重力等对渗透注浆扩散范围的影响,尚未考虑浆液在孔隙内的流动阻力对多孔介质渗透率的影响,导致现有理论解析结果与试验测试结果相差较大。因此,基于黏性流体的运动方程、连续方程和平衡方程,引入浆液在孔隙内的流动阻力对多孔介质渗透率的影响,推导获得多孔介质渗透率随介质孔隙特性、注浆施工参数和注浆扩散半径的函数解析表达式,据此建立考虑多孔介质渗透率变化的浆液扩散控制方程。与已有理论结果对比表明,考虑浆液流动阻力影响的理论结果更接近试验结果,可以验证该理论方法的有效性。参数分析结果表明:考虑浆液在孔隙内的流动阻力时,岩土多孔介质渗透率随注浆时间的增加呈现先迅速降低后缓慢上升趋势,随注浆压力的增大呈现逐渐下降趋势;对于工程中常见的符合宾汉流体性质的水泥浆液材料,当注浆时间小于5 min时,多孔介质渗透率变化是影响浆液扩散的主控因素,超过7 min后,浆液黏度时变性成为主控因素。研究成果能为岩土多孔介质渗透注浆工程实际中注浆参数选取和质量控制起到良好的理论指导意义。

高孔洞率多孔砖的研制

研制生产了20孔、21孔和24孔3种孔型的多孔砖 ,使孔洞率由原有的22 %逐步提高到33.4%。介绍了工艺流程、主要工艺参数、产品性能 ;在进行经济分析后指出 ,生产高孔洞率多孔砖 ,虽然成本有所提高 ,但是节约土地资源 ,节省燃煤、燃油 ,减少大气污染 。

幂律流体在多孔介质中径向渗流的分形模型

基于分形理论及毛细管模型,本文研究了非牛顿幂律流体在各向同性多孔介质中径向流动问题,推导了幂律流体径向有效渗透率的分形解析表达式.研究结果表明,幂律流体径向有效无量纲渗透率模型和Chang and Yortsos’s模型吻合很好;同时还得出幂律流体径向有效渗透率随孔隙率、幂指数的增加而增加,随迂曲度分形维数的增加而减少.

粗集料级配对多孔混凝土性能的影响研究

采用连续级配粗集料和单一粒级粗集料配制多孔混凝土,研究了集料级配对多孔混凝土的表观密度﹑抗压强度﹑空隙率﹑透水系数的影响。试验结果表明,在相同集灰比情况下,采用单一粒级的粗集料配制的多孔混凝土能获得较高的空隙率(大于22%),且抗压强度达15MPa,可满足对护坡工程所用生态混凝土提出的要求。

多孔硅结构电镜图像的数字处理

多孔硅在光电子和传感器领域是一种具有重要应用价值的材料,多孔硅网络结构的形状纹理直接影响其光学和热学性能。运用数字图像处理分析方法对多孔硅结构电子显微镜图像(SEM)进行特征提取,为多孔化率的测定提供了重要依据。

响应面法优化火龙果真空冷冻干燥工艺

目的:提高火龙果冻干品酥脆度。方法:以美龙1号红肉火龙果为研究对象,通过pearson分析选出与感官评价相关性最高的多孔率为检测指标,考察切片厚度、预冻时间、干燥气压和干燥时间对火龙果冻干品品质的影响,并采用Box-Behnken响应面分析法优化火龙果真空冷冻干燥工艺。结果:切片厚度、预冻时间和干燥时间与火龙果冻干品的多孔率线性相关显著;最佳工艺条件为切片厚度7 mm、预冻时间30 h、干燥气压43 Pa、干燥时间40 h,此工艺生产的火龙果冻干品多孔率最高、表面平整、口感酥脆、颜色均匀鲜艳。结论:利用响应面法改进切片厚度、预冻时间、干燥气压和干燥时间工艺参数可以提高火龙果冻干品品质。

微孔硅酸钙干燥相关物理量的研究

介绍了一些干燥相关物理量的研究方法，并对微孔硅酸钙的干燥相关物理量进行了初步的研究．根据电子扫描电镜的成象分析，获得了该种材料内部结构的固有规律，并在此基础上通过理论分析和一些简单的实验相结合的方法，得到了诸如微孔硅酸钙的多孔率、毛细压力和解吸等温线等物理量，为进一步深入研究微孔硅酸钙的干燥特性提供了依据．

Pore structure and liquid flow velocity distribution in water-saturated porous media probed by MRI

Magnetic resonance imaging （MRI） was used to probe the structure and flow velocity within the interparticle space of a packed bed of agar beads under water-saturated condition. The images of the velocity field at three different flow rates were obtained. To determine the pore-parameter of the porous media, the internal structure of the bed was also obtained using image processing technique. The results show that the porosity of the sample is 31.28% and the fitting curve for the distribution of pore equivalent diameter follows Gaussian distribution. The velocity profiles do shift as the flow rate varies and the solution flow through the void space is not a homogeneous flow in any pores. The velocity distributions within the pore are roughly parabolic with the local maximum being near the center. About half of the velocity components are in the class of 0-1 cm/s. The frequency of lower velocity components is lower at higher flow rate, but to higher velocity components, it is just the opposite.

Open-celled porous NiAl intermetallics prepared by replication of carbamide space-holders

Open-celled porous NiAl intermetallics with adjustable pore characteristics and mechanical properties were successfully prepared by using spherical carbamide as space-holders via combustion synthesis.Examinations of macroscopic and microscopic morphologies as well as the quasi-static compressive test for the resultant materials were carried out.Depending on the volume fraction and particle size of the carbamide,the porosity and pore size of the porous NiAl intermetallics can be controlled freely in a range of 57.57%-84.58% and 0.4-2.0 mm,respectively.Furthermore,quasi-static compressive tests indicate that the mechanical behavior of the present porous materials is in good agreement with the Gibson-Ashby model.

Sintering preparation of porous sound-absorbing materials from steel slag

Porous sound-absorbing materials were prepared from steel slag using waste expanded polystyrene（EPS） particles as pore former.The influences of the experimental conditions such as fly ash content,sintering temperature,sintering time,and pore former addition on the performance of the porous sound-absorbing materials were investigated.The results show that the porosity of the specimens can reach above 50.0%;the compressive strength and average sound-adsorption coefficient of the sintered specimens are above 3.0 MPa and 0.47,respectively.The optimum preparation conditions for the steel slag porous sound-absorbing materials are as follows：mass fraction of fly ash 50%,waste EPS particles 3.6 g,sintering temperature 1100℃,and sintering time 7.5h,which are determined by considering the properties of the sound-absorbing materials,energy consumption and cost.

Pore structure of unidirectional solidified lotus-type porous silicon

Lotus-type porous silicon with elongated pores was fabricated by unidirectional solidification under pressurized hydrogen. Porosity, pore diameter, and pore length can be adjusted by changing solidification speed and hydrogen pressure. The porosity of the ingot is nearly constant under different solidification speeds, but decreases with the increase of hydrogen pressure. The overall porosities of ingots fabricated at different hydrogen pressures were evaluated through a theoretical model. Findings are in good agreement with experimental values. The average pore diameter and pore length increase simultaneously while the average pore aspect ratio changes slightly with the decreases of solidification speed and hydrogen pressure. The average pore length is raised from 7 to 24 mm and the pore aspect ratio is raised from 8 to 20 respectively with the average pore diameter promoted by about 0.3 mm through improving the superheat degree of the melt from 200 to 300 K.

Fabrication and flexural strength of porous Si3N4 ceramics with Li2CO3 and Y2O3 as sintering additives

By employing sintering additives of Li2CO3 and Y2O3,porous Si3N4 ceramics are prepared after experiencing the processes of sintering and post-vacuum heat treatment at 1680 and 1550°C,respectively.The experimental results demonstrate the completed phase transformation fromαtoβ-Si3N4 in Si3N4 ceramic samples with a amount of 1.60 wt%Li2CO3(0.65 wt%Li2O)and 0.33 wt%Y2O3 additives.The as-synthesized porous Si3N4 ceramics exhibit high flexural strength((126.7±2.7)MPa)and high open porosity of 50.4%at elevated temperature(1200°C).These results are attributed to the significant role of added Li2CO3 as sintering additive,where the volatilization of intergranular glassy phase occurs during sintering process.Therefore,porous Si3N4 ceramics with desired mechanical property prepared by altering the addition of sintering additives demonstrate their great potential as a promising candidate for high temperature applications.

Preparation and oxygen permeability of Bi_(26)Mo_(10)O_(69) porous layer modified ionic-electronic mixed conductor on air side

Bi26MO10O69 nanopowder was prepared by hydrothermal method and used as a surface modification material for oxygen separation membrane to enhance oxygen permeability. Thermal decomposition behavior and phase variation of the precursor were investigated by thermal analyzer （TG-DSC） and high-temperature X-ray diffraction （HT-XRD）. Bi26MO10O69 porous layer was coated on the air side of BaCo0.7Fe0.2Nb0.1O3-δ （BCFN） oxygen permeable membrane by dipping method. In the partial oxidation experiment of coke oven gas （COG）, the Bi26Mo10O69-coated BCFN membrane exhibits higher oxygen permeability and CH4 conversion than the uncoated BCFN membrane. When the thickness of BCFN membrane was 1 mm and the COG and air fluxes were 120 and 100 mL/min, the oxygen permeation flux reached 16.48 mL/（min.cm^2） at 875℃, which was 16.96% higher than the uncoated BCFN membrane. Therefore, Bi26MoloO69 porous layer on the air side will be promising modification coating on the oxygen permeability of BCFN membrane.

Effects of pore size and porosity of surface-modified porous titanium implants on bone tissue ingrowth

The effects of surface-modified porous titanium implants with different porosities and pore sizes on osseointegration were investigated in vivo.Three porous titanium implants(A30,A40 and A50 containing volume fractions of space-holder NaCl being 30%,40%and 50%,respectively)were manufactured by metal injection moulding(MIM).The surface-modified implants were implanted into muscles and femurs of hybrid male dogs.Interface osteogenic activity and histological bone ingrowth of porous titanium implants were evaluated at 28,56 and 84 d.The results showed that when additive space-holder amount of NaCl increased from 30%to 50%(volume fraction),the general porosity and mass fraction of macropores of porous titanium rose from 42.4%to 62.0%and from 8.3%to 69.3%,respectively.Histologic sections and fluorescent labeling showed that the A50 implant demonstrated a significantly higher osteogenic capacity at 28 d than other implants.Bone ingrowth into the A30 implant was lower than that into other implants at 84 d.Therefore,the pore structure of A50 implant was suitable for new bone tissue to grow into porous implant.

Influence of porogen type and copper powder morphology on property of sintering copper porous materials

Copper porous materials have been manufactured by the method of powder metallurgy.Electrolytic copper powders and atomized copper powders are used as matrix material.Methylcellulose and paraffin are used as porogen.The influence of porogen type and copper powder morphology on the property of copper porous materials is investigated as well.The results show that copper porous materials with paraffin as porogen have lower porosity and permeability compared with materials using methylcellulose as porogen,due to the different pore-forming mechanisms.The pore forming mechanism of methylcellulose is thermal decomposition,while the pore forming mechanism of paraffin is melting–evaporation.The morphology of copper powders affects the contact state between adjacent powders,which further influence the sintering shrinkage.The porous materials using arborescent copper powders as matrix have lower porosity,smaller pore size and lower permeability,compared with materials with atomized copper powders as matrix.

Fabrication of lotus-type porous Mg−Mn alloys by metal/gas eutectic unidirectional solidification

Lotus-type porous Mg–xMn(x=0,1,2 and 3 wt.%)alloys were fabricated by metal/gas eutectic unidirectional solidification(the Gasar process).The effects of Mn addition and the fabrication process on the porosity,pore diameter and microstructure of the porous Mg-Mn alloy were investigated.Mn addition improved the Mn precipitates and increased the porosity and pore diameter.With increasing hydrogen pressure from 0.1 to 0.6 MPa,the overall porosity of the Mg-2wt.%Mn ingot decreased from 55.3%to 38.4%,and the average pore diameter also decreased from 2465 to 312μm.Based on a theoretical model of the change in the porosity with the hydrogen pressure,the calculated results were in good agreement with the experimental results.It is shown that this technique is a promising method to fabricate Gasar Mg–Mn alloys with uniform and controllable pore structure.

Air Filter Simulation by Geodict

In this paper, we discussed the relationship of filter effictency and pressure drop with the porosity, fiber diameter and filter thickness by Oeodict. We found that filter efficiency will increase when filter porosity and fiber diameter decreasing or filter thickness increasing. And the pressure drop has a linear relationship with filter thickness and non-linear relationship with filter porosity and fiber diameter. We also compared the simulation results with the real test results by TSI 3160. Although there are some differences, I think Ocodict can be used to predict filter effictency and pressure drop.

Photoconductivity Characteristics of Porous Si

Al was evaporated on the surface of PS which was prepared by electrochemical anodization in HF solution to form a metal/PS/Si/Al junction.The photoconductivity spectrum and other features were measured which present that PS has a stronger visible photoconductivity effect,specially in orange-yellow region.An analysis and discussion were made on it accordingly.

Fabrication and anodic polarization behavior of lead-based porous anodes in zinc electrowinning

A new type of lead-based porous anode in zinc electrowinning was prepared by negative pressure infiltration. The anodic polarization potential and corrosion rate were studied and compared with those of traditional fiat anodes （Pb-0.8%Ag） used in industry. The anode corrosion rate was determined by anode actual current density and microstructure. The results show that the anodic oxygen evolution potential decreases first and then increases with the decrease of pore diameter. The anodic potential decreases to the lowest value of 1.729 V at the pore diameter of 1.25-1.60 mm. The porous anode can decrease its actual current density and thus decrease the anodic corrosion rate. When the pore diameter is 1.60-2.00 mm, the anodic relative corrosion rate reaches the lowest value of 52.1%.

Analysis of mine's air leakage based on pressure gradient matrix between nodes

Air leakage may significantly affect the effectiveness of mine ventilation by in- creasing the cost of ventilation and arousing problems for ventilation management.Fur- thermore,air leakage may accelerate the process of coal spontaneous combustion and cause gas explosion,thus greatly threatens the safety of coal production.The estimation of air leakage,therefore,have great practical significance.For any ventilation system of coal mines,there is a defined pattern of pressure gradient which drived the mine air to flow in the network,drives possible air leakage to go shortcut as well.Air leakage may occur through ventilation structures such as ventilation doors and fractures of the surroun- dig coal and rock of airways.A concept and the relevent calculation method of the pres- sure gradient matrix was put forward to assist the analysis of potential air leakage routes. A simplified example was used to introduce the application principle of'pressure gradient matrix in identifying all the potential air leaking routes,which offers a deeper understand- ing over the ventilation system and the prevention of coal spontaneous combustion.