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51.
基于微观孔隙通道的饱和/非饱和土渗透系数模型及其应用 总被引:2,自引:0,他引:2
从微观角度揭示土体变形对饱和/非饱和渗透系数的影响机理,建立相应的预测方法,对于饱和/非饱和土的渗流分析及水力耦合研究具有重要的科学意义。利用流体力学理论,建立了微观孔隙通道渗透系数与等效孔径的关系,在此基础之上,结合毛细理论建立了饱和/非饱和渗透系数与土-水特征曲线的关系模型,并利用已有试验数据验证了模型的合理性。结合该模型与变形条件下土-水特征曲线预测方法,对变形条件下武汉黏性土饱和/非饱和渗透系数进行预测,结果表明黏性土在压缩变形条件下:饱和渗透系数呈数量级的减小,预测值与实测值均吻合较好;双对数坐标下,非饱和相对渗透系数在进气值之后随基质吸力增加而减小,不同初始孔隙比条件下其斜率近似不变,整体呈现"毛刷型"分布,相同基质吸力条件下,初始孔隙比越小,相对渗透系数越大;非饱和渗透系数,进气值之前近似为饱和渗透系数,进气值之后随基质吸力增大而减小,不同初始孔隙比的变化线近似重合。 相似文献
52.
Permeability characteristics of carbonated concrete considering capillary pore structure 总被引:3,自引:0,他引:3
During carbonation process, the calcium phases present in cement are attacked by CO2 and converted into CaCO3 and the permeability of concrete is changing due to the change in porosity. The rate of carbonation depends upon porosity and moisture content of the concrete. Especially in underground reinforced concrete structures, the interior portion of concrete surface may be exposed to carbonation and the exterior portion of concrete surface exposed to wet soil or underground water. As carbonation proceeds from outer surface into internal portion of concrete, microstructure is also changed continuously from outer surface into internal portion of concrete. Even the deteriorations in the structures due to the carbonation have been reported more, research on permeability characteristics of concrete considering carbonation and micro-structural information is very scarce.In this study, the permeability coefficient in carbonated concrete is derived by applying a capillary pore structure formation model in carbonated cement mortar and assuming that aggregates do not affect carbonation process in early-aged concrete as a function of porosity. The permeability obtained from the micro-level modeling for carbonated concrete is verified with the results of accelerated carbonation test and water penetration test in cement mortar. 相似文献
53.
分子筛催化剂波面移动床传热特性研究 总被引:1,自引:0,他引:1
采用粉粒体传热的两区模型和微元体能量平衡理论 ,研究和分析了不同颗粒粒径的分子筛催化剂对波面移动床换热器各传热系数的影响。实验结果表明 :分子筛催化剂颗粒粒径的大小对壁面传热系数和总传热系数影响大 ,而对中央区的传热系数无影响。 相似文献
54.
通过对双加压法硝酸装置铂网使用情况和铂网脱边事故的统计,分析了氧化炉采用平编三元网存在的问题;论述了经编二元网的特性和优点;计算了铂网的生产强度和接触时间,确定了铂网丝径;总结了硝酸装置使用经编二元网的运行效果和经济效益,结果表明,吨酸氨耗降低了2.48kg,铂耗降低了10mg,经编二元网优于平编三元网。 相似文献
55.
56.
Novel silica nanoboxes were prepared by controlled dealumination of Na-X and Ca-A type zeolites using ammonium hexafluorosilicate (AHFS). The silica-richer
the parent zeolite, the smaller the average pore size produced and the narrower the pore size distribution obtained. This
was due to the specific reactivity of the extracting agent with the zeolite framework aluminum atoms. High temperature calcination
of the dealuminated X-zeolite (ammonium form) resulted in mesoporous materials exhibiting an ink-bottle shape, a quite high
surface area (330 m2/g, no micropores), an average pore diameter of 4.5 nm with a quite narrow pore size distribution (± 1.0 nm) and finally,
a pore opening diameter of 3.9 nm. The latter was determined by using the nitrogen sorption isotherms (BET technique) and
related pore volume data. The sorption behavior also suggested the interconnecting character of the newly created nanoboxes. The periodicity of these nanoboxes throughout the mesoporous material was clearly shown by X-ray powder diffraction at very small angles.
These materials, herein called monomodal nanoboxes because of the absence of micropores in the structure, were also thermally stable. Incorporation of orthosilicate into the obtained silica nanoboxes, in accordance with the recently developed technique for
pore size engineering in zeolites, led to materials with smaller pore openings but having almost the same textural properties. Solid superacidic materials were prepared by incorporating a liquid superacid
(triflic acid or trifluoromethanesulfonic acid) into the silica nanoboxes using the wet impregnation technique. The maximum
triflic acid loading which did not significantly affect the mesoporous framework of the materials was 24 wt%. As a reference,
the maximum loading of less acidic sulfuric acid was slightly lower. All this showed the high chemical stability of the silica nanoboxes for supporting very acidic species. Temperature-programmed desorption using a combined DTA/TGA system
allowed the identification of the bound phases and some liquid phase of the loaded triflic acid. 相似文献
57.
Rock phosphate fractions were examined for their porous structure by nitrogen adsorption. The pore size distribution and the shape of pores does not seem to depend on the particle size. The specific surface area values present two regions, one above and one below that of the particles with 125 μrn diameter. Particles of a given size were leached with dilute phosphoric acid (1.5 mass% P2O5) at 25°C. It was observed that there is a widening of the initial pores during leaching. The particles collected at the initial period of the reaction are pitted and those collected at the final period are disintegrated. 相似文献
58.
59.
The intrinsic rate of diffusion of soluble lignin from fibre walls to bulk liquor has never been determined previously because of experimental difficulties; for example, the diffusion rate determined in a stirred cell is affected by the mechanical action of stirring. In our work, the intrinsic rate of diffusion of lignin macromolecules from the fibre walls of a softwood kraft pulp was determined under alkaline conditions using a displacement cell which eliminated external heat and mass transfer resistances and pulp fibre disturbances. The effects of such experimental conditions as pulp bed height and liquid flow rate were studied. The diffusion rate can be described by a diffusion model for a hollow cylinder with a very wide range of diffusion coefficients. The diffusion rate increased with increasing pH. Our results provide a new understanding of the lignin diffusion process in fibre walls, which is affected by the size of lignin molecules and the pores, and by the electrostatic interactions between intrafibre pore walls and lignin. 相似文献
60.
。以大同精选煤为原料 ,并在制造过程中加入适量化学溶液 ,采用斯列普炉炭化、活化 ,可制得大、中孔发达、吸附性能改善的活性炭。 相似文献